Background: Cândido Godói (CG) is a small city in South Brazil in which natural twin births (both monozygotic and dizygotic) occur at an unusually high rate and the twin trait runs through the local families, which are mostly European descendants. We have argued that a genetic founder effect must have occurred during the settlement of CG and that genetic factors may help to explain the familial aggregation of twinning in that city.Objective: The aim of this study was to evaluate single nucleotide polymorphisms (SNPs) related to folliculogenesis (rs6166:C > T in FSHR, rs11031006:G > A near FSHB, and rs17293443:T > C in SMAD3) and successful pregnancies (rs2010963:C > G in VEGFA, rs1800629:G > A in TNF, rs1801131:T > G and rs1801133:G > A in MTHFR) in mothers from CG.Study design: Forty-four mothers of twins (the case group) and 102 mothers of singletons (the control group) from CG were investigated. Genotypes were determined using real-time PCR (TaqMan® SNP Genotyping Assay).Results: For all SNPs, the distributions of the genotypic and allelic frequencies were similar between cases and controls. Interestingly, a deviation from the Hardy-Weinberg equilibrium was detected for SNP rs11031006:G > A near FSHB in the control population. Different combinations of risk alleles and haplotypic analyses were homogeneously distributed between cases and controls.Conclusion: These results suggest a lack of association between the seven studied SNPs and twin births in CG. However, we hypothesized that other genetic variants related to folliculogenesis or successful pregnancies may be involved in this phenomenon. Identifying such genetic components may be important not only for the Brazilian "Twins' Town" but also for a better understanding of twinning in general.
Keywords: Fertility; founder effect; reproduction; single nucleotide polymorphism; twinning.