Division of Reproductive Endocrinology, Department of Obstetrics and Gynecology (S.N.K.), University of Ioannina, School of Medicine, 45500 Ioannina, Greece; and Pediatric and Reproductive Endocrinology Branch, National Institute of Child Health and Human Development (G.P.C.), National Institutes of Health, Bethesda, Maryland 20892
Address all correspondence and requests for reprints to: Sophia N. Kalantaridou, M.D., Department of Obstetrics and Gynecology, University Hospital of Ioannina, Panepistimiou Avenue, 45500 Ioannina, Greece. E-mail: kalantas@exchange.nih.gov; and George P. Chrousos, M.D., Chief, Pediatric and Reproductive Endocrinology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Building 10, Room 9D42, Bethesda, Maryland 20892. E-mail: . chrousog{at}mail.nih.gov
Normal puberty is associated with the onset and progressive activation of the hypothalamic-pituitary-gonadal (HPG) axis and the resultant development of secondary sexual characteristics. Puberty begins with increasing nocturnal pulsatile hypothalamic GnRH secretion, which gradually occurs throughout the 24-h day. Pulsatile GnRH stimulates pituitary FSH and LH secretion, ultimately stimulating gonadal steroid production and gametogenesis in females and males. In the ovary, FSH stimulates follicular maturation and estrogen production through aromatization of androgens, whereas LH stimulates androgen production by theca cells, triggers ovulation, and maintains progesterone production by the corpus luteum. In the testis, FSH acts on Sertoli cells to initiate spermatogenesis and LH acts on Leydig cells to stimulate testosterone production.
The hypothalamic-pituitary-adrenal (HPA) axis also has some minor input into the physiological process of puberty, through the secretion of adrenal androgens. However, the major involvement of the HPA axis in puberty is in its potential pathological influence, primarily in accelerating its onset and/or progress.
Traditionally, the onset of adrenal androgen secretion in childhood has been termed "adrenarche," whereas the onset of gonadal steroid secretion has been called "gonadarche." Delayed puberty describes the clinical condition in which the pubertal events start late or are attenuated or arrested. In contrast, precocious puberty describes the clinical condition in which the pubertal events start early.
Mutations have been identified in an increasing number of genes that influence the onset and progression of puberty. These discoveries have provided new insights into the physiology and pathophysiology of this important life transition and have greatly influenced the practice of reproductive medicine. For instance, the concept of two gonadotropins acting on two separate cell types in the gonad has been the cornerstone of reproductive endocrinology, while it has been traditionally believed that both FSH and LH are required for fertility in females and males. However, studies of mutant gonadotropin receptors indicate that female reproductive capacity depends primarily on FSH, whereas male reproductive capacity depends primarily on LH.
We summarize the molecular defects that influence gonadal and/or adrenal function and cause delayed (Table 1) or precocious puberty (Table 2
). Here, we present genes whose alterations result in abnormal puberty in girls and boys.
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Kallmann syndrome is characterized by hypogonadotropic hypogonadism and anosmia/hyposmia, and is transmitted in an X-linked recessive mode of inheritance. Kallmann syndrome is the most common form of isolated gonadotropin deficiency, occurring in 1 in 10,000 males and 1 in 50,000 females (1).
The KAL gene is located in the pseudoautosomal region of chromosome X, at Xp22.3, and encodes a 680-amino acid extracellular matrix protein (2, 3). The KAL protein has homologies to neural cell adhesion molecules, protease inhibitors, neurophysins, phosphatases, and kinases and appears to serve a more generalized role in development (1). A variety of nonsense, missense, and frameshift point mutations or large deletions of the KAL gene have been reported (4). In some cases, Kallmann syndrome includes multiple other anomalies, such as hypoplasia of the cerebellar vermis and other midline structures, and unilateral renal agenesis (5).
The connection between anosmia/hyposmia and hypogonadism can be explained by an embryonic link: immunohistochemistry and in situ hybridization in mouse embryos have demonstrated that both GnRH and olfactory neurons originate in the olfactory placode, with the former migrating into the hypothalamus (6). Furthermore, in a fetus with Kallmann syndrome, lack of GnRH-expressing cells was noted in the brain, despite the presence of dense clusters of GnRH cells and fibers in the nose; in contrast, in normal fetuses, GnRH cells and fibers were observed in the hypothalamus and preoptic area (7).
Approximately half of families with X-linked hypogonadotropic hypogonadism have KAL-1 gene mutations (5), whereas only 5% of sporadic cases have such mutations (8). Interestingly, unilateral renal agenesis occurs in 50% of all males with KAL gene mutations (5). Of note, there is a lack of genotype-phenotype correlation in this syndrome. In a set of two brothers with the same point mutation within KAL, one sibling had hypogonadism, left renal agenesis, and cryptorchidism, while his brother had hypogonadism but none of the associated findings (9).
DAX-1 gene mutations [adrenal hypoplasia congenita (AHC)]
AHC is a rare X-linked disorder characterized by primary adrenal insufficiency and hypogonadotropic hypogonadism (10). The gene responsible for this disorder, DAX-1 (for dosage-sensitive sex reversal, AHC-critical region of the X-chromosome, gene 1), is located on the short arm of the X chromosome (Xp21) encoding a 470-amino acid member of the nuclear hormone receptor superfamily (11). This orphan nuclear hormone receptor has a novel DNA-binding domain that has a unique structure consisting of a 6667 amino acid repeat motif that does not resemble the DNA-binding domain classically found in this region of nuclear receptors. The carboxy-terminal region of DAX-1 has sequence homology with putative ligand domains of several orphan nuclear receptors (12). The DAX-1 gene is expressed in the hypothalamus, pituitary gland, adrenals, and gonads (13).
More than 60 different mutations in DAX-1 have been reported in more than 70 individuals with X-linked AHC (12). Missense mutations in DAX-1 have been identified in the C-terminal ligand-binding domain, whereas frameshift or nonsense mutations have been described in the N-terminal domain (14).The majority of these mutations are frameshift or nonsense mutations resulting in premature truncation of the DAX-1 protein (15).
Boys with DAX-1 mutations present with adrenal failure in infancy or during childhood as a result of a failure of formation of the permanent zone of the adrenal gland (11). At the present time, because of early diagnosis and treatment of adrenal failure, an increasing number of patients with AHC survive. Hypogonadotropic hypogonadism has been recognized as a universal feature of this syndrome in patients who are treated with adrenal steroids and survive beyond childhood. More than 10% of them have bilaterally undescended testes at birth (10, 16), whereas others have normal HPG axis activity in infancy (17, 18). At the time of puberty, they usually present with hypogonadotropic hypogonadism. Nevertheless, spontaneous onset of puberty, but with incomplete pubertal development, has been reported (19). Pulsatile GnRH has been used to induce puberty with poor results, suggesting the functional importance of DAX-1 at the level of the pituitary (16, 20).
