MTHFR and biotinidase deficiency: Seizures are common features of various cofactor metabolic disorders including pyridoxine-dependent epilepsy, pyridoxal phosphate-responsive epilepsy, early-onset vitamin B6-dependent epilepsy, cerebral folate deficiency, methylenetetrahydrofolate reductase (MTHFR) deficiency, molybdenum cofactor deficiency, biotinidase deficiency, and holocarboxylase synthetase deficiency (Table 1).