Among >270 individuals diagnosed with Xia-Gibbs syndrome (XGS; MIM: 615829), almost all have de novo “truncating” mutations in AHDC1. There are now also 10 reports of XGS arising from de novo missense AHDC1 mutations. Here, AHDC1 is linked to AHDC1-related intellectual disability-obstructive sleep apnea-mild dysmorphism syndrome.