Although administration of human chrorionic gonadotropin (hCG) stimulates testosterone concentrations into the normal range in most patients, spermatogenesis using exogenous gonadotropins is difficult to induce, probably reflecting a direct effect of DAX-1 on Sertoli cell function (20). Interestingly, an I439S missense mutation in DAX-1 was recently found in a man who presented with mild adrenal failure and incomplete hypogonadotropic hypogonadism in his twenties (21). Functional studies showed that this mutation caused a partial loss of DAX-1 function in a variety of transient gene expression assays. Thus, partial loss-of-function mutations in DAX-1 can present with hypogonadotropic hypogonadism and covert adrenal failure in adulthood (22).
Female heterozygotes for DAX-1 gene mutations may present with delayed puberty, but normal fertility (21). However, a female homozygous for a DAX-1 nonsense mutation had isolated hypogonadotropic hypogonadism, but apparently normal ovarian development and normal adrenal function (23). In addition, remarkable discrepancy exists in genotype-phenotype relations: the same mutation resulted in two brothers with the complete syndrome, an unaffected grandfather, and an aunt with only hypogonadotropic hypogonadism (23).
NR5A1 [steroidogenic factor-1 (SF-1)] gene mutations
The NR5A1 gene, located at 9p33, encodes for SF-1, an orphan nuclear receptor that plays an essential role in the development of the adrenal gland, testis, ovary, pituitary, and hypothalamus (24, 25). Two cases of NR5A1 gene mutations have been described. The first mutation was reported in a 46,XY individual with female external genitalia who presented with primary adrenal failure during the first weeks of life and persistent müllerian structures (26). The patient had a heterozygous point mutation of the NR5A1 gene in the proximal box of the first zinc finger, an area known to be critical for DNA binding of other nuclear receptors. This mutant SF-1 protein failed to bind to SF-1 response elements and caused no transactivation of a responsive promoter. A moderate gonadotropin response to GnRH was found before the induction of puberty, but with no testosterone response to exogenous hCG, suggesting defective gonadal function. At laparotomy, normal müllerian structures and streak-like gonads containing poorly differentiated seminiferous tubules and connective tissue were found. From this case, it seems that SF-1 is essential for sex determination, steroidogenesis, and reproduction.
The second NR5A1 heterozygous point mutation was recently described in a 27-month-old 46,XX female with normal external genitalia and adrenal failure (27). Although her pubertal development remains to be seen in the future, impaired ovarian development and/or steroidogenesis would be expected.
Prohormone convertase 1 (PC-1) gene mutation
PC-1 converts proinsulin to insulin. A single case of prohormone convertase 1 gene mutation has been reported in a 43-yr-old woman with severe childhood obesity (weight at the age of 3 yr, 36 kg), primary amenorrhea, and defects in converting proinsulin to insulin (28, 29). In addition to the abnormality of proinsulin processing, there was evidence of impaired processing of proopiomelanocortin and secondary mild hypocortisolism, suggesting a more generalized defect related to impaired processing of prohormones (28).
Although the patient developed hypogonadotropic hypogonadism, the development of secondary sexual characteristics was normal. At the age of 30 yr, ovulation was induced with gonadotropins. She became pregnant and delivered healthy quadruplets (28).
Leptin and leptin receptor gene mutations
A male patient was recently reported with a leptin gene missense mutation (30). The patient was homozygous for an Arg105Trp leptin gene mutation and presented with obesity, hyperinsulinemia, no facial hair, sparse pubic and axillary hair, gynecomastia, small penile size, and low testicular volume. Testosterone levels were decreased, but gonadotropins responded normally to GnRH, revealing the hypothalamic nature of the hypogonadism. A leptin receptor mutation produced a similar phenotype in a family with obesity and hypogonadotropic hypogonadism (31).
GnRH receptor gene mutations
GnRH is synthesized in the hypothalamus and carried by the hypothalamo-hypophysial portal system to the gonadotropic cells of the anterior pituitary. Binding of GnRH to receptors on the pituitary gonadotropes causes the release of both FSH and LH.
Patients with GnRH deficiency present with pubertal delay and low serum gonadotropin levels. Although the GnRH gene seems to be the most likely candidate gene for mutations that cause GnRH deficiency in patients with hypogonadotropic hypogonadism, no such mutations have been identified, to date. On the other hand, no confirmed mutations of other hypothalamic-releasing hormones have been described, to date, either, suggesting that the function of hypothalamic hormones is crucial for human physiology and highly conserved (32).
GnRH receptor gene mutations result in hypogonadotropic hypogonadism of autosomal recessive inheritance (33). The GnRH receptor belongs to the G protein-coupled receptor family, which contains an extracellular domain, a seven-transmembrane domain region, three extracellular loops, and three intracellular loops (34, 35). Unlike most G protein-coupled receptors, this receptor does not possess an intracellular carboxy- terminal tail (36, 37). The GnRH receptor gene is located on chromosome 4q13.1 (38). The coding sequence is present in two exons and spans over 20 kb.
Only seven families carrying GnRH receptor defects have been described to date (33, 39, 40, 41, 42, 43, 44). Expression of mutated receptors in heterologous cells showed either GnRH binding defects or decreased phospholipase C activation. In many cases the mutated receptors retained some activity. The first study reported a family in which two siblings, one male and one female, had hypogonadotropic hypogonadism (33). The male patient presented with hypogonadism at age 22 yr. Onset of puberty was noted at 16 yr, but impaired libido was reported. Physical examination revealed absence of facial hair, sparse pubic hair (Tanner stage III), and decreased penile size (6 cm) (33). He had low testosterone concentrations and basal gonadotropin levels. His GnRH-stimulated FSH and LH responses were normal. The patients older sister had a history of primary amenorrhea and infertility, with apparently normal thelarche at 14 yr of age and a single spontaneous menses at 18 yr. Then, she became amenorrheic with low gonadotropins. Ovulation-inducing treatment resulted in two normal pregnancies. Both affected individuals were compound heterozygotes for two different GnRH receptor gene mutations, a missense mutation Gln106Arg in the extracellular domain, and an Arg262Gln mutation in the third intracellular loop.
An interesting feature was observed in another family with GnRH receptor gene mutations: one man and his two sisters were compound heterozygotes for the same mutations (39). The man had a complete form of GnRH receptor deficiency, with absence of pulsatility of endogenous LH and absence of responses to GnRH (single injection or pulsatile administration), whereas the two sisters had no spontaneous pulses of LH but responded to exogenous administration of GnRH (39).
