subjects (P < 0.001). The frequency of homozygosity for the mutation in the different groups studied ranged from 4% to 23%. In the healthy cohort, the frequency was 16.2%. The allele frequencies of the thermolabile allele were 38.5 and 27.3 in young and old controls, and 37.3 and 33.3 in CAD and PAOD patients. In healthy younger subjects, the mutant allele was 14 times more frequent compared to the older subjects (P < 0.001). No difference in either MTHFR genotype distribution (P = 0.33) or allele frequencies (P = 0.48) between patients and controls was found. Except for the PAOD group with elevated tHcy levels for carriers compared to other genotypes, no statistically significant difference was found comparing homocysteine levels with genotype.

This study shows no link between the mutation and the occurrence of vascular disease, but we found evidence pointing to a correlation between the mutation and longevity in our population. Elevated fasting levels of total homocysteine are now accepted as an independent risk factor for the development of arteriosclerotic vascular diseases. A polymorphism in the gene encoding methylenetetrahydrofolate reductase (MTHFR), caused by the C677T point mutation, leads to increased thermolability of the enzyme with reduced enzyme activity. We studied the frequency of this mutation in different groups of the Swiss adult population.

In conclusion, while there is a clear association between the occurrence of the mutation and tHcy levels, so far, there is no conclusive evidence that homozygosity for C677T itself is a risk factor for vascular disease. The emerging picture is one of a high frequency of the polymorphism in all populations, but no conclusive evidence that it is a risk factor for vascular disease.trend towards a lower frequency of the homozygous MTHFR C677T genotype in the elderly population was observed in our study. The substitution was common in all groups, with an overall allele frequency of 27-33%. There was no significant difference in allele frequencies between patients and controls, except for a significant difference between the young and elderly control groups, and between the elderly control group and CAD patients. The MTHFR genotypes followed the Hardy-Weinberg equilibrium in all groups except for the PAOD group. 

No statistically significant difference was found when comparing gender, when comparing the four different groups, or when cases (PAOD and CAD) and controls (young and elderly) were compared with each other. As folate values were not available in all groups, subjects were divided into those with tHcy levels above or below the median values. A tHcy level above the median might serve as a marker for low folate status and allow testing of the genotype-cardiovascular link. No differences in genotype distributions between high and low tHcy groups were found, confirming the lack of such a link in our study.

The Hcy levels were significantly different between all groups, with a clear increase with age. Although the mean age of the elderly healthy group and the PAOD patients was comparable, the Hcy increase was even more pronounced in the latter group compared to the young controls. The difference of MeTHF values between the two groups in which MeTHF was determined was statistically significant. 

A statistically significant difference of tHcy values was found between different genotypes within the PAOD group but not in other groups. The lack of correlation between genotype and tHcy levels raises questions about whether differences in folate status are responsible for contradictory findings in relationships between thermolabile MTHFR genotype and vascular disease.

There was no direct association found between the thermolabile MTHFR genotype and disease. The reduced frequency of the homozygous MTHFR C677T genotype in elderly and PAOD groups indicates an age-associated decrease in the prevalence of the mutation, which may indicate a lower life expectancy for individuals homozygous for the mutation. However, the cause of this lower life expectancy remains open, as there is no direct association between the thermolabile MTHFR genotype and disease.Shift could possibly explain the difference seen between young and old controls. In conclusion, tHcy concentrations are not consistently related to the mutant allele, at least in subjects with adequate folate intake. Therefore, the possibility that the reduced frequency of the C677T allele with increasing age is not directly related to Hcy-induced vascular morbidity or mortality needs evaluation. Finally, this study reinforces the lack of a link between the presence of homozygosity for the mutation and the occurrence of vascular disease shown in the majority of previous studies.

Acknowledgement
This study was supported in part by a grant from the Swiss National Science Foundation (No. 324598895). Furthermore, Anderson et al. [23] observed no increased risk for myocardial infarction in subjects above 60 years of age with the / genotype, in contrast to subjects below 60 in whom an increased risk was found. This could indicate a lower frequency of the / genotype in elderly subjects also in this study. Although none of these findings showed high statistical significance, age-dependency may have contributed also to the results of Deloughery et al. and van Bockxmeer et al. [21,45], where a lower incidence of the / genotype was observed in the older patient group compared to younger controls.

Thus, the data available so far comparing older and younger groups allow no definite conclusion to be made, and further studies focusing on whether the homozygous status for C677T has an impact on life expectancy, particularly prospective studies, are needed.