title: Next-generation sequencing identifies mutations of SMPX, which encodes the small muscle protein, X-linked, as a cause of progressive hearing impairment.
abstract: In a Dutch family with an X-linked postlingual progressive hearing impairment, a critical linkage interval was determined to span a region of 12.9 Mb flanked by the markers DXS7108 and DXS7110. This interval overlaps with the previously described DFNX4 locus and contains 75 annotated genes. Subsequent next-generation sequencing (NGS) detected one variant within the linkage interval, a nonsense mutation in SMPX. SMPX encodes the small muscle protein, X-linked (SMPX). Further screening was performed on 26 index patients from small families for which X-linked inheritance of nonsyndromic hearing impairment (NSHI) was not excluded. We detected a frameshift mutation in SMPX in one of the patients. Segregation analysis of both mutations in the families in whom they were found revealed that the mutations cosegregated with hearing impairment. Although we show that SMPX is expressed in many different organs, including the human inner ear, no obvious symptoms other than hearing impairment were observed in the patients. SMPX had previously been demonstrated to be specifically expressed in striated muscle and, therefore, seemed an unlikely candidate gene for hearing impairment. We hypothesize that SMPX functions in inner ear development and/or maintenance in the IGF-1 pathway, the integrin pathway through Rac1, or both.
authors.affiliation: Department of Otorhinolaryngology, Head and Neck Surgery, Nijmegen, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: Margit
authors.initials: M
authors.lastname: Schraders
authors.forename: Stefan A
authors.initials: SA
authors.lastname: Haas
authors.forename: Nicole J D
authors.initials: NJ
authors.lastname: Weegerink
authors.forename: Jaap
authors.initials: J
authors.lastname: Oostrik
authors.forename: Hao
authors.initials: H
authors.lastname: Hu
authors.forename: Lies H
authors.initials: LH
authors.lastname: Hoefsloot
authors.forename: Sriram
authors.initials: S
authors.lastname: Kannan
authors.forename: Patrick L M
authors.initials: PL
authors.lastname: Huygen
authors.forename: Ronald J E
authors.initials: RJ
authors.lastname: Pennings
authors.forename: Ronald J C
authors.initials: RJ
authors.lastname: Admiraal
authors.forename: Vera M
authors.initials: VM
authors.lastname: Kalscheuer
authors.forename: Henricus P M
authors.initials: HP
authors.lastname: Kunst
authors.forename: Hannie
authors.initials: H
authors.lastname: Kremer
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D018389:Codon, Nonsense; D004252:DNA Mutational Analysis; D005260:Female; D016368:Frameshift Mutation; D050172:Genes, X-Linked; D034381:Hearing Loss / Q000235:genetics* / Q000473:pathology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics; D008297:Male; D008875:Middle Aged; D058977:Molecular Sequence Annotation; D009124:Muscle Proteins / Q000235:genetics*; D010375:Pedigree; D020641:Polymorphism, Single Nucleotide; D017421:Sequence Analysis; D055815:Young Adult
chemical_list: D018389:Codon, Nonsense; D009124:Muscle Proteins; C433890:SMPX protein, human; D007334:Insulin-Like Growth Factor I