Layman et al. (40) reported another family with GnRH receptor gene mutations, with three affected female members and one affected male. All affected members presented with delayed puberty with low gonadotropin levels and variable response in a GnRH stimulation test. All female patients had primary amenorrhea. The affected individuals were compound heterozygotes for the GnRH receptor gene. The first GnRH receptor gene mutation was an Arg262Gln missense mutation in the third intracellular loop, also described previously (33), and the other mutation was a Tyr284Cys substitution in the sixth transmembrane region (40). When mutant GnRH receptors were transfected into COS-1 cells and cell membrane preparations were used, GnRH binding was minimally affected, although decreased receptor expression was observed and both mutants demonstrated significantly diminished production of inositol 1,4,5-trisphosphate (40).
Recently, a 19 yr-old male patient with delayed puberty was reported to carry a homozygous, completely inactivating mutation of the GnRH receptor (44). He had no facial hair and was bilaterally cryptorchid. Testosterone and basal gonadotropins were low and failed to respond to GnRH . The patient had a point mutation (T for A) at codon 168 of the GnRH receptor gene, resulting in a serine to arginine change in the fourth transmembrane domain. Functional studies with COS-7 cells revealed that this mutation resulted in complete loss of the receptor-mediated signaling response to GnRH (44).
Nevertheless, most of the patients with GnRH receptor gene mutations have incomplete forms of the condition. In one female patient carrying a mutation, pulsatile administration of GnRH induced ovulation and allowed pregnancy (43).
PROP-1 gene mutations [combined pituitary hormone deficiency (CPHD)]
CPHD has an incidence of approximately 1 in 8,000 births (45). Familial occurrences of CPHD are unusual and have been described as transmitted in an autosomal recessive, autosomal dominant, or X-linked recessive manner (46). CPHD can be caused by mutations in transcription factors required for pituitary development, such as POU1F1 (formerly known as Pit1) or PROP-1 (prophet of PIT 1) (47). PROP-1 is located at 5q35. Individuals with mutations of PROP-1 present with short stature, hypothyroidism, and delayed puberty. A variety of PROP-1 mutations have been identified, but the most common mutation is a 301302delAG and accounts for approximately half of familial cases (45). Phenotypic features vary, even between patients with the same mutation (46, 48). The age at diagnosis is dependent on the severity of symptoms, ranging between 9 months and 8 yr of age (47). Initial presentation in all patients is that of growth retardation and failure to thrive due to either GH or TSH deficiency (47). Affected patients may present with spontaneous puberty, but with concentrations of LH and FSH below normal limits, indicating hypogonadotropic hypogonadism (46, 47).
Gonadotropin and gonadotropin receptor gene mutations
Normal pubertal development depends on normal secretory patterns of FSH and LH. These hormones are heterodimers composed of a common -subunit and a specific ß-subunit, each encoded by a separate gene. The
-subunit is common to FSH, LH, TSH, and CG, whereas the ß-subunit is the hormone-specific subunit. Individuals with
-subunit gene mutations have not been reported thus far. Such a person would have hypothyroidism at birth and lack of pubertal development. The LH ß and FSH ß genes are similar in structure, each comprising three exons, and are located on chromosomes 19 and 11, respectively (49, 50).
In the ovary, FSH promotes steroidogenesis through interaction with its receptor on the surface of granulosa cells. The signal promotes the stimulation of the P450AROM enzyme, which results in the aromatization of androstenedione and testosterone to estrogen. FSH also stimulates granulosa cell division and differentiation (51). In addition, LH stimulates theca cell androgen production, triggers ovulation and granulosa cell luteinization, and maintains progesterone production of the corpus luteum.
In the testis, FSH acts on the Sertoli cells and germ cells to facilitate spermatogenesis, whereas LH acts on Leydig cells and promotes testosterone production and male sexual development.
The gonadotropins bind to specific receptors. Both the FSH receptor (FSHR) and the LH receptor (LHR) belong to the G protein-coupled receptor superfamily (51).
FSH ß-subunit gene mutations.
In the female, FSH binding has been localized to the granulosa cells (52), whereas in the male it has been localized to the Sertoli cells (53).
The FSH ß-subunit gene is located at 11p13 (54). Five cases with FSH deficiency caused by mutations in the gene of the ß-subunit of FSH have been described. The first female patient presented with primary amenorrhea and infertility (54). The mutation gave rise to a completely altered amino-acid sequence between codons 61 and 86 of the FSHß chain, which was followed by a premature stop codon, and lack of translation of amino acids 87 to 111. The translated FSHß protein was truncated and unable to couple with the -subunit to form bioactive FSH. The patient had normal adrenarche, but no breast development or menarche (54). She conceived after the induction of ovulation with exogenous FSH. Her mother, a heterozygote for the mutation, had suffered from menstrual irregularity and infertility (54).
The second patient was a teenage girl with delayed puberty, presenting with primary amenorrhea and poorly developed secondary sex characteristics (55). She had undetectable serum FSH and estradiol levels, high LH levels, and an absent FSH response to GnRH. She was a compound heterozygote for two mutations in the FSHß-subunit gene. One mutation was the same as that described previously (54), and the other was a missense mutation that changed a cysteine (TGT) to glycine (GGT) at codon 51 (55). The patients heterozygous relatives were clinically normal (55).
In addition, another woman, initially reported with FSH deficiency due to FSH circulating antibodies (56), was later reevaluated and found to be homozygous for the same 2-bp deletion reported previously (54, 57).
Furthermore, two men with FSHß gene mutations were studied. The first man had normal puberty and virilization but was azoospermic (58). He had small testes and was unsuccessfully treated with recombinant FSH. Analysis of FSHß gene, exon 3, revealed a T to C transition in codon 82 (TGT to CGT) (58). The second man presented with secondary hypogonadism associated with an isolated deficiency of FSH (59). He had a two-nucleotide deletion in the coding sequence for the ß-subunit of FSH, resulting in a truncated polypeptide lacking the last 51 amino acids at the C-terminal end of the subunit (59). The young man had bilaterally descended small, soft testes, high serum LH levels, decreased serum total and free testosterone levels, and azoospermia (59).
FSH receptor gene mutations.
After FSH or LH binding, adenylate cyclase is activated, leading to increases in intracellular cAMP, which activates protein kinase A-mediated protein phosphorylation and results in the cellular effects of the particular gonadotropin. Mutations of the gonadotropin receptors are classified into inactivating (loss-of-function) and activating (constitutively active or gain-of-function) mutations.
The genes for FSHR and LHR are on human chromosome 2p21 (51). The FSHR gene has 10 exons whereas the LHR has 11 exons. The first 9 exons of the FSHR and the first 10 exons of the LHR encode the extracellular domain, whereas the last exon of each gene encodes a small portion of the extracellular domain, seven transmembrane helices, and the C-terminal intracellular domain (60). Binding of hormone to the extracellular domain of either receptor activates the receptor leading to increased formation of cAMP, transcriptional activation of FSH- and LH-responsive genes and steroidogenic changes (60).
