KAT6B and Global developmental delay: Say-Barber-Biesecker-Young-Simpson syndrome (SBBYSS, OMIM#603736) and genitopatellar syndrome (GTPTS, OMIM#606170), characterized by global developmental delay/intellectual disability and special clinical manifestations, are two distinct clinically overlapping syndromes caused by truncating sequence variants in the <i>KAT6B</i> (10q22.2) gene.