A third patient with RAP1B-related syndromic thrombocytopenia and novel clinical findings

RAP1B is a member of the RAS family of small GTP binding proteins (GTPases), activated in many signal transduction pathways regulating numerous cellular processes including proliferation, adhesion, and migration. RAP1B-related syndromic thrombocytopenia is an ultra-rare genetic disorder characterized by hematologic abnormalities, neurodevelopmental delays, and congenital birth defects. Initial report of a germline RAP1B variant described a patient with a Kabuki syndrome-like phenotype due to RAP1B loss-of-function.