Inactivating mutations of the FSHR were initially described in six Finnish families. All affected women presented with primary ovarian failure (61) and were found to be homozygous for a C to T transition at position 566 of exon 7 of the FSHR gene (2p21), indicating an Ala189Val transition. Functional studies using a mouse Sertoli line revealed a nearly complete lack of cAMP production by the mutated receptor on FSH stimulation. The clinical features of these patients included primary or early secondary amenorrhea and anovulation, with variable development of secondary sex characteristics (61, 62). Ovarian biopsy revealed the presence of primordial ovarian follicles (62). The heterozygote mothers of the probands had normal fertility and no menstrual disturbances (61). Additional inactivating mutations of the FSHR resulting in primary amenorrhea have been reported as well (63, 64). Interestingly, in affected individuals, phenotype ranged from absent to variable breast development and primary amenorrhea (Ala189Val mutation) (61, 62) to normal breast development and secondary amenorrhea (compound heterozygous Ile160Thr/Arg573Cys) (63).
These findings indicate that the early stages of follicular maturation are independent of FSH, but the final stages of follicular maturation absolutely require this gonadotropin.
Five male Finnish brothers homozygous for the same inactivating mutation were shown to have normal development of secondary sex characteristics, but variable degrees of spermatogenic failure associated with a great reduction of testicular volume (65). However, none of them was azoospermic and some of them fathered children. Their serum FSH levels were moderately elevated whereas LH serum levels were normal to moderately elevated. These findings indicate that FSH is not essential for male reproduction (65).
An activating mutation of the FSHR gene was reported in a 28-yr-old hypophysectomized man (66). He had been hypophysectomized because of a pituitary tumor and was unexpectedly fertile under testosterone treatment, despite undetectable serum gonadotropin levels (66). Generally, patients with secondary hypogonadism are placed on testosterone replacement to maintain their masculinization. However, these patients usually have a fall in spermatogenesis due to gonadotropin withdrawal, regaining fertility after treatment with FSH and LH. Yet, this patient had normal spermatogenesis and fathered three children (66). Of note, spermatogenesis of this patient was sustained when testosterone replacement therapy was interrupted.
The patient had a heterozygous mutation changing Asp to Gly at position 567, located in the third intracytoplasmatic loop (66). Functional studies performed in transiently transfected COS-7 cells showed that the mutant receptor induced an increased in cAMP production independent of FSH stimulation, suggesting constitutive activity (66). This suggests that FSH alone maintains spermatogenesis in man. The history of hypophysectomy in this patient enabled the identification of the activating FSHR mutation. Nevertheless, the effects of constitutive FSHR activity occurring with normal pituitary function are unknown.
LHß-subunit gene mutations.
The LHß-subunit gene is located at 19q13. A male with a homozygous mutation in exon 3 of the LHß gene (Glu54Arg) presented with delayed puberty and raised immunoreactive LH concentrations but normal FSH measurements (67). A testicular biopsy showed arrested spermatogenesis and absent Leydig cells. Spermatogenesis and testosterone synthesis were stimulated by the administration of hCG (67). This mutation of LHß gene was shown to prevent binding of the LH molecule to the LHR. Three of his uncles who were heterozygous for the mutation were infertile with raised immunoreactive LH concentrations and variably raised FSH concentrations, whereas his mother and sister were fertile (67).
In addition to the mutation described above, other LHß sequence alterations have been reported, which appear to be polymorphisms, producing minimal, if any, negative effect in LH function (32).
LHR gene mutations.
Inactivating LHR mutations result in male pseudohermaphroditism (68, 69, 70, 71, 72, 73, 74, 75, 76), whereas activating LHR mutations lead to familial and sporadic forms of male limited precocious puberty (77, 78), also known as testotoxicosis. LHR activating mutations do not seem to have any particular phenotype in females.
Genetic changes, including single base substitutions, an exon deletion, and an in-frame insertion, have been found to inactivate the LHR (60). Inactivating mutations are recessive in nature.
In affected 46,XY patients, the phenotypes are variable, ranging from phenotypic females (complete male pseudohermaphrodites) to males with micropenis (68, 69, 70, 71, 72, 73, 74, 75, 76). Male pseudohermaphroditism results from the failure of testicular Leydig cell differentiation and /or function (Leydig cell hypoplasia).
Six single base substitutions giving rise to nonsense (Cys545Stop and Arg554Stop) and missense mutations (Cys131Arg, Glu354-Lys, Ala593Pro, and Ser616Tyr) have been identified (68, 69, 70, 71, 72, 73, 74, 75, 76). The majority of these mutations have been found in affected homozygotes, although compound heterozygosity has been identified (68, 69, 70, 71, 72, 73, 74, 75, 76). In vitro expression studies using either HEK293 or COS-7 cells revealed impaired or absent ligand binding and cAMP production in response to hCG stimulation, indicating inactivation or reduced activity of the mutated receptor (68, 69, 70).
Affected 46,XY individuals are born with fully or mildly virilized external genitalia and fail to develop secondary sex characteristics at puberty. These patients usually seek medical attention at puberty because of primary amenorrhea and lack of pubertal changes. They have elevated serum levels of LH, normal levels of FSH, and low levels of testosterone, which do not respond to hCG stimulation. Histological examination of the testes shows absence of Leydig cells (74).
There is a correlation between the severity of the clinical phenotype and the amount of residual activity of the mutated LHR. The severe forms are observed in patients with mutated LHRs that either fail to bind the ligand or are unable to transduce the signal after hormone binding. Milder forms are observed in patients with mutated LHRs that have reduced but not absent hCG binding as signal transduction (69, 75).
Martens et al. (76) reported three brothers with micropenis caused by a homozygous missense mutation resulting in a substitution of a lysine residue for an isoleucine at position 625. They were referred with absence of pubertal signs and infertility due to azoospermia. Spermatogenesis in these patients progressed up to the late stages of spermatid differentiation. In one of the patients, 2 yr of testosterone treatment resulted in a significant increase in sperm count (from azoospermia to 3 x 106 spermatozoa/ml) and fertility (76).
