Missense germline mutations of ATP6AP1 have been shown to be causative of Immunodeficiency 4720, characterized by hepatopathy, cognitive impairment, and abnormal protein glycosylation, whereas missense germline mutations affecting ATP6AP2 result in the Hedera-type X-linked mental retardation syndrome21,22. The gene discussed is ATP6AP2; the disease is Cognitive impairment.