Mapping And Identified The Causative Genes In Chinese Nonsyndromic X-linked Hereditary Hearing Loss Pedigrees

Hearing loss is the most common sensory disorder,one in every 1,000 newborn suffers from congenital hearing impairment.More than 60%of the congenital cases are caused by genetic factors.Non-syndromic forms are responsible for 70%of the cases of hereditary etiology and syndromic cases represent 30%of them.Among the forms of heritage,autonomic recessive is the most frequent one(75%-85%),followed by dominant heritage(12-13%),X-linked and Y-linked or mitochondrial,with 2-3%of the cases of non-syndromic hearing loss.Molecular genetics of deafness has experienced remarkable progress in the last decade.Genes responsible for hereditary hearing impairment are being mapped and cloned progressively.Our reach focuses on non-syndromic X-linked hereditary hearing impairment.PartⅠ:Linkage analysis of an nonsyndromic X-linked hereditary deafness pedigree(GZ-2001)and identified the causative mutation in PRPS1 gene.We paid our attention to a large X-linked deafness pedigree collected from guizhou province of southern china(GZ-Z001family).There are totally five generations 106 members in the family with character of non-syndromic X-linked dominant hearing loss.Preliminary X-chromosome mapping in GZ-Z001family was performed using the ABI Prism set version 2,panel 28,obtained from Applied Biosystems.The family was genotyped for a set of microsatellite markers evenly spaced at intervals of about 10 cM.we found the maximum lod score of 2.45 at theta=0.0 for DXS1106.markers for the fine mapping of the candidate regions were spaced at about 0.4-1cM from Meshfield website,the forward primers for these microsatellites were labeled with different fluorescents,and got the max lod score of 4.25 at theta=0.0 for DXS8096.The position of the deafness locus was refined by haplotype analysis,flanking recombinations were observed at DXS8020 and DXS1059,and to define the interval 5.41cM of the locus.We have direct sequenced 14 candidate genes in the family including 12 genes in the region,and identified a 193G＞A transversion in exon 2 of the PRPS1 gene in all male affected patients,resulting in a asp65-to-asn(D65N)substitution,the female carriers showed heterozygosis.Again,we confirmed that D65N was not observed in 80 unrelated control chromosomes outside the pedigree.The mutated amino acids showed perfect conservation from canis to human.Part 2:mapping a disease locus for the second nonsyndromic X-linked genetic hearing impairment family(JX-L005).we investigated a family from jiangxi province of china(JX-L005family). There are 5 male patients with profound deafness and 1 female member with moderate hearing loss in the pedigree.Materials and method paralleled with the first part.At last we found the max lod score at marker DXS1227=2.04 (theta=0.0).recombinations were found frequency around the marker and to define the interval 4.08 c M between DXS1205 and DXS8106.Directed sequencing analyses of the TIMM8A gene and POU3F4 gene had not identified mutations.ConclusionIn part one,we mapping a locus for the nonsyndromic X-linked hereditary deafness pedigree(GZ-Z001)and found that the deafness was associated with a 193G＞C transversion in exon 2 of the PRPS1 gene that resulted in a asp65asn substitution.In part two,we found a locus on X chromosome of the nonsyndromic X-linked genetic hearing impairment family(JX-L005).