Among the 24 patients with adolescent/adult onset MTHFR deficiency, 12 patients suffered from epilepsy (50%), with different epileptic syndromes: generalized tonic clonic seizures (n = 4), focal seizures (n = 3), absence seizures (n = 1), juvenile myoclonic epilepsy (JME) then progressive myoclonic epilepsy (PME) (n = 1), and not documented in other patients (n = 3). The gene discussed is MTHFR; the disease is Progressive myoclonic epilepsy.