Association between the c.66A>G variant in the Methionine Synthase reductase and nonsyndromic cleft palate.

Cleft palate (CP) is one of the most frequent congenital malformations in humans. It can occur as part of a syndrome, or, most commonly, be non-syndromic (CPO). There is evidence indicating that both genes and environmental factors are implicated in the etiology of CPO. If on one hand it is well known that maternal smoking, drugs intake and folate deficiency during the first trimester of pregnancy are risk factors for CPO, little is known about genetic susceptibility genes and mechanism causing the failure of the secondary palate to close. Since folate supplementation during periconceptional period and the first trimester of pregnancy have been reported to moderately reduce the chance of having a child with CPO, we used a case-parent triad design to examine whether common variants in genes encoding folate metabolism enzymes are risk factors for CPO. We analyzed 64 complete CPO triads collected in Italy in the 1999-2002 period. All individuals were genotyped for c.677C>T and c.1298A>C variants in the methylene tetrahydrofolate reductase (MTHFR), c.2756A>G variant in the methionine synthase (MTR) gene, and the c.66A>G methionine synthase reductase (MTRR) gene. Association was assessed using transmission disequilibrium test (TDT) and relative risks of variant alleles in mother or child were calculated by log-linear Poisson regression model. While no association was evident for variants in the MTHFR and MTR genes, a highly significant (p=0.0075) excess of transmission of c.66G allele from both parents was found for the MTRR gene variant. Estimated relative risks of CPO in children with one or two copies of c.66G allele was 3.01 (95% C.I. 1.52-5.95) and 3.54 (95% C.I. 1.26-9.94) respectively. Catalyzing the conversion of vitamin B12-dependent MTR enzyme into its active state, MTRR plays a role of paramount importance for the conversion of homocysteine (Hcy) to methionine. Our results for the first time indicate the c.66A>G variant, that is associated with altered levels of blood Hcy, as a possible genetic risk factor for CPO, and suggest that impairment of Hcy remethylation may be a crucial step in the etiology of cleft palate