Known confounders of folate status such as vitamin B12 deficiency and genetic variations influencing folate metabolism (i.e. methylenetetrahydrofolate reductase (MTHFR) and dihydrofolate reductase (DHFR) polymorphisms) should be included in the recruitment criteria, or at least captured (8). The gene discussed is MTHFR; the disease is vitamin B12 deficiency.