7096 Variants in WASHC3, a component of the WASH complex, cause distinctive facial dysmorphism, short stature, and variable neurodevelopmental abnormalities

Abstract Disclosure: Y. Jee: None. J. Lui: None. D. Marafi: None. Z. Xia: None. R. Bhatia: None. E. Zhou: None. I. Herman: None. A.G. Temnycky: None. P. Whalen: None. G. Elliot: None. E. Leschek: None. R. Wijngaard: None. R. Beek: None. A. Vreugd: None. M. De Vries: None. C. Karnebeek: None. M. Oud: None. T. Markello: None. K. Barnes: None. H. Alrohaif: None. H.H. Freeze: None. W. Gahl: None. M. Malicdan: None. J. Posey: None. J. Lupski: None. J. Baron: None. Genetic defects that impair growth plate chondrogenesis can result in a spectrum of phenotypes, ranging from skeletal dysplasia to mild short stature, sometimes accompanied by syndromic features. However, the genetic underpinnings of impaired skeletal growth often remain elusive. In our study, we investigated three unrelated families with short stature (height standard deviation score z < -2), distinctive facies (down-slanting eyes, low set ears, high arched palate, and short neck), and various neurodevelopmental abnormalities (from leaning difficulties to low intelligence quotient). In these families, exome sequencing (ES) identified rare, predicted-pathogenic variant alleles in WASHC3 that segregated with the phenotype. WASHC3 is a component of the WASH complex, which is involved in endosome receptor recycling. In the first family, a de novo-dominant missense variant (p.L69F) impaired WASHC3 participation in the WASH complex. This variant led to altered PTH1R endosomal trafficking, resulting in diminished PTH1R signaling and impairing growth plate chondrocyte hypertrophic differentiation, providing a likely explanation for the short stature. Knockdown of other WASH complex components (WASH1, SWIP, Strumpellin) also diminished PTH1R signaling, confirming the importance of an intact WASH complex. In the second and third families, a homozygous variant in the start codon (p.M1?) markedly reduced WASHC3 protein expression by approximately 75%. In conclusion, our findings strongly suggest that the WASH complex is required for normal skeletal growth and that, consequently, genetic abnormalities impairing the function of the WASH complex (WASHopathy) cause short stature as well as distinctive facies and variable neurodevelopmental abnormalities. These effects are likely mediated through disruptions in endosomal receptor trafficking. This new pathological information sheds light on the molecular basis of impaired longitudinal bone growth. Presentation: 6/3/2024