Research Of Hereditary Etiology Of A Family With Waardenburg Syndrome Type Ⅰ

Objective Waardenburg syndrome(WS),an autosomal dominant hereditary syndromic hearing impairment,is characterized by sensorineural deafness and abnormal pigmentation.In addition,WS type Ⅰ can also be accompanied by dystopia canthorum,the typical phenotype of WS Ⅰ,and other features such as broad nasal root and synophrys.In this study,we aim to investigate the hereditary etiology of a highly suspected WS family collected before,and to provide genetic counseling for this family so as to reduce the risk of raising deaf offspring.Methods Detailed history collection and systematic clinical examinations were performed for each member of the family to identify phenotypes,then draw the pedigree diagram.DNA was extracted from venous blood which was collected from the consenting family members.Three common deafness genes(GJB2,SLC26A4,MT-RNR1)and WS candidate genes(PAX3,MITF,SNAI2,EDNRB,EDN3,SOX10)were amplified by using nested polymerase chain reaction(PCR)technique,and the products were subjected to Sanger sequencing.The software Sequencher was applied to analysis the results.Sanger sequencing verified whether the suspicious mutation showed genotype-phenotype co-segregation within the family.Biological software tools were utilized to predict the pathogenicity of the suspected mutation and to analyze the conservation of the sequence where the mutation was located.The mutation was screened in 400 Han Chinese who own the normal audition.In order to reduce the risk of giving birth to deaf children,genetic counseling were provided for this family according to Mendelian inheritance rule.Results(1)Phenotypes: The proband Ⅲ-2 has the phenotypes of complete deafness in both ears,abnormal iris pigmentation(bilateral blue iris),dystopia canthorum(index W = 2.32),synophrys,broad nasal root and hypoplasia of alae nasi.His father has the phenotypes of mild sensorineural deafness on the left side,dystopia canthorum(index W = 2.46),early gray hair,synophrys,broad nasal root,hypoplasia of alae nasi,and mild constipation.Grandfather I-1 has dystopia canthorum(index W = 2.39)and premature graying of the hair.No abnormal phenotypes were found in other family members,including grandmother(Ⅰ-2),mother(Ⅱ-2),and proband’s elder sister(Ⅲ-1).(2)Genotype: No suspicious mutation was detected in the screening of three common deaf genes.However,a heterozygous variation of exon 2 of PAX3,c.109＿110ins GA(p.V38Afs*73),was detected in the screening of WS candidate gene,and showed genotypic-phenotypic co-separation within family members.(3)The results of conservation analysis of the mutation showed that the amino acid sequence from p.V38 to p.T110 of PAX3 protein was highly conserved.The results of pathogenicity prediction by biological software indicated that the mutation tended to be pathogenic.(4)The mutation was not detected in 400 normal hearing Han Chinese.Conclusion In this study,c.109＿110ins GA(p.V38Afs*73),a novel frameshift mutation,was found in exon 2 of PAX3 gene,which expands the variation spectrum of PAX3 gene.This newly discovered heterozygous mutation may be the pathogenic mutation of WS Ⅰ and the hereditary cause of the study family,and haploinsufficient may be the underlying pathogenic mechanism.The novel mutation discovered in this study enriches the genotype spectrum of WS.Genetic counseling was provided for this family according to the autosomal dominant inheritance mode of WS,thus reducing the risk of suffering from WS in offspring.