# Altered chaperone–nonmuscle myosin II interactions drive pathogenicity of the UNC45A c.710T>C variant in osteo-oto-hepato-enteric syndrome

## TL;DR

This paper explains how a specific genetic mutation in the UNC45A gene causes a rare disease by disrupting normal cell functions, offering insights for potential treatments.

## Contribution

The study reveals a novel pathogenic mechanism of the UNC45A c.710T>C variant through altered chaperone–nonmuscle myosin II interactions.

## Key findings

- The UNC45A p.Leu237Pro mutant retains chaperone activity but forms stable oligomers that inhibit NMII functions.
- The variant causes impaired intracellular trafficking and abnormal transferrin retention in endocytic sites.
- Wild-type UNC45A coexpression reduces pathogenic effects by inhibiting excessive mutant oligomer formation.

## Abstract

The osteo-oto-hepato-enteric (O2HE) syndrome is a severe autosomal recessive disease ascribed to loss-of-function mutations in the Unc-45 myosin chaperone A (UNC45A) gene. The clinical spectrum includes bone fragility, hearing loss, cholestasis, and life-threatening diarrhea associated with microvillus inclusion disease–like enteropathy. Here, we present molecular and functional analysis of the UNC45A c.710T>C (p.Leu237Pro) missense variant, which revealed a unique pathogenicity compared with other genetic variants causing UNC45A deficiency. The UNC45A p.Leu237Pro mutant retained chaperone activity, prevented myosin aggregation, and supported proper nonmuscle myosin II (NMII) filament formation in patient fibroblasts and human osteosarcoma (U2OS) cells. However, the mutant formed atypically stable oligomers and prevented chaperone-myosin complex dissociation, thereby inhibiting NMII functions. Similar to biallelic UNC45A deficiency, this resulted in impaired intracellular trafficking, defective recycling, and abnormal retention of transferrin at various endocytic sites. In particular, coexpression of wild-type protein attenuated the pathogenic effects of the variant by inhibiting excessive oligomer formation. Our results elucidate the pathogenic mechanisms and recessive characteristics of this variant and may aid in the development of targeted therapies.

The manuscript provides a thorough molecular and functional analysis of the pathogenic non-muscle myosin co-chaperone UNC45A c.710T>C missense variant associated with early-onset Osteo-Oto-Hepato-Enteric (O2HE) Syndrome.