Frequency of CFTR gene mutations in males participating in an ICSI programme: Brief communication
S. Jakubiczka1,
Th. Bettecken1,
M. Stumm1,
I. Nickel2,
J. Müsebeck1,
P. Krebs1,
Ch. Fischer3,
J. Kleinstein2 and
P. Wieacker1,4
1 Institut für Humangenetik, Otto-von-Guericke-Universität, Leipziger Str. 44, D-39120 Magdeburg,
2 Klinik für Reproduktionsmedizin und Gynäkologische Endokrinologie, Otto-von-Guericke-Universität, Magdeburg, and
3 Institut für Humangenetik, Ruprecht-Karls-Universität, Heidelberg, Germany
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Abstract
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A higher prevalence of cystic fibrosis transmembrane regulator (CFTR) gene mutations has been suggested both in men affected by congenital aplasia of the vas deferens, and in individuals presenting with reduced sperm quality. In this case, an increased risk for offspring being affected by cystic fibrosis (CF) can be expected in couples who are planning to undergo intracytoplasmic sperm injection (ICSI), since most of the male partners suffer from infertility. In order to determine the risk for these couples more precisely, we offered them a test for the most frequent CF mutations prevalent in the German population. The frequency of mutations within the CFTR gene in the female group was in the same range as expected for the general population (six out of 150). In 10 out of 207 males tested, infertility could be explained by exogenous factors not related to CFTR. Among the remaining 197 males with idiopathic infertility, we detected 13 heterozygotes for a mutation within the CFTR gene. This slightly, but significantly (P = 0.014), elevated rate could indicate that infertile males have, compared with the general population, an increased risk of being a carrier of a CFTR gene mutation.
Key words:
CAVD/CFTR mutations/cystic fibrosis/ICSI/male infertility
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Introduction
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In a recent report, it has been suggested (van der Ven et al., 1996
) that there is a higher prevalence of cystic fibrosis transmembrane regulator (CFTR) gene mutations in otherwise healthy men presenting with reduced sperm quality as compared with controls with normal sperm parameters. If this holds, the risk for subfertile males of having offspring affected by cystic fibrosis (CF) should be elevated. The wide majority of males in couples planning to undergo intracytoplasmic sperm injection (ICSI) have reduced fertility. So far, the follow-up of children born after ICSI has been very limited. For determining more precisely the risk for these couples of having offspring affected by CF, screening for CFTR mutations was offered additionally to chromosome analysis and a test for deletion of the deleted in azoospermia (DAZ) region.
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Materials and methods
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CFTR screening included the most frequent CFTR mutations in the German population (R347P,
F508, G542X, S549I,N,R(A
C), G551D, R553X, N1303K, and 3849+10kbC
T) (Dörk et al., 1994
) as well as the mutation R117H and the analysis of the IVS8-T haplotype. Both, R117H and the splice variant IVS8-5T are frequently found in males affected by congenital bilateral or congenital unilateral absence of the vas deferens (CBAVD/CUAVD) (e.g. Casals et al., 1995
; Chillon et al., 1995
; Dörk et al., 1997
).
The influence of the CFTR gene product on fertility is not yet understood. Since an effect of the CFTR protein on female fertility could not be ruled out, females were initially included in our study as well. Nearly all couples who were offered the test agreed to participate in our study. In the first phase of this study 150 couples, and in the second phase another 57 infertile males, were tested prior to ICSI.
CBAVD was excluded in all males. CUAVD was confirmed in one patient. In all but 22 males who refused examination, screening for a deletion in the DAZ region was carried out. Four males (including one with an isochromosome Yp) showed deletions of the DAZ region. Chromosome aberrations were found in two further males [45XYder(13;15) (q10;q10); 46XYt(7;13) (p11.2;p11.2) ]. In 4 males, the most likely cause of infertility was chemotherapy in the past. Taken together, in 10 of the 207 males tested, infertility could be explained by exogenous causes or genetic factors not related to CFTR. Thus, 197 males with idiopathic infertility remained in the study.
