This aligns with previous studies of this region that show that mouse Twist1 regulatory regions can be found within both introns and exons of the Hdac9 gene.49 51 57 Notably, a 23 kb deletion that included three of these regulatory element sequences, which may also be bound by craniofacial transcription factors Lmx1b and Tfap2, was associated with a reduction in Twist1 expression.51 Furthermore, rearrangements that leave the gene intact but remove regions telomeric of TWIST1 lead to Saethre-Chotzen syndrome (SCS),58–61 which is caused by TWIST1 haploinsufficiency. The gene discussed is TFAP2A; the disease is Saethre-Chotzen syndrome.