Following the availability of genetic studies, vitamin B6-dependent epilepsy, a heterogeneous group of disorders causing seizures that can be controlled or significantly improved by high doses of vitamin B6, including pyridoxine-dependent epilepsy (PDE), pyridox(am)ine-5′-phosphate oxidase (PNPO) deficiency and PLPBP deficiency, was formally diagnosed and treated (10–13). The gene discussed is PNPO; the disease is hyperinsulinemic hypoglycemia, familial, 4.