In the female, inactivation of the LHR causes hypergonadotropic hypogonadism and primary amenorrhea. We have described the first occurrence of a woman with homozygous inactivating mutation in the LHR gene (70). This patient was a 46,XX sister of three male pseudohermaphrodites. She was referred for evaluation of amenorrhea at the age of 22 yr. Normal breast and pubic hair development occurred at the expected ages. She had a small uterus and cystic ovaries (70). A homozygous Arg554Stop codon was identified in this patient, as well as in her siblings, resulting in an LHR truncated at the level of the third intracellular loop (70). To date, only four genetic females with inactivating LHR gene mutations have been described (70, 71, 73). All of them were sisters of 46,XY patients with pseudohermaphroditism related to Leydig cell hypoplasia. Four distinct homozygous inactivating mutationsone missense (Arg554Stop), one deletion (Leu608, Val609), and two missense (Glu354Lys and Ala593Pro)of the LHR were identified in these women leading, to a phenotype of ovarian resistance. They have spontaneous breast development, primary or secondary amenorrhea, and infertility. Spontaneous vaginal bleeding occurred at variable intervals, whereas withdrawal bleeding after progesterone administration occurred in all patients. Serum LH and LH/FSH ratio were elevated (70, 71, 79). The presence of normal early follicular estradiol levels in these patients reveals that FSH alone can stimulate sufficient estrogen production for normal pubertal development in females.
Familial male limited precocious puberty (also called testotoxicosis) is inherited as an autosomal dominant disorder and is caused by heterozygous activating mutations of the LHR (60, 77, 78). Sporadic cases may also occur (60).
The disease usually presents by age 14 yr with signs of puberty, rapid virilization, growth acceleration, and adult short stature due to premature epiphyseal closure (77, 78). Affected males show elevated testosterone levels associated with low LH levels and prepubertal responses to the GnRH stimulation test (77). Histological examination of testicular biopsy shows hyperplasia of Leydig cells (77). Maturation of the HPG axis and fertility are usually preserved in boys with male limited pseudoprecocious puberty.
G protein-coupled receptors share a hot spot for activating mutations in the third intracytoplasmic loop and adjacent fifth and sixth transmembrane domains. Expression of these mutations results in raised basal cAMP production compared with wild-type receptors. Activating mutations have been found within exon 11 of the LHR gene (60, 77, 78). The most common mutation is Asp578Gly (60), which occurs in helix VI. The cells transfected with cDNAs for the LHR mutants exhibit markedly increased cAMP production in the absence of agonist, suggesting autonomous Leydig cell activity (60).
Activating mutations of the LHR have no apparent effect on females (80). This is probably due to the fact that it is FSH that determines ovarian growth and maturation. Interestingly, this finding is in contrast to an animal model overexpressing LH, which exhibits infertility, polycystic ovaries, and ovarian tumors (81).
Therapy consists of androgen antagonists to block testosterone effects and aromatase inhibitors to prevent accumulation of estrogen and feminization of the patient during antiandrogen therapy.
Estrogen receptor gene mutation (estrogen resistance)
A single case has been reported of a 28-yr-old man with a homozygous autosomal recessive mutation in the estrogen receptor (82). He had normal onset of puberty. The major phenotypic manifestations of estrogen resistance that he demonstrated were tall stature with evidence of continued slow linear growth, markedly delayed skeletal maturation, and osteoporosis. He was homozygous for a Arg157X (exon 2) mutation in the estrogen receptor
gene (82). Thus, the translated protein was predicted to be truncated, lacking both the DNA-binding and hormone-binding domains (82).
Androgen receptor gene mutations [androgen insensitivity syndrome (AIS)]
The androgen receptor mediates androgen signaling in the cell and is essential for growth, function, and differentiation of the male urogenital tract and external genitalia and secondary male sex characteristics. The X-linked AIS describes a heterogeneous group of defects in the androgen receptor, resulting in varying degrees of defective masculinization in 46,XY individuals (83). The androgen receptor belongs to the steroid superfamily of nuclear hormone receptors. The eight exon gene encodes for a protein containing an amino-terminus, a DNA-binding domain, and carboxy-terminal androgen-binding domain (83).
More than 300 different mutations (commonly missense mutations) in the androgen receptor gene have been reported causing AIS (84). The phenotypic spectrum ranges from a completely female phenotype, with testes but absent wolffian and müllerian duct derivatives and absent sex-dependent hair, to an infertile or undervirilized male phenotype. Approximately 60% of AIS patients have other affected relatives (85).
Amino acid substitution mutations in the ligand- and DNA-binding domains can produce impaired to complete lack of response to androgens. In general, mutations in the ligand-binding domain reduce or abolish androgen binding (86). In complete AIS, the external genitalia are female (male pseudohermaphroditism). These 46,XY phenotypic females have a pubertal growth spurt despite resistance to action of testosterone. The adult height of these patients is greater than normal women, but less than normal men (87).
In partial AIS (PAIS), the external genitalia are ambiguous. At puberty, patients with PAIS usually have gynecomastia, reduced sex hair, and impaired spermatogenesis. In milder forms of the AIS, the external genitalia are male, but affected individuals may have micropenis or hypospadias (85, 88).
Sex assignment at birth of patients with PAIS is based on the virilization of the external genitalia, the testosterone response to hCG, and the potential for raising a "functional" male. Sex assignment of patients with PAIS cannot be based on a specific identified androgen receptor gene mutation, because distinct phenotypic variation in affected families is relatively frequent (85). In addition, a significant parameter to be considered for genotype/phenotype studies is the presence of a possible somatic mosaicism for the androgen receptor gene mutation, which can modulate the phenotype (89, 90).
5-Reductase 2 gene mutations (5
-reductase deficiency)
Subjects with steroid 5-reductase 2 deficiency are 46,XY males who have external female or mildly virilized phenotype at birth and bilateral testes, who virilize at puberty (91, 92, 93). The gene encoding 5
-reductase type 2 is located on chromosome 2 (94, 95, 96, 97). The disease is inherited in an autosomal recessive manner, due mostly to missense mutations of the 5
R2 gene. Some mutations inactivate the enzyme, whereas other mutations impair enzyme function by affecting substrate or cofactor binding (94, 95). Affected 46,XY individuals are born with female external genitalia and raised as girls until puberty, when masculinization occurs. Reports of spermatogenesis range from greatly impaired (97, 98) to normal (99).
Females homozygous for 5-reductase deficiency are apparently normal and have regular menses (97).
P450arom gene abnormalities
CYP19 gene mutations (aromatase deficiency).
Aromatase (P450arom), the last enzyme in estrogen biosynthesis, catalyzes the conversion of androgens to estrogens, and belongs to the cytochrome P-450 superfamily. It is composed of aromatase cytochrome P450 (P450arom) and flavoprotein NADPH-P450 reductase (100). P450arom is encoded by the CYP19 gene localized on chromosome 15p21.1 (101). Aromatase deficiency is inherited in an autosomal recessive manner. The syndrome is more prominent in nonsense mutations of the CYP19 gene.
During pregnancy, because of the aromatase deficiency, large androgen amounts are transferred to the maternal and fetal circulation, resulting in virilization of the mother, and masculinization of the external genitalia in female embryos.
There are reports of two adult males and six girls with aromatase deficiency (101, 102, 103, 104, 105, 106, 107). In the male patients, the first clinical signs were apparent in adulthood. They had macro-orchiditism, with normal sexual activity. They were tall, with a history of a continued linear growth with unfused epiphyses in their twenties associated with osteopenia (101, 102, 103).
