OBJECTIVETo investigate the disease-causing mutation in a Chinese family affected with Usher syndrome type II.

METHODSAll of the 11 members from the family underwent comprehensive ophthalmologic examination and hearing test, and their genomic DNA were isolated from venous leukocytes. PCR and direct sequencing of USH2A gene were performed for the proband. Wild type and mutant type minigene vectors containing exon 42, intron 42 and exon 43 of the USH2A gene were constructed and transfected into Hela cells by lipofectamine reagent. Reverse transcription (RT)-PCR was carried out to verify the splicing of the minigenes.

RESULTSPedigree analysis and clinical diagnosis indicated that the patients have suffered from autosomal recessive Usher syndrome type II. DNA sequencing has detected a homozygous c.8559-2A>G mutation of the USH2A gene in the proband, which has co-segregated with the disease in the family. The mutation has affected a conserved splice site in intron 42, which has led to inactivation of the splice site. Minigene experiment has confirmed the retaining of intron 42 in mature mRNA.

CONCLUSIONThe c.8559-2A>G mutation in the USH2A gene probably underlies the Usher syndrome type II in this family. The splice site mutation has resulted in abnormal splicing of USH2A pre-mRNA.