Classically, patients with PNPO deficiency present in infancy and their epilepsy does not respond to pyridoxine, but the phenotypic spectrum of PNPO deficiency is expanding as there are documented cases of PNPO deficiency with delayed onset or response to pyridoxine (rather than PLP), suggesting that clinicians need to keep an eye open for atypical presentations of this epilepsy (12). The gene discussed is PNPO; the disease is epilepsy.