Females with aromatase deficiency have pseudohermaphroditism and show progressive virilization at puberty with increased levels of plasma androgens (104, 105, 106, 107). They present with primary amenorrhea, polycystic ovaries, and no female secondary sex characteristics, associated with hypergonadotropic hypogonadism, tall stature, delayed skeletal maturation, and osteopenia. Therapy is rational (i.e. replacement of estrogen and progesterone).
Aromatase excess syndrome.
We recently reported a kindred with aromatase excess syndrome inherited in an autosomal dominant manner, in which affected males had heterosexual precocious puberty and/or gynecomastia, and affected females had isosexual precocious puberty and/or macromastia (108). Symptoms were manifested around the time of adrenarche with greatly advanced bone age and accelerated growth. A 9-yr-old boy presented with gynecomastia. His 7.5 yr-old sister had precocious puberty, with breast development and pubic hair at Tanner stage III with absence of clitoromegaly. Their father and paternal grandmother had peripubertal gynecomastia and macromastia, respectively (108). The father had undergone bilateral mastectomy at the age of 15. The hCG and ACTH stimulation tests and a 3-yr follow-up evaluation of family members suggested that most of the aromatization took place in extragonadal tissues, which included the breast and probably the adrenal glands (108). The source appeared to be nongonadal conversion of adrenal androgens to estrogens. Markedly increased aromatase activity was found in fibroblasts and Epstein-Barr virus-transformed lymphocytes from the patients (108). A new 5'-splice variant was present in the P450arom mRNA, revealing another first exon of this gene, which appeared to be aberrantly expressed in this family. Because of the predicted short final height, both young patients were treated with an aromatase inhibitor and a GnRH analog, which successfully delayed skeletal and pubertal development (108).
17ß-Hydroxysteroid dehydrogenase (HSD) 3 gene mutations (HSD17B3 deficiency)
Autosomal recessive mutations in HSD17B3 gene impair the formation of testosterone in the fetal testis and give rise to 46,XY individuals with female external genitalia (male pseudohermaphroditism) (109). This disorder is the result of a defect in the final step in testosterone synthesis in the testes (i.e. conversion of androstenedione to testosterone). 46,XY homozygotes or compound heterozygotes for mutations in HSD17B3 gene have testes located in the inguinal canals or labia majora and normally developed wollfian duct derivatives. Such individuals are usually raised as females, but virilize during puberty, probably due to extratesticular conversion of androstenedione to testosterone (109). 46,XX HSD17B3-deficient individuals are normal asymptomatic females (110).
Genes defective in congenital adrenal hyperplasia (CAH)
CAH describes a group of inherited autosomal recessive disorders characterized by an enzymatic defect in cortisol biosynthesis, with compensatory increases in corticotropin secretion and hypertrophy and hyperplasia of the adrenal cortices (for a review see Ref. 111). CAH may result from a deficiency in any of the five enzymes necessary to synthesize cortisol from cholesterol [i.e. cholesterol desmolase (P450scc), 3ß-HSD, 17-hydroxylase (P450c17), 21
-hydroxylase (P450c21), and 11ß-hydroxylase (P450c11)] (112). Cholesterol (or 20,22) desmolase, 17-hydroxylase, and 17,20- desmolase are associated with deficient gonadal androgen and estrogen secretion and cause delayed puberty in both sexes. 21-Hydroxylase, 11-hydroxylase, and 3ß-HSD deficiencies are associated with androgen excess and cause varying degrees of virilization and, hence, precocious puberty in both sexes.
CYP 21 gene mutations.
21-Hydroxylase deficiency is responsible for more than 95% of CAH cases and is one of the most common known autosomal recessive disorders (111). The gene for 21-hydroxylase deficiency, CYP21B, lies on chromosome 6 within the human leukocyte antigen locus of the major histocompatibility system (113). Two homologous genes result from ancestral duplication. CYP21B is the active gene, and CYP21A is an inactive pseudogene. CAH is caused by large mutations (deletions or conversions) or point mutations in the CYP21B. These mutations cause different degrees of impairment of enzyme activity, which are responsible for the wide spectrum of clinical manifestations of the disease. Most patients are compound heterozygotes and the severity of the disease is determined by the activity of the less severely affected allele.
Males with classic CAH due to 21-hydroxylase deficiency present with isosexual precocious puberty, whereas females present with heterosexual precocious puberty. Accelerated skeletal maturation and resultant adult short stature occur in both sexes. The age at diagnosis in males varies according to the severity of mineralocorticoid deficiency or salt loss. Males with salt loss typically present at 714 d of life with vomiting, weight loss, hyponatremia, and hyperkalemia whereas males without salt loss present with precocious puberty, characterized by pubic hair and accelerated growth at 25 yr of age (111).
Females with classic CAH typically present at birth with ambiguous genitalia because of exposure to high levels of androgens in utero. Occasionally, genital ambiguity can be profound enough to cause incorrect sex assignment at birth (111).
The nonclassic form of 21-hydroxylase deficiency is mild and is usually recognized peripubertally (111). Although the same gene is involved in both the severe and mild forms, at least one of the genetic mutations associated with nonclassic CAH only mildly impair 21-hydroxylase activity. Males may present with slightly advanced puberty and bone age. In addition, growth of adrenal rest tissue in the testes may lead to oligospermia or azoospermia and infertility. Females present with hyperandrogenism, and the clinical spectrum includes early adrenarche, menstrual irregularities, polycystic ovaries, cystic acne, hirsutism, and/or male pattern baldness.
CYP11B1 (11ß-hydroxylase) and 3ß-HSD/ 5-
4-isomerase (3ßHSD2) gene mutations.
11ß-Hydroxylase deficiency and 3ßHSD are responsible for less than 5% of cases with CAH. 11ß-Hydroxylase deficiency results from mutations in the CYP11B1 gene and presents with hyperandrogenism with or without hypertension and hypokalemic alkalosis (114).
3ßHSD deficiency results from mutations in the HSD3B2 gene. Whereas in 21- and 11ß-hydroxylase deficiencies the defect is restricted to adrenal function, in 3ß HSD2 deficiency it impairs both the adrenals and the gonads. In newborns, 3ßHSD deficiency presents with incomplete masculinization of genetic males or male pseudohermaphroditism, whereas genetic females have normal external genitalia or mild ambiguity. During childhood, signs of androgen excess develop in both sexes (114).
CYP11A (P450scc) gene mutations [cholesterol (or 20,22) desmolase deficiency].
