Whole Genome-wide Scanning For A Large Pedigree With Hereditary Hearing Impairment

Introduce and Objectives: Hearing impairment is a commonsensory disorder in the human population. The incidence of congenitalhearing impairment is estimated at 1 in 1000 births, of whichapproximately equal numbers of cases are attributed to environmentaland genetic factors. Of the hearing-impairment disorders attributableto genetic causes, 70% are classified as nonsyndromic and theremaining 30% as syndromic. Among the many disorders classified assyndromic hearing impairment, the pathology varies widely, but, innonsyndromic deafness, the defect is generally sensorineural.Nonsyndromic hearing impairment can be further subdivided by modeof inheritance: 70% of cases are autosomal recessive, 22% areautosomal dominant, 1% are X-linked, and<1% are duo tomitochondrial inheritance. Dominant loci are denoted with the prefix"DFNA'', recessive loci with "DFNB'', X-linked loci with "DFN'',and modifying loci with "DFNM''. Generally, patients with autosomalrecessive hearing impairment have prelingual and profound deafness,and patients with autosomal dominant hearing impairment haveprogresswive and postlingual hearing impairment. This observationmay be explained by the complete absence of functional protein inpatients with recessive disorders, dominant mutations may beconsistent with initial function and subsequent hearing impairment dueto accumulation of pathology. over the past 5 years, remarkableprogress has been made in the identification of new loci fornonsyndromic hearing impairment (NSHL) and in the cloning ofdeafness genes. To date, 77 loci have been reported for nonsyndromicdeafness: 40 autosomal dominant, 30 autosomal recessive, and 7X-linked. In addition, 51 auditory genes have been identified: 15 forautosomal dominant NSHI loci, 9 for autosomal recessive NSHL loci,2 for X-linked NSHL loci, 5 mitochondrial, and>=32 genes forsyndromic hearing impairment (some genes cause multiple forms ofdeafness). Although significant advances have been made, there is nodoubt that many more genes await discovery. Identifying these genesand characterizing the proteins they encode will increase ourknowledge of the molecular processes involved in the auditory systemand will improve our understanding of how such processes canbecome altered and lead to hearing impairment. Now we collect adeafness pedigree that have less characters of hereditary conductivehearing impairment, so we apply clinic and biologic methods to searchrelated gene for gene diagnosis and therapy. Study Design and methods: All subjects in the pedigree wasinterviewed personally and their clinical data and genetic backgrounddata are collected; Audiological Examination (pure-tone audiometry,Acoustic Immittance measurement), Supplementary Examination(High-resolution CT, Immunologic tests, Chromatosome Caryotype)and Surgery are applied. Peripheral blood samples were obtained fromavailable family members for isolating genomic DNA. we selected 1candidate gene (POU3F4) playing important roles in X-linkedhereditary conductive hearing impairment from genomic databases inhttp://www.hereditary hearing loss.org/. we use PCR-SSCP methods todetect POU3F4 gene in order to certify that it is not related to deafnessof this pedigree. Finally two-point linkage analysis was conductedusing the MLINK and ILINK programs from the Linkage version5.1software. Results: Pedigree Analysis: Pedigree analysis indicated thatpatients distributed four continuous generations and each one nomatter they were male or female had 50% chance of recieving theautosome bearing the mutant gene and being affected. And theprevalence rate of female patients was larger than it of male patients.Furthermore, only female patients can transmit the mutant gene to herlater generations, males'were not observed this phenomenon.Although it maybe shows an autosome dominant inheritance, wesuspect that it is mostly an X-linked dominant inheritance.Audiological Examination Data: 1.pure-tone audiometry: Audiogramin the 9 hearing-impaired patients identified in the present study,pure-tone audiograms showed conductive deafness. 2.AcousticImmittance measurement: Acoustic Immittance measurement in the 7patients showed all of them are both ears'A form curve, and indicatedthat the pressure of tympanic cavity was normal. This examinationexcludes hearing loss caused by secretory otitis media or suppurativeotitis media. Supplementary Examination 1. High-resolution CT:High-resolution CT scan of temporal bonein two patients showed normal inner structures including the vestibularaqueduct ,semicircular canals and internal auditory canal. 2.Immunologic tests: All of the immunologic tests to the members ofthis pedigree including RHF, CRP, ASO, HLA-27 and antinuclearantibody examinations were negtive. 3. Chromatosome Caryotype: â…¢2 was accepted chromatosome caryotype analysis. The chromatosomeshowed 46, XX. Surgery: In the patients described here, tympanotomyshowed her stapes was flat cylinder shape, stape footplate fix onfossulae fenestrae vestabuli and parallel to the stapedial tendon,respectively, which excludes otosclerosis. After this operation, theprobands'left ear hearing achieved normal level one month later.Tinnitus and vertigo appearing after operation were disappeared twoweeks later. candidate gene detection: It does not detect mutation ofPOU3F4 gene in this Pedigree. None of the patients was affected byPOU3F4 gene. genome scan: Two-point LOD scores of the dxs1060microsatellite marker and disease gene is 2.044489 at recombinationfraction 0.00. The loci dxs1060 microsatellite marker is on x-chromosome (Xp22). CONCLUSION:In this study, we have confirmed this family as...