Pathogenic variants in one allele of the <i>KAT6A</i> gene encoding the histone acetyltransferase KAT6A (MOZ, MYST3) cause Arboleda-Tham syndrome (ARTHS), characterised by developmental delay, cognitive impairment, and autism-like behaviours. The gene discussed is KAT6A; the disease is autosomal dominant intellectual disability-craniofacial anomalies-cardiac defects syndrome.