Cholesterol 20,22 desmolase (P450scc) is the mitochondrial cholesterol side chain cleavage enzyme catalyzing the conversion of cholesterol to pregnenolone. The P450scc gene, CYP11A, is located on chromosome 15 (112). CYP11A gene mutations initially were thought to cause congenital lipoid adrenal hyperplasia; however, these patients were shown to lack P450scc mutations (115).
It is believed that P450scc mutations (20,22 desmolase deficiency) are incompatible with human term gestation, because P450scc is required for placental biosynthesis of progesterone, which is necessary to maintain pregnancy (116). Thus, a human fetus homozygous for a P450scc mutation will spontaneously abort at approximately 6 wk of gestation, when production of progesterone from the maternal corpus luteum wanes (116). A heterozygous P450scc mutation was recently described in a 46,XY patient with male pseudohermaphroditism and adrenal insufficiency (117). This patient goes against the dogma that all CAHs are autosomal recessive.
Steroidogenic acute regulatory protein (StAR) gene mutations.
Congenital lipoid adrenal hyperplasia (lipoid CAH) is a rare autosomal disorder, characterized by impaired synthesis of all the adrenal steroids, including mineralocorticoids, glucocorticoids, and sex steroids (118). It is the most severe genetic disorder of steroid hormone biosynthesis, caused by mutations in the gene for StAR. StAR functions as a labile protein factor in steroidogenesis assisting with cholesterol transport within mitochondria (119, 120, 121).
Patients with lipoid CAH have a severe defect in adrenal and gonadal steroidogenesis. Deficient adrenal steroidogenesis leads to neonatal salt wasting, hyponatremia, hyperkalemia, and dehydration (122). Both 46,XY and 46,XX affected individuals have phenotypically normal female genitalia (118). However, 46,XX individuals may undergo spontaneous puberty with cyclical menstrual bleeding (123).
StAR missense, nonsense, and frameshift gene mutations have been identified causing lipoid CAH (124, 125). All missense mutations are found in exons 57, whereas nonsense and frameshift mutations are found throughout the gene (124, 125).
CYP17 gene mutations (17-hydroxylase/17,20 lyase deficiency).
CAH due to 17-hydroxylase/17,20 lyase deficiency is an autosomal recessive disorder caused by mutations on the CYP17 gene, located on chromosome 10q24-q25, that encodes P45017
(112). P45017 catalyzes both 17
-hydroxylase and 17,20-lyase reactions in adrenal glands and gonads. In adrenals, the compensatory ACTH hypersecretion stimulates the synthesis of a large quantity of 11-deoxycorticosterone and corticosterone, which leads to hypertension with or without hypokalemic alkalosis. In gonads, deficiency of 17,20 lyase activity prohibits androgen synthesis leading to a female phenotype and sexual infantilism in both sexes (126, 127). Many mutations of this gene have been described (128, 129, 130). Affected 46,XX females may undergo ovulation induction for in vitro fertilization (131, 132), but the endometrial response to steroid hormone replacement is poor (132).
Glucocorticoid receptor gene mutations (glucocorticoid resistance)
Inactivating mutations of the glucocorticoid receptor gene are causing compensatory elevations of corticotropin and cortisol with associated elevations of adrenal androgens and steroids with mineralocorticoid actions (for a review see Ref. 133). Adrenal androgen excess may rarely lead to precocious puberty. The glucocorticoid receptor gene consists of 10 exons. In our first family with glucocorticoid resistance, a point mutation led to a nonconservative amino acid subsitution from aspartate to valine at position 641 at the ligand-binding domain of the receptor. In a functional assay using COS-7 cells, the nucleotide substitution resulted in a low-affinity, poorly transactivating glucocorticoid receptor. In the glucocorticoid resistant members of our second family, we found a heterozygous 4-bp deletion identified at the 3'-boundary of exon 6 and intron 6. This deletion removed a donor splice site in one of the two glucocorticoid receptor gene alleles leading to expression of only the undeleted allele. Several other glucocorticoid receptor defects have been reported, subsequently, two of them amino acid substitutions, respectively, altering the nuclear translocation of the receptor or its binding to p160 nuclear receptor coactivators (134, 135). Both types of mutant receptors exerted dominant negative activity on the wild-type receptor.
The treatment of this condition is replacement with high doses of synthetic glucocorticoids, such as dexamethasone, with no intrinsic salt-retaining activity (133).
G-protein s gene mutations (McCune-Albright syndrome)
The McCune-Albright syndrome is a heterogeneous clinical condition characterized by a clinical triad: isosexual precocious puberty, bone fibrous dysplasia, and cutaneous café-au-lait spots (136). In addition, hyperthyroidism, hypercortisolism, GH, and prolactin hypersecretion have been described (137). McCune-Albright syndrome is caused by a postzygotic missense activating mutation at arginine-201 of the gene coding for the -subunit of the Gs protein, which is coupled with and tranduces the effect of many protein hormones (138).
McCune Albright syndrome usually occurs sporadically and is more common in girls than in boys (136). Precocious puberty is diagnosed in prepubertal girls, because of breast and pubic hair development, menarche, and estrogenization of external genitalia. Often, ovarian cysts are observed as a sign of ovarian follicle hyperactivation. Precocious puberty is diagnosed in prepubertal boys, because of testicular volume greater than 4 ml, masculinization of genitalia, and pubic hair development. In all cases, autonomous gonadal hyperactivity is demonstrated by the rise of gonadal sex steroids with concomitant suppression of gonadotropin secretion, both basal and following GnRH stimulation.
The rational treatment of this condition consists of a combination of aromatase inhibitors and androgen antagonists.
Conclusions
The functions of the HPG and HPA axes are intricately intertwined, and genetic defects in either axis may affect pubertal development. Specific gene mutations, causing delayed or precocious puberty, have recently been described. The discovery of these naturally occurring mutations have unraveled the roles and pathological significance of these genes in the process of puberty.
KAL1, the first gene defect to be elucidated in X-linked Kallmann syndrome, is a neural cell adhesion molecule, anosmin. Anosmin is required for normal migration of olfactory and GnRH neurons from the olfactory placode to the hypothalamus (2, 3). It seems that there are other genetic causes of Kallmann syndrome, including autosomal recessive forms (4), but the responsible genes have not been identified as yet.
Mutations in two developmental transcription factors (DAX-1 and SF-1) can also result in hypogonadism (12). DAX-1 encodes a transcription factor that plays a key role in the development and function of the hypothalamus, pituitary, gonads, and adrenal cortex (12). DAX-1 defects result in X-linked hypogonadotropic hypogonadism associated with AHC. SF-1 is an orphan nuclear receptor that plays a key role in the development and function of the HPG axis and the adrenal gland. An individual with a heterozygous mutation of SF-1 has been reported with XY sex-reversal, persistent müllerian structures, and primary adrenal failure (24). In contrast to the hypogonadotropic hypogonadism of DAX-1 defects, this patient had hypergonadotropic hypogonadism, suggesting that DAX-1 is more important than SF-1 at the hypothalamic and pituitary level.
