Department of Gynecology and Obstetrics, School of Medicine and Biomedical Sciences and Children's Hospital, The State University of New York at Buffalo, 219 Bryant Street, Buffalo, New York, USA 14222. E-mail: Ucheezeh{at}aol.com
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Abstract |
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Key words: azoospermia/clinical classification/male infertility/obstructive and non-obstructive/pre and post-testicular
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Introduction |
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Why is azoospermia classified as obstructive or non-obstructive?
Although azoospermia can be due to genital tract obstruction, defective spermatogenesis, ejaculatory duct dysfunction or hypogonadotrophism, it is currently classified as obstructive and non-obstructive. This is because hypogonadotrophic azoospermia and ejaculatory duct dysfunction are rare causes of azoospermia, accounting for about 2% of azoospermia (Hull et al., 1985). Defective spermatogenesis in 60% and genital tract obstruction in 40% of 102 patients with azoospermia evaluated with testicular biopsy and distal vasography were reported (Matsumiya et al., 1994
). None of the patients in this series had ejaculatory dysfunction or hypogonadotrophic hypogonadism. Out of the 96 consecutive patients with azoospermia evaluated at Sheffield, 58% had defective spermatogenesis, 31% genital tract obstruction, 7% had features likely to be associated with retrograde ejaculation and 3% were of endocrine origin (unpublished data).
Most of the endocrine causes of azoospermia have usually been addressed by the medical endocrinologists by the time the patients are ready to have children. The frequency of hypogonadotrophic azoospermia in an infertility clinic is less than 0.5%. The acquired forms of hypogonadotrophic hypogonadism seen in an infertility clinic include radiation therapy and some brain tumours, such as craniopharyngioma and prolactinoma. The main congenital type is Kallmann's syndrome, which occurs in 1 in 10 000 males at birth. In addition, men with hypogonadotrophic azoospermia, like those with defective spermatogenesis, are usually present with testicular atrophy. However, plasma follicle-stimulating hormone (FSH) concentration is usually low or normal in those with hypogonadotrophic azoospermia.
Azoospermia is also an uncommon presentation of ejaculatory duct dysfunction. These patients usually present with low volume ejaculate with oligospermia or aspermia rather than azoospermia. Ejaculatory duct dysfunction may be due to either failure of emission or retrograde ejaculation. Those with failure of emission usually present with aspermia while those with retrograde ejaculation present with low ejaculate volume and oligozoospermia (Jarow, 1998). However, the secretions of the bulbo-urethral gland, which normally comprise a small part of normal semen, may be ejaculated in an antegrade manner separate from the rest of the ejaculate so that the patient may notice small semen which shows azoospermia (Pryor, 1994
). Nevertheless, it appears that the prevalence of ejaculatory dysfunction may vary from one clinic to the other. Retrograde ejaculation in 18% of men with azoospermia was reported (Yvette et al., 1994). However, there is a general consensus that defective spermatogenesis and genital tract obstruction are the main causes of azoospermia seen in an infertility clinic.
Are clinical protocols appropriate for the classification of azoospermia?
A number of clinical protocols are already in place for the selection of men with various forms of azoospermia. An example of such a protocol is shown in Table I (Ezeh et al., 1999
), which is similar to that proposed by Sharif (2000). One important difference between the two protocols is Sharif's failure to classify those with idiopathic azoospermia. Men with idiopathic azoospermia constitute an important group of men with azoospermia. Previous reports had demonstrated that this group may constitute up to 4850% of men with non-obstructive azoospermia (WHO, 1989
; Jecquier and Holmes, 1993). However, recent studies suggest that many of the so-called idiopathic azoospermia may have a genetic basis. That is why idiopathic azoospermia has been classified under defective spermatogenesis (testicular disorder) in Table I
.
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Testicular histology combined with or without surgical exploration of the genital tract is the gold standard for the distinction of defective spermatogenesis from genital tract obstruction as a cause of azoospermia. Those with normal spermatogenesis are presumed to have obstructive azoospermia while hypospermatogenesis, maturation arrest, Sertoli cell only and tubular sclerosis indicate azoospermia due to defective spermatogenesis. However, testicular biopsy has its own limitations in clinical settings. First, the information from testicular histology is not always available at the time of the patients' initial consultation, making patient selection with such information difficult. Second, testicular biopsy with or without genital tract exploration is invasive, even when performed with percutaneous needle biopsy. For these reasons, patient selection for a specific type of sperm retrieval technique is usually based on a set of clinical parameters, especially the plasma FSH concentration and testicular volume: normal FSH concentration and testicular volume indicate obstructive azoospermia while testicular atrophy and raised FSH indicate defective spermatogenesis. However, these two parameters are usually normal in up to 57% men with maturation arrest histological pattern (Ezeh et al., 1998). The selection of patients on the basis of raised plasma FSH concentration and testicular atrophy alone therefore wrongly excludes many patients with maturation arrest. This observation gave rise to the use of more detailed clinical protocols in deciding which patient should receive which type of sperm retrieval technique or treatment (Ezeh et al., 1999
).
