Abstract
SUPT16H encodes a subunit of the FACT (FAcilitates Chromatin Transcription) complex, a histone chaperone essential for maintaining chromatin integrity during transcription, replication, and DNA repair. Pathogenic de novo SUPT16H missense variants have previously been linked to neurodevelopmental disorders in eight individuals. Here, we expand the genotypic and phenotypic spectrum by identifying 24 additional individuals harboring ultrarare heterozygous missense or truncating variants, who share overlapping clinical features including intellectual disability, autism spectrum disorder, hypotonia, and characteristic craniofacial dysmorphism. To elucidate the underlying mechanisms, we generated a supt16h knockout zebrafish model using CRISPR/Cas9. The supt16h loss-of-function (LOF) model recapitulated key patient phenotypes such as developmental delay, craniofacial anomalies, and hypotonia. Structural and functional analyses of selected SUPT16H variants demonstrated differential rescue of developmental defects in supt16h-deficient embryos, indicating variant-specific LOF effects in vivo. The presence of non-neural manifestations, including facial and ear anomalies, suggested a role for SUPT16H in neural crest development. Consistently, supt16h loss impaired neural crest cell migration and differentiation and triggered p53-dependent apoptosis in the central nervous system (CNS) and neural crest-derived pharyngeal arches. Notably, supt16h deficiency impaired oligodendrocyte specification in the CNS and perturbed differentiation of neural crest-derived Schwann cells in the peripheral nervous system, providing a plausible basis for hypotonia. These findings uncover a previously unrecognized role of SUPT16H in neural crest development, linking chromatin regulation to neural crest-derived lineage specification and differentiation, thereby defining SUPT16H deficiency as a neurocristopathy that broadens the clinical and mechanistic landscape of SUPT16H-associated disorders.