AHDC1 and AHDC1-related intellectual disability-obstructive sleep apnea-mild dysmorphism syndrome: De novo stop-gain and frameshift mutations in the gene encoding the AT-Hook DNA-Binding Motif-Containing 1 (AHDC1) protein that are predicted by conceptual translation to lead to truncated AHDC1 protein synthesis are well-established as an underlying cause of Xia-Gibbs syndrome (XGS; MIM: 615829).1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 Reported truncating mutations span most of the length of the protein and include some sites of recurrent, independently arising de novo events.