In addition to mutations in the coding exons of AHDC1 associated with Xia-Gibbs syndrome, Yang et al. recently described two additional ones in the 5′ UTR of AHDC1 (c.-88 C > T and c.-781 C > G) in patients with obstructive sleep apnea, one of the clinical manifestations of XIGIS (Yang et al. 2019) (Table 1). The gene discussed is AHDC1; the disease is AHDC1-related intellectual disability-obstructive sleep apnea-mild dysmorphism syndrome.