A novel frameshift mutation of SMPX causes a rare form of X-linked nonsyndromic hearing loss in a Chinese family

X-linked hearing impairment is the rarest form of genetic hearing loss (HL) and represents only a minor fraction of all cases. The aim of this study was to investigate the cause of X-linked inherited sensorineural HL in a four-generation Chinese family. A novel duplication variant (c.217dupA, p.Ile73Asnfs*5) in SMPX was identified by whole-exome sequencing. The frameshift mutation predicted to result in the premature truncation of the SMPX protein was co-segregated with the HL phenotype and was absent in 295 normal controls. Subpopulation screening of the coding exons and flanking introns of SMPX was further performed for 338 Chinese patients with nonsydromic HL by Sanger sequencing, and another two potential causative substitutions (c.238C>A and c.55A>G) in SMPX were identified in additional sporadic cases of congenital deafness. Collectively, this study is the first to report the role of SMPX in Chinese population and identify a novel frameshift mutation in SMPX that causes not only nonsyndromic late-onset progressive HL, but also congenital hearing impairment. Our findings extend the mutation and phenotypic spectrum of the SMPX gene.