Patient-specific zebrafish models reveal a complex phenotypic spectrum in NBAS-associated atypical osteogenesis imperfecta.

Neuroblastoma amplified sequence gene (NBAS) variants are associated with short stature, optic atrophy, and Pelger-Huët anomaly (SOPH) syndrome. We previously identified compound heterozygous variants in NBAS to cause atypical Osteogenesis Imperfecta (OI), with these patients presenting with short stature, developmental delay, and recurrent long-bone fractures. However, skeletal disease progression due to these variants and the disease mechanisms underlying NBAS-associated OI remain poorly understood. Here, we provide a clinical update on previously identified patients and investigate the role of NBAS during skeletal development using zebrafish knockout and patient-specific missense variant zebrafish models. Homozygous knockout larvae exhibited delayed operculum development, reduced bone ossification, and defects in Meckel's cartilage morphology and its underlying cellular structure. Homozygous missense larvae displayed milder cartilage defects without any major defects to early skeletal structures. Seemingly opposing phenotypes were observed in compound heterozygous zebrafish carrying the knockout and missense alleles in trans, with no obvious phenotypes seen in the Meckel's cartilage and accelerated operculum development observed. Together, our results demonstrate that different nbas variants differentially affect skeletal development, suggesting complex spectrums of phenotypic and pathogenic mechanisms in NBAS-associated atypical OI.