The number of dichorionic twin pregnancies is reduced by the common MTHFR 677C→T mutation

Abstract

In multiple pregnancies, demands for folic acid are considerably increased. The most common inborn error of folate metabolism is mild methylenetetrahydrofolate reductase (MTHFR) deficiency due to the synthesis of a thermolabile variant of the enzyme with impaired catalytic activity which leads to reduced 5-methyltetrahydrofolate (5-methyl-THF) and mildly elevated homocysteine plasma concentrations when folate status is inadequate. To investigate whether the number of offspring is influenced by this mutation, we determined the frequency of the 677C→T substitution in 156 singleton and 40 twin mothers with dichorionic placentation. The T allele frequency in singleton (0.30) and twin mothers (0.16) was significantly different (P = 0.011). Mothers with the 677C→T mutation had a 2.28 times lower risk of having a twin pregnancy than those without (95% confidence interval = 1.18–4.66; P = 0.008). Our observation would explain, at least in part, the hereditary trait of multiple gestations and is in agreement with the ethnic distribution pattern of the T allele which has been found to be inversely correlated with the incidence of dichorionic twins. Our findings suggest that the MTHFR 677C→T mutation interferes with human brood size, probably by influencing the proliferation of rapidly dividing embryonic and maternal cells.