Xia-Gibbs syndrome (XIGIS; OMIM #615829) is a rare neurodevelopmental disorder caused by de novo heterozygous mutations in the AT-Hook DNA-Binding Motif-Containing 1 (AHDC1) gene (OMIM# 615790) (Xia et al. 2014; Yang et al. 2015; Jiang et al. 2018; García-Acero and Acosta 2017; Ritter et al. 2018; Cheng et al. 2019; Díaz-Ordoñez et al. 2019; Murdock et al. 2019; Yang et al. 2019; Cardoso-Dos-Santos et al. 2020; Gumus 2020; He et al. 2020; Mubungu et al. 2021; Khayat et al. 2021b). Here, AHDC1 is linked to AHDC1-related intellectual disability-obstructive sleep apnea-mild dysmorphism syndrome.