Genitopatellar syndrome (GTPTS; MIM 606170) is a rare autosomal dominant disorder characterized by hypoplastic or absent patella and genital abnormalities.  Other common features include microcephaly, mental retardation, agenesis of the corpus callosum, joint contractures, club feet, renal anomalies and coarse facial features.  Cardiac defects are seen in some patients.  GTPTS is caused by mutations in KAT6B, which encodes lysine acetyltransferase 6B, a histone modifying enzyme involved in gene regulation.  All currently reported GTPTS mutations are nonsense or frameshift changes localized to the last exon of KAT6B (exon 18).  Mutations in KAT6B also cause Ohdo syndrome, SBBYS variant (SBBYSS; MIM 603736), a clinically distinct disorder with some overlapping features.