MTHFR and Abnormal heart morphology: In support of the null findings in the present birth cohort study from Norway and Denmark, in particular for conotruncal defects, is a report using a Mendelian randomization approach that genotyped >3000 individuals with conotruncal defects for the variants in the MTHFR (methylenetetrahydrofolate reductase) gene.45 The variant 677TT has previously been found to be associated with reduced folate levels in blood and could be associated with offspring risk of heart defects.