A defect in PC-1 has been shown to disrupt GnRH, insulin and proopiomelanocortin processing, leading to hypogonadotropic hypogonadism and obesity (28, 29). Of note, the interplay between reproduction and metabolic homeostasis is also shown by the fact that defects in leptin or its receptor result in hypogonadotropic hypogonadism and obesity (30, 31).
Mutations of the GnRH gene have been sought in humans with GnRH deficiency, but have not been identified thus far. Defects in the gene encoding the GnRH receptor, on the other hand, have been identified and result in isolated hypogonadotropic hypogonadism, with the phenotype varying with the extent to which GnRH binding and signaling is affected (33, 40, 44). Mutations in PROP-1, a pituitary transcription factor involved in the differentiation of several pituitary cell lineages, result in combined pituitary hormone deficiency, short stature, hypothyroidism, and hypogonadotropic hypogonadism (46, 47).
Inherited disorders of the pituitary gonadotropins and their receptors are rare. No mutations of the common -subunit gene have been reported. In the female, the phenotype associated with FSHß-subunit gene mutations and inactivating FSHR gene mutations is associated with primary amenorrhea and poorly developed secondary sex characteristics (54, 55, 56, 57, 61). Affected 46,XX individuals possess primordial follicles and may also have antral follicles. These findings reveal that FSH is important for estrogen production, normal pubertal development, and fertility. On the other hand, FSH is not essential for follicular development up to small antral follicle stage but seems to be required for further follicular maturation. FSHß gene mutations produce a similar phenotype as for FSHR gene mutations, except that the former result in hypogonadotropic hypogonadism, whereas the latter result in hypergonadotropic hypogonadism. In the male, FSHß gene mutations have been associated with azoospermia (58, 59).
Of note, the role of FSH has been shown in the male by the identification of a hypophysectomized patient with an activating mutation of the FSHR (66). This patient, under testosterone substitution, was unexpectedly fertile despite undetectable serum gonadotropin levels. This finding suggests that FSH has a positive role in the maintenance of spermatogenesis in man. Nevertheless, the effects of the lack of FSH action are unclear; although men with a homozygous inactivating mutation of the FSHR have a reduction of testicular volume and sperm output, none of them had azoospermia (65).
Defects in LH-LHR interaction have a strong impact on the male phenotype. Inactivating mutations in the ß-subunit of LH leads to a histological absence of Leydig cells, lack of spontaneous puberty, and azoospermia (67). Activating mutations of the LHR result in male limited precocious puberty (60), whereas inactivating mutations lead to male pseudohermaphroditism (68, 69, 70, 71, 72, 73, 74, 75, 76). The discrepancy between the phenotypes of LH ß and LHR mutations implies that the LHR may have an important role in the stimulation of fetal testicular testosterone production and male sexual differentiation in utero.
Females with LH resistance due to inactivating mutations of the LHR gene have spontaneous breast development, mildly hypoestrogenized uterus, and primary or secondary amenorrhea (70). The presence of normal early follicular estradiol levels in these patients reveals that FSH alone can stimulate sufficient estrogen production for almost complete pubertal feminization.
The identification of males with estrogen deprivation, such as estrogen resistance (82) and aromatase deficiency (101, 102, 103), have challenged long-held concepts regarding the role and effects of estrogen in the male. It is now clear that estrogen has a critical role in male skeletal development and health. Estrogen resistance and aromatase deficiency are characterized by tall stature with linear growth continuing into adulthood, delayed bone age, lack of epiphyseal fusion, and marked osteoporosis. Interestingly, pregnant mothers of fetuses with the aromatase deficiency syndrome are frequently mildly androgenized during pregnancy because of the inability of the placenta to aromatize fetal adrenal androgens to estrogens.
Androgens mediate the development of the normal male phenotype through the androgen receptor. Abnormalities altering the function of androgen receptor result in a variety of phenotypic abnormalities, ranging from complete testicular feminization (female phenotype) to minor degrees of undermasculinization (83).
In the aromatase excess syndrome, affected males present with heterosexual precocious puberty and/or gynecomastia and affected females present with isosexual precocious puberty and/or adult macromastia (108). Aromatase inhibitors have been used along with androgen antagonists to decrease aromatization of androgens and prevent androgen built-up actions via the androgen receptor.
CAHs are associated with hypertrophy and hyperplasia of the adrenal cortices (111). Apparently, the absence of normal cortisol production during adrenal organogenesis results in dysplasia and hypofunction of the adrenal medulla (i.e. epinephrine deficiency) (111). The clinical significance of the latter is unclear but removes the argument against adrenalectomy in very severe cases of CAH. Cholesterol (or 20,22) desmolase, 17-hydroxylase, and 17,20-desmolase abnormalities are associated with deficient gonadal androgen and estrogen secretion and cause delayed puberty in both sexes. Of these, the first is extremely rare and has been associated once with a heterozygous defect of the enzyme (117). Individuals with StAR gene mutations have a severe defect in adrenal and gonadal steroidogenesis, and both 46,XY and 46,XX individuals are phenotypically females (119, 120, 121, 122). 21-Hydroxylase, 11- hydroxylase, and 3ß-HSD deficiencies are associated with androgen excess and cause varying degrees of virilization and, hence, precocious puberty in both sexes.
The molecular defect in the McCune-Albright syndrome, a postzygotic activating mutation of the gene coding for the -subunit of the Gs protein, explains the clinical manifestations of the syndrome as activation in the function of cells in the ovary, the bone, and the skin: isosexual precocious puberty, bone fibrous dysplasia, and cutaneous café-au-lait spots (136). This condition responds to treatment with aromatase inhibitors plus androgen antagonist, while the ovaries produce estrogen autonomously, and with GnRH analogs once central puberty has started.
The molecular insights gained into pubertal physiology and pathophysiology have already led to rational therapies for some of these conditions, including familial male sexual precocity, McCune-Albright syndrome, aromatase excess syndrome, and glucocorticoid resistance, as discussed here.
Acknowledgments
Footnotes
Abbreviations: AHC, Adrenal hypoplasia congenita; AIS, androgen insensitivity syndrome; CAH, congenital adrenal hyperplasia; CPHD, combined pituitary hormone deficiency; FSHR, FSH receptor; hCG, human chrorionic gonadotropin; HPA, hypothalamic-pituitary-adrenal; HPG, hypothalamic-pituitary-gonadal; HSD, hydroxysteroid dehydrogenase; LHR, LH receptor; PAIS, partial AIS; PC-1, prohormone convertase 1; SF-1, steroidogenic factor-1; StAR, steroidogenic acute regulatory protein.
Received March 26, 2002.
Accepted April 10, 2002.
References