Of particular importance in the understanding of the molecular, cellular, and clinical manifestations of BRD1 deficiency in humans, it has recently been shown that the BRD1 gene is the only fully contained protein-coding gene in a genomic region (Chr22:49238268–50248907/hg19), that seems critical in the formation of a 22q13.3 large-deletion and Phelan-McDermid syndrome specific genome-wide DNA methylation epi-signature [18]. The gene discussed is BRD1; the disease is Monosomy 22q13.