Nonsense mutations in the PAX3 gene cause Waardenburg syndrome type I in two Chinese patients

Background Waardenburg syndrome type I （WS1） is an autosomal dominant disorder characterized by sensorineural hearing loss, pigmental abnormalities of the eye, hair and skin, and dystopia canthorum. The gene mainly responsible for WS1 is PAX3 which is involved in melanocytic development and survival. Mutations of PAX3 have been reported in familiar or sporadic patients with WS1 in several populations of the world except Chinese. In order to explore the genetic background of Chinese WS1 patients, a mutation screening of PAX3 gene was carried out in four WS1 pedigrees. Methods A questionnaire survey and comprehensive clinical examination were conducted in four Chinese pedigrees of WSI. Genomic DNA from each patient and their family members was extracted and exons of PAX3 were amplified by PCR. PCR fragments were ethanol-purified and sequenced in both directions on an ABl_Prism 3100 DNA sequencer with the BigDye Terminator Cycle Sequencing Ready Reaction Kit. The sequences were obtained and aligned to the wild type sequence of PAX3 with the GeneTool program. Results Two nonsense PAX3 mutations have been found in the study population. One is heterozygous for a novel nonsense mutation S209X. The other is heterozygous for a previously reported mutation in European population R223X. Both mutations create stop codons leading to truncation of the PAX3 protein. Conclusions This is the first demonstration of PAX3 mutations in Chinese WS1 patients and one of the few examples of an identical mutation of PAX3 occurred in different populations.

Phenotype and genotype analysis of a Chinese family with prelingual X-linked hereditary hearing impairment

Background X-linked hearing impairment is clinically and genetically a heterogeneous disease. Although many disorders manifest with hearing loss, a limited number of sex-linked loci and only one gene （POU3F4） have been shown to be implicated in X-linked non-syndromic hearing impairment. In the present study, we have performed a clinical and genetic analysis of a Chinese family with X-linked non-syndromic hearing loss, with emphasis on audiological findings and genomic mapping. Methods The clinical features of Family JX01 were evaluated by physical and audiometric examination in eighteen family members. Mutation screening of POU3F4 was identified by polymerase chain reaction （PCR） amplification and sequencing. Molecular evaluation consisted of X-chromosome wide genotyping by microsatellite makers （STR）, followed by analyzing using MLINK computer program. Results Five affected males demonstrated bilateral, symmetrical sensorineural and profound hearing loss. The hearing impairment started prelingual. The female carriers did not have any complain of hearing loss, however, two of them were tested with milder loss with high frequency. No causative mutations in POU3F4 gene were detected by DNA sequencing. Linkage analysis indicated that the responsible gene was linked to locus DXS1227 （maximum Iod score=2.04 at θ=0）. Conclusions The affected males in Family JX01 have profound prelingual sensorineural hearing impairment. In addition, two female carriers showed mild to moderate hearing losses. However, none of females complained of any hearing loss. Analysis of hereditary deafness in this family mapped most compatibly to the Xq27.2.