FOLR1 and hyperinsulinemic hypoglycemia, familial, 4: A broad range of differential diagnosis may exist between it and other diseases, such as cerebral folate transport deficiency (FOLR1), dihydrofolate reductase (DHFR) deficiency, methylenetetrahydrofolate reductase (MTHFR) deficiency, hereditary folate malabsorption (SLC46A1), etc. Thus, genetic analysis is required to confirm the diagnosis of MTHFS deficiency.