Summary
A recently described mutation in the methylenetetrahydrofolate reductase (MTHFR) gene
(a C to T transition at nucleotide 677) is associated with a thermolabile phenotype
and decreased enzyme activity. In homozygotes, the mutation is also related to hyperhomocysteinemia
and increased risk for atherosclerotic disease and (apparently) venous thrombosis.
The prevalence of this mutation in different human populations is unknown. We have
investigated the frequency of the 677 C→T mutation in the MTHFR gene in 337 individuals
(674 chromosomes) belonging to four ethnic groups: Whites, African and Brazilian Blacks,
Asians and Amerindians. The frequencies of the positive allele among Whites and Asians
were similar to those previously reported for Caucasian populations. The positive
allele seems to be slightly rarer among the Amerindians (frequency 24.0%) in comparison
to Whites and Asians, with a heterogeneous distribution among the five Indian tribes
analysed. In contrast, the mutation has a very low prevalence in Blacks, especially
among the African Blacks, for whom the mutation was absent in homozygosity. Our data
indicate that the 677 C→T MTHFR mutation has a significantly heterogeneous distribution
among different ethnic groups, a fact that may contribute to explain geographical
or racial differences in the risk for vascular disease.