A more fundamental question to ask is whether the clinical protocols (Ezeh et al., 1999; Sharif, 2000
) provide a better approach to the classification of azoospermia than the current method (obstructive and non-obstructive)? At the moment, there is no prospective study comparing the efficacy of the clinical protocols proposed by Sharif (2000) and Ezeh et al. (1999) and the current classification in reaching the diagnosis of the various types of azoospermia. It is the therefore difficult to chose one classification in favour of the other. There is another limitation of the clinical protocol. Although azoospermia with normal plasma FSH concentration and testicular volume suggests genital tract obstruction, raised plasma FSH concentration does not always exclude genital tract obstruction or vice versa. For example, Hauser et al. (1995) described 21 post-vasectomy patients with significant elevation of plasma FSH concentration, and yet they showed normal spermatogenesis on testicular biopsy and the presence of obstructive lesions in the vas or epididymis on surgical exploration. On the other hand, Hendry et al. (1990) reported the presence of defective spermatogenesis in 35 out of 370 (9.5%) patients with normal FSH thought to have obstructive azoospermia. As Sharif pointed out, difficulties may arise in classifying a man who at one time had a vasectomy but later developed testicular dysfunction due to chemotherapy. Neither his protocol nor that in Table I
specifically addressed this mixed pattern of clinical scenario, which is rare. In this type of case, one should go further to look at other clinical patterns such as plasma FSH concentration and testicular size before deciding where the patient should undergo TESA, TESE or MESA. Finally, the factors shown in both protocols for defective spermatogenesis (Table I
) or testicular group (Sharif, 2000
) are merely the predisposing factors to abnormal sperm production and tell you little about the events at molecular level. There is evidence that some of the genetic abnormalities predisposing to male infertility can be transmitted and that they affect treatment outcome (Patrizio et al., 1993
; Koboyashi et al., 1994
; Silber et al., 1998
). A genetic classification of azoospermia focused on its genetic basis would be useful.
What of a genetic classification of azoospermia?
It has been estimated that genetic abnormalities account for up to 30% of the cases of severe male factor infertility (Kupker et al., 1999), most of which present either as azoospermia or oligoasthenoteratozoospermia. Microdeletion of the distal end of the Y chromosome is present in 1320% of men with azoospermia or oligospermia (Reijo et al., 1995
; Pryor et al., 1997
). This region, also called the AZF (the azoospermia factor) region, contains approximately 5x106 base pairs and has been subdivided into three non-overlapping regions AZFa, AZFb and AZFc. A number of candidate genes such as DAZ (deleted in azoospermia), the RBM (RNA-binding motif), DBY (dead box on the Y), DFFRY (Drosophila fatfacet-related Y) and others have been described (Vogt et al., 1998
). The most common microdeletions occur in the AZFc region, which carries active copies of DAZ. The relationship between the candidate genes and their respective AZF sites are well-described (Vogt et al., 1998
). Abnormalities of the candidate genes for spermatogenesis have also been reported in autosomal chromosomes. For example DAZL1 (DAZ-like), a homologous gene to DAZ, is mapped to chromosome 3 in humans. DAZL1 is not identical to DAZ because it has only one sequence repeat of 24 amino acids compared to DAZ with 716 repeats. There have been attempts to classify both fertile and infertile men genetically with regard to their fertility potential. A PCR study of the DNA differences in Japanese men without Y microdeletions have classified men into four groups according to their Y halotypes I, II, III, IV (Kuroki et al., 1999
). Men with halotype II have the lowest sperm count. Others have found that defects in HLA class 1 antigens predispose to idiopathic azoospermia (Miura et al., 1998
). This study shows that the frequency of HLA-A33, B13 and B44 was significantly increased compared with normal controls in Japanese men with idiopathic azoospermia. In support of this study is a report showing differences in HLA class II allele constitution between men with male infertility and normozoospermic men (Van der ven et al., 2000
). Azoospermia may also be due to numerical (e.g. Klinefelter syndrome) or structural chromosomal abnormalities (e.g. translocations) (Chandley et al., 1979
), and genetic mutations in several monogenic conditions such as mitochondria (St John et al., 1997
) or androgen receptor genes (Kupker et al., 1999
). Thus, defective spermatogenesis may be a manifestation of various genetic defects. However, how these genes regulate spermatogenesis is unknown. Genetic diseases also underlie some cases of obstructive azoospermia. Congenital absence of the vas deferens is responsible for at least 6% of cases of obstructive azoospermia and accounts for 12% of cases of infertility in men (Chillon et al., 1995
). Up to 60% of men with congenital absence of the vas deferens have gene mutations in the CFTR gene or 5T allele, a combination of the two being the most common (Chillon et al., 1995
; Kupker et al., 1999
). The genetic defect responsible for Kallmann's syndrome has been defined. It is due to the deletion of KALIG-1 gene, which encodes a protein that is necessary for olfactory and GnRH axonal migration from the olfactory placode to the septalpreoptic nuclei. I anticipate that many more genetic diseases underlying various forms of male infertility will be discovered in future.
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Conclusion |
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References |
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Submitted on April 3, 2000; accepted on July 28, 2000.