Proteasome subunit PSMC3 variants cause neurosensory syndrome combining deafness and cataract due to proteotoxic stress

Whole-genome sequencing was performed on patients with severe deafness and early-onset cataracts as part of a neurological, sensorial and cutaneous novel syndrome. A unique deep intronic homozygous variant in the PSMC3 gene (c.1127+337A>G, p.Ser376Argfs15*), encoding the 26S proteasome ATPase ring subunit 5 (Rpt5) was identified leading to the transcription of a cryptic exon. Patient’s fibroblasts exhibited impaired protein homeostasis characterized by accumulation of ubiquitinated proteins suggesting severe proteotoxic stress. Indeed, the TCF11/Nrf1 transcriptional pathway allowing proteasome recovery after proteasome inhibition is permanently activated in the patient’s fibroblasts. Upon chemical proteasome inhibition this pathway is however impaired. These cells were unable to compensate for proteotoxic stress although a higher proteasome content. Two different zebrafish studies led to inner ear development anomalies as well as cataracts. PSMC3 proteasome subunit dysfunction leads to various neurological manifestations, early onset cataracts and deafness and suggest that Rpt5 plays a major role in inner ear, lens and central nervous system development.