The Molecular Genetics Research Of Retinitis Pigmentosa/Usher Syndrom Pedigree

Purpose To identify the disease-causing gene in a four-generation Chinese family affected with retinitis pigmentosa(RP). On this basis, gene diagnosis and genetic consult were perfomed for the family members.Methods 1)All patients in the family underwent careful ophthalmologic examination, including visual acuity, slit-lamp, fundus ophthalmoscopy, visual field test, and electroretinogram (ERG). Initial RP diagnosis was based on the description of night blindness, typical RP fundus appearance, non-detectable electroretinogram and loss of peripheral visual fields.2) Whole peripheral blood was collected from all participants, and genomic DNA was isolated using the DNA isolation kit for Mammalian Blood.3) A panel of candidate genetic loci for retinitis pigmentosa, including 38 known RP genes, was selected for preliminary linkage and haplotype analysis.4) When the disease gene was mapped to chromosome 1q41 where USH2A harbors, patients were given audiometric and vestibular tests. Audiometric tests included otoscopy and standard pure-tone audiometry. Vestibular function was evaluated by caloric test, rotatory chair and electronystagmography. The final clinical diagnosis of USH2 was verified based on typical RP symptoms companied with sensorineural hearing impairment and normal vestibular function.5) The complete coding region and exon-intron boundaries of Usher syndrome2A (USH2A) were sequenced with the proband DNA to screen the disease-causing gene mutation.6) Restriction fragment length polymorphism (RFLP) analysis and direct DNA sequence analysis were done to demonstrate co-segregation of the USH2A mutations with the family disease. One hundred normal controls were used without the mutations.Results 1) The disease-causing gene in this Chinese family was linked to the USH2A locus on chromosome 1q41.2) Direct DNA sequence analysis of USH2A identified two novel mutations in the patients:one missense mutation p.G1734R in exon 26 and a splice site mutation, IVS32+1G>A, which was found in the donor site of intron 32 of USH2A.3) Subsequent RFLP analