Definition:

Say-Barber-Biesecker-Young-Simpson syndrome (SBBYSS), also referred to as the Say-Barber-Biesecker variant of Ohdo syndrome, is a rare multiple anomaly syndrome characterized by severe intellectual disability, blepharophimosis, and a mask-like facial appearance. A number of individuals with SBBYSS also have thyroid abnormalities and cleft palate. In 1986, Ohdo described two siblings and their cousin with blepharophimosis, ptosis, congenital heart defects, intellectual disability, and hypoplastic teeth. Subsequently, the Young-Simpson syndrome was described. Later the Young-Simpson syndrome was renamed the Say-Barber-Biesecker-Young-Simpson (SBBYS) variant of Ohdo syndrome. SBBYSS and genitopatellar syndrome (GPS) [DS:H01794] are clinically similar disorders with some overlapping features. They were found to be caused by de novo truncating sequence variants in the KAT6B (histone acetyltransferase) gene, strongly suggesting that they are allelic disorders.