Dihydrofolate reductase (DHFR) 19-bp ins/del polymorphism and methylenetetrahydrofolate reductase (MTHFR) C677T in coronary heart disease patients: potential intracellular folate unbalancing.

Elevated homocysteine (Hcy) due to common gene variants is correlated with coronary heart disease (CHD), but definite causality remains uncertain. Hcy increases due to genetic and environment interactions. Assuming no direct effects of folate on CHD except via increased Hcy, and that folate drives Hcy metabolism, investigating on how genes influence folate balancing is strongly useful. DHFR and MTHFR fully activate diet folate. Common polymorphisms influence activity/level of enzymes. MTHFR677TT reduces enzyme efficiency yielding ~20% higher Hcy. Less definitive is the role ascribed to DHFR 19bp ins/del; some authors reported ~50% higher mRNA in del/del genotype. We selected 14 CHD patients from our Center carrying opposite DHFR/MTHFR genotypes. We hypothesized that patients (n=7) carrying both polymorphisms in homozygous condition (DHFRdel/del and MTHFR677TT) might have different folate status and respond differently, than double wildtypes (n=7), under controlled in vitro folate levels. So, we put whole blood in culture (t0, t48, t96-120 hours) containing 10ng/ml folate. DD/TT patients had significant lower basal folate levels (plasma and RBC) versus wildtypes. Interestingly, in vitro culture showed DD/TT genotype rapidly gained folate stores, to completely cancel the gap at ~96h. These results are partially in contrast with previous reports in which DHFR properties were tested without consider MTHFR, and strongly advice to analyze these two common variants before ascribing disease risk and public health implications.