Xia-Gibbs syndrome (XGS; MIM: 615829) is a phenotypically heterogeneous neurodevelopmental disorder (NDD) caused by newly arising mutations in the AT-Hook DNA-Binding Motif-Containing 1 (AHDC1) gene that are predicted to lead to truncated AHDC1 protein synthesis. The gene discussed is AHDC1; the disease is AHDC1-related intellectual disability-obstructive sleep apnea-mild dysmorphism syndrome.