For the mild form of MTHFR deficiency, there are two main alleles: C677T and A1298C both of which have been studied through population frequency analysis. The C677T mutation is an alanine®valine substitution resulting in a thermolabile form of the enzyme that was found in 17% of 212 North American coronary artery disease patients; Rozen, 1996. Its allele frequency (as well as the frequency of C677T homozygosity) shows tremendous regional and ethnic variation. (Click Here to see figures) For whites in Europe, the homozygosity frequency ranged from 8% in Germany to 18% in Italy, while Britain and Ireland were intermediate at 13% and 11% respectively. For non-European whites, the range was from 10 to 14% for homozygosity, but allele frequency is estimated to be as high as 35-40% in French Canadians and North Americans specifically (Frosst et al 1995). In addition, Hispanics also seem to have a higher frequency of the allele, as demonstrated by a sample from California with a rate of 21% homozygosity. Conversely, in a study from sub-Saharan Africa, the allele frequency was consistently found to be 7%. The homozygosity of the allele frequency for non-African blacks is even lower with estimates of 1-2%. A sample of Asians studied was found to have an 11% homozygosity frequency, while Amerindians varied from 21% (sample in Brazil) to 1% (Tupi Parakana tribe). Nevertheless, most studies reveal that there is no correlation between a particular gender and this allele (hence, reaffirming that the disease is autosomal). However, it was found to be slightly more prevalent in younger generations than in older people. 

As for the A1298C allele, there was an approximate frequency of homozygosity of 9% among control subjects. Heterozygous C677T/A1298C Canadians had a 15% frequency, while it was 17% in the United States and 20% in the Netherlands. In addition to these two alleles, the T1059C allele has also been linked to the disorder, but it not recognized as an important allele, because it is a silent mutation. Therefore, few researchers have studied it, but it has been reported to have an allele frequency of 85%. This silent mutation is typically co-transmitted with the A1298C allele. (Botto and Yang, 2000)