Human Reproduction, Vol. 19, No. 1, 65-70,
January 2004
© 2004 European Society of Human Reproduction and Embryology
Frequent polymorphism of the mitochondrial DNA polymerase gamma gene (POLG) in patients with normal spermiograms and unexplained subfertility
1 Department of Growth and Reproduction, Copenhagen University Hospital (Rigshospitalet), DK-2100 Copenhagen, 2 Department of Biostatistics, University of Copenhagen, DK-2200 Copenhagen, 3 Fertility Clinic, Rigshospitalet, DK-2100 Copenhagen and 4 Department of Environmental Medicine, University of Southern Denmark, DK-4000 Odense, Denmark The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors
5 To whom correspondence should be addressed at: Department of Growth and Reproduction, Section GR-5064, Copenhagen University Hospital (Rigshospitalet), Blegdamsvej 9, DK-2100 Copenhagen, Denmark. e-mail: erm{at}rh.dk
BACKGROUND: Male fertility largely depends on the quality of sperm production, which may be affected by environmental and genetic factors. In this study, we explored a possible role of the polymerase gamma (POLG) gene polymorphism, recently reported to be associated with male infertility in some populations. METHODS: The polymorphic CAG repeat (usually 10 codons long) in the POLG gene was studied in 1298 male subjects: 429 patients with infertility/subfertility, and 869 controls (495 men from the general population with unknown fertility and 374 recent fathers). In all subjects, the POLG polymorphism was assessed in relation to their semen quality, and—in the fertile controls—with biological fecundity measured as waiting time-to-pregnancy (TTP) for the couples. In the patients lacking the common POLG allele, the outcome of the assisted reproductive techniques (ART) for the couples was evaluated. RESULTS: The absence of one (10/
10) or both common POLG alleles (10/10) was more frequent among the subfertile patients than among fertile controls (P = 0.021 and P = 0.04 respectively). The estimated predictive value for infertility in a man homozygous for the POLG polymorphism was 15.5% (95% CI: 4.8–51%). There was a positive association with sperm concentration: 14.3% of the normospermic subfertile patients were homozygous for the absence of the common POLG allele (10/10), in comparison with 2.3% of unselected controls (P = 0.001) and 0.9% of the fertile men (P = 0.0001). No association with sperm motility, morphology and TTP was found. Spermatozoa of the three 10/10 patients treated with IVF retained the ability to penetrate the egg, but the fertilization rate was low. Nine homozygous 10/10 patients were treated with ICSI, resulting in pregnancy in seven couples. CONCLUSIONS: The POLG gene polymorphism should be considered as a possible contributing factor in patients with unexplained subfertility and normal spermiograms. The oocyte penetration ability of sperm may be partially impaired in the 10/10 patients but most of them can be successfully treated with ICSI.
Key words: gene polymorphism/male infertility/mitochondrial DNA/sperm quality/POLG gene
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