Regarding androgens it is known that they are also essential
Regarding androgens, it is known that they are also essential for reproductive success (Walters et al., 2010). At the molecular level, their effects are produced mainly by dihydrotestosterone (DHT), arising from the conversion of testosterone by the enzyme 3-oxo-5-alpha-steroid-4-dehydrogenase (encoded by the SRD5A2 gene) and through the activation of androgen receptors. Studies in animal models have found an association between the deficiency of this enzyme and fetal loss (Mahendroo et al., 1997). However, the role of SRD5A2 in human pregnancy remains to be elucidated. The polymorphism rs523349 is a C/G functional variant within SRD5A2, corresponding to a missense mutation in codon 89 (valine to leucine, respectively). It has been reported that the enzyme transcribed with the leucine allele exhibits a lower conversion rate of testosterone to DHT (Beesley et al., 2007). Therefore, we propose that polymorphism is a candidate variant to influence miscarriage.
The aim of this study, using human fetal tissue samples, was to map the impact of eight polymorphisms in three genes involved in sex hormone metabolism (ESR1, CYP19A1 and SRD5A2) in order to elucidate their role in idiopathic miscarriage.
Materials and methods
Results From the 94 miscarriage samples, 14 failed the initial quantitative fluorescence-PCR VX765 analysis due to low DNA quality and they were therefore excluded from the study. Among the remaining 80 samples we detected 13 (16.25%) aneuploidies, which were found either <12 gestation weeks (n = 11) or between 12 and 24 weeks (n = 2). This increase in chromosomopathies among miscarriage in the first trimester was significant (P = 0.0013, chi-squared test) and concordant with previously reported results (Botella and Clavero-Nuñez, 1986). The most frequent chromosomopathy found was chromosome 21 trisomy (n = 7) followed by triploidies (n = 5) and one trisomy for chromosomes 15 and 16, respectively. As previously mentioned, only those euploid case samples (n = 67) were considered for further analysis. Genotype frequencies in the case and the control groups for the eight genetic polymorphisms under study are shown in . Control population fits HWE for all SNPs. Miscarriage euploid case samples showed a statistically significant excess of heterozygotes (rs10046 and rs2234693 with HWE P-values of <0.001 and 0.022, respectively) and defect of heterozygotes (rsrs9282858 and rs9340799 with HWE P-values of 0.046 and 0.031, respectively). Only those variants with HWE P-value >0.05 were considered for the case–control study. As shown in , the SRD5A2 rs523349 allele G exhibited a significant increased frequency among cases (0.25 vs 0.53, P = 1.745 × 10–9, chi-squared test). Subjects harbouring the G (Leu) allele presented a significant increased risk of undergoing SA either in heterozygosity (OR = 5.615) or in homozygosity (OR = 11.245). According to the Akaike information criterion, the best-fitting genetic model of inheritance was the additive one (AIC = 294.1). Next, we evaluated the role of SRD5A2 rs523349 in the risk of miscarriage, taking the week of miscarriage as a quantitative output. As shown in , 50% of the samples with rs523349 C/C (Val/Val) genotype underwent miscarriage at week 10.00 ± 0.58 (mean ± SE), in contrast to the C/G (Val/Leu) and G/G (Leu/Leu) samples, which exhibit a 50% survival score of 16.00 ± 1.09 and 14.00 ± 2.37 weeks, respectively. This effect was particularly evident among female fetuses (). Interestingly, when the time to miscarriage was stratified according to fetal sex (23 males and 44 females), we observed that female fetuses tend to undergo miscarriage later than males (P = 0.037, Mann–Whitney test) (), indicating that miscarriage differentially affects male and female fetuses.
Discussion The role of the hormone system in embryonic development and fetal viability is essential. We proposed that common genetic polymorphisms directly involving sex hormone metabolism can cause variations in hormone balance with a clear impact on fetal viability. In the present study we found an association between SRD5A2 rs523349 polymorphism and the risk of idiopathic miscarriage. It is interesting to note that most of the current studies focused on this topic have been conducted in women with recurrent pregnancy loss and only few studies have performed genetic analysis on the fetal tissue (Bae et al., 2007; Callejon et al., 2007). Our results showed a strong association between the G allele of rs523349 and the risk of miscarriage. This association was significant in both the heterozygous and the homozygous genotypes, concordant with a dominant additive genetic model. When regression studies were performed, we observed that the nature of this association was more evident in the second trimester miscarriage and, in principle, particularly constrained to the female group. However, the reduced sample size of the male sub-series compromised the statistical power of this subgroup.