Members of the WD repeat protein family are involved in a variety of cellular processes, including cell cycle progression, signal transduction, apoptosis and gene regulation. BRWD3 (bromodomain and WD repeat-containing protein 3) is a 1,802 amino acid protein expressed in fetal liver and most adult tissues. Existing as five alternatively spliced isoforms, BRWD3 contains two bromo domains, nine WD repeats and is thought to play a role in transcription by modifying chromatin. Mutations in the gene encoding BRWD3 are the cause of mental retardation X-linked type 93 (MRX93), which is also known as mental retardation X-linked with macrocephaly (XLMR). MRX93 is characterized by mild intellectual disability, macrocephaly, a prominent forehead and large cupped ears.