Background Mutations in GJB2 gene are a major cause of autosomal recessive congenital hearing loss and the cause in some rare cases of the autosomal dominant form The purpose of this study was to investigate the frequency and the features of GJB2 mutations in the Chinese patients with congenital sensorineural deafness Methods Using PCR amplifying the entire coding region of GJB2 gene and direct DNA sequencing to analyze mutations in this gene among unrelated 69 cases with autosomal recessive congenital nonsyndromic deafness and 27 cases of dominant congenital deafness and 35 sporadic cases We also detected mutations in GJB2 in 100 control subjects with normal hearing Results 17 4% (12/69) of the probands in the autosomal recessive, 7 4% (2/27) of dominant families and 5 7% (2/35) of the sporadic congenital deafness patients had deafness causing mutations in GJB2, respectively Nine types of the mutations in GJB2 were detected in the recessive and sporadic group They consisted of five types of polymorphism, and four types of deafness causing mutation with homozygous 35delG in 1 sporadic (1/35), and 235delC frameshift mutation in 1 sporadic (homozygotes) and 10 recessive patients (2 heterozygotes and 8 homozygotes), and homozygous 442G→A missense mutation and homozygous 465T→A nonsense mutation in 1 different recessive proband, respectively The 465T→A that related to recessive deafness was a novel mutation found by this study The homozygous (10/69, 14 5%) and the heterozygous (2/69, 2 9%) GJB2 mutation in the recessive patients (12/69, 17 4%) and the homozygotes in the sporadic patient (2/35, 5 7%) all had congenital severe to profound sensorineural hearing loss 511G→A missense mutation and 299-300delAT frameshift mutation were found in two autosomal dominant congenital deafness families (2/27, 7 4%) The total mutation frequency of GJB2 was 12 2% (16/131) in the Chinese patients with congenital sensorineural deafness and 235delC was the most common deafness causing mutation Six types of mutation—5 types of polymorphism and 1 type of heterozygous deletion (235delC) mutation were found in the 100 control subjects The carry rate of the most frequent type of mutation 235delC was 0 5% in the controls(1/200 alleles) 109G→A was the most frequent (15/100, 15%) and 79G→A was the second common (8/100, 8%) polymorphism in this population Conclusions The general mutation rate of GJB2 is 12 2% (16/131) and the 235delC is the most common type of deafness causing mutation in Chinese patients with congenital hearing loss 465T→A nonsense mutation that is associated to autosomal recessive deafness is a novel mutation found by this screening 511G→A and 299-300delAT mutations contribute to autosomal dominant hearing loss The study further supports the view that the common types of mutation in GJB2 according to different ethnic Abstract:Background and that the mutation prevalence in the East Asian deafness population is lower than that in the white population Background Mutations in GJB2 gene are a major cause of autosomal recessive congenital hearing loss and the cause in some rare cases of the autosomal dominant form The purpose of this study was to investigate the frequency and the features of GJB2 mutations in the Chinese patients with congenital sensorineural deafness Methods Using PCR amplifying the entire coding region of GJB2 gene and direct DNA sequencing to analyze mutations in this gene in unrelated 69 cases with autosomal recessive congenital nonsyndromic deafness and 27 cases of dominant congenital deafness and 35 sporadic cases We also detected mutations in GJB2 in 100% control subjects with normal hearing Results 17% (12/69) of the probands in the autosomal recessive, 74% (2/27) of dominant families and 5% (2/35) of the sporadic congenital deafness patients had deafness causing mutations in GJB2, respectively Nine types of the mutations in GJB2 were detected in the recessive and sporadic group They consisted of five ty pes of polymorphism, and four types of deafness causing mutation with homozygous 35delG in 1 sporadic (1/35), and 235delC frameshift mutation in 1 sporadic (homozygotes) and 10 recessive patients (2 heterozygotes and 8 homozygotes), and homozygous 442G → A 465T → A that related to recessive deafness was a novel mutation found by this study The homozygous (10/69, 14 5%) and the heterozygous (2 / 69, 29%) GJB2 mutation in the recessive patients (12/69, 17 4%) and the homozygotes in the sporadic patient (2/35, 57%) all had congenital severe to profound sensorineural hearing loss 511G → A missense mutation and 299-300delAT frameshift mutation were found in two autosomal dominant congenital deafness families (2/27, 74%) The total mutation frequency of GJB2 was 12 2% (16/131) in the Chinese patients with congenital sensorineural deafness and 235delC was the most common deafness cau sing mutation Six types of mutation-5 types of polymorphism and 1 type of heterozygous deletion (235delC) mutation were found in the 100 control subjects The carry rate of the most frequent type of mutation 235delC was 0 5% in the controls (1/200 alleles ) 109G → A was the most frequent (15/100, 15%) and 79G → A was the second common (8/100, 8%) polymorphism in this population Conclusions The general mutation rate of GJB2 is 12 2% (16 / 131) and the 235delC is the most common type of deafness causing mutation in Chinese patients with congenital hearing loss 465T → A nonsense mutation that is associated to autosomal recessive deafness is a novel mutation found by this screening 511G → A and 299-300delAT. to autosomal dominant hearing loss The study further supports the view that the common types of mutation in GJB2 according to different ethnic Abstract: Background and that the the mutation prevalence in the East Asian deafness population is lower than that in the white population