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Results
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The results of CFTR mutation testing are shown in Table I
. The incidence of CF in the Caucasian population is estimated to be 1 in 2000 (Vogel and Motulsky, 1996
), from this a frequency of heterozygosity of 1 in 22.4 can be derived. The mutation detection rate in our study was ~82% (Dörk et al., 1994
). With these assumptions one CF mutation in 27.3 (0.037) individuals should be expected. Among our group of 197 infertile males we found 13 CF-heterozygotes, indicating a frequency of heterozygosity of 1 in 15.2 (0.066) for idiopathic infertile males. The difference in heterozygote frequency between males with idiopathic infertility and the general population was significant (P = 0.014; one-sided exact binomial test; Statistical Analysis System Version 6.1 on PC; Cytel Software Corporation, Cambridge, MA, USA). It is unlikely that this difference can be attributed to unrecognized cases of CBAVD or CUAVD because the frequency of IVS8-5T alleles was not elevated.
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Table I. Frequency of CFTR mutations in 197 males affected by idiopathic infertility and 150 of their female partners
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Discussion
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It is remarkable that the frequency of CFTR mutations in the males tested (van der Ven et al., 1996
) is about three times higher than in our patients. The most obvious difference between the studies lies in the frequency of the mutation G542X, accounting for eight out of 18 mutations detected among 101 males by van der Ven et al. (1996) but not found in any of our probands. A possible explanation could be a different ethnic origin of the tested populations. In another study (Pauer et al., 1997
) 51 infertile males without CBAVD for mutation
F508 were tested. Only one of these was heterozygous. This low rate of heterozygosity may be attributed to the larger statistical error associated with the smaller sample size.
In our group of 150 females tested, six CF mutations were found. This frequency of heterozygosity for CFTR mutations (1 in 25, 0.04) is in the same range as for the general population (95% confidence interval, 0.020.9; Statexact, Version 2 for DOS; Cytel Software).
Several authors have discussed a reproductive advantage for CF heterozygotes. Recent studies did not support this theory (de Vries et al, 1995
; Dahl et al., 1998
). From the data of van der Ven et al. (1996) and our study, a slight reproductive disadvantage for heterozygous males should be expected. In summary we conclude that, according to our data, infertile males might have an elevated risk of being carriers of a mutation within the CFTR gene, as compared to the general population. Therefore, we recommend CFTR mutation testing in males with idiopathic infertility prior to invasive reproduction techniques. If any CF mutation is detected in a patient, CFTR screening should be offered to the female partner.
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Notes
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4 To whom correspondence should be addressed 
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References
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Casals, T., Bassas, L., Ruiz-Romero, J. et al. (1995) Extensive analysis of 40 infertile patients with congenital absence of the vas deferens: in 50% of cases only one CFTR allele could be detected. Hum. Genet., 95, 205211.[ISI][Medline]
Chillon, M., Casals, T., Mercier, B. et al. (1995) Mutations in the cystic fibrosis gene in patients with congenital absence of the vas deferens. N. Engl. J. Med., 332, 14751480.[Abstract/Free Full Text]
Dahl, M., Tybjaerg-Hansen, A., Wittrup, H.H. et al. (1998) Cystic fibrosis
F508 heterozygotes, smoking, and reproduction: studies of 9141 individuals from a general population sample. Genomics, 50, 8996.[ISI][Medline]
de Vries, H.G., Collée, J.M., Meeuwsen, W.P. et al. (1995) Number and sex of offspring of
F508 carriers outside cystic fibrosis families. Hum. Genet., 95, 575576.[ISI][Medline]
Dörk, T., Mekus, F., Schmidt, K. et al. (1994) Detection of more than 50 different CFTR mutations in a large group of German cystic fibrosis patients. Hum. Genet., 94, 533542.[ISI][Medline]
Dörk, T., Dworniczak, B., Aulehla-Scholz, C. et al. (1997) Distinct spectrum of CFTR gene mutations in congenital absence of vas deferens. Hum. Genet., 100, 365377.[ISI][Medline]
Pauer, H.U., Hinney, B., Michelmann, H.W. et al. (1997) Relevance of genetic counselling in couples prior to intracytoplasmic sperm injection. Hum. Reprod., 12, 19091912.[Abstract]
van der Ven, K., Messer, L., van der Ven, H. et al. (1996) Cystic fibrosis mutation screening in healthy men with reduced sperm quality. Hum. Reprod., 11, 513517.[Abstract]
Vogel, F. and Motulsky, A.G. (1996) Human Genetics. 3rd edn. Springer-Verlag, Berlin, Heidelberg, New York, pp. 597.
World Health Organization (1992) Laboratory Manual for the Examination of Human Semen and SpermCervical Mucus Interaction. 3rd edn. Cambridge University Press, Cambridge, UK.
Submitted on December 15, 1998;
accepted on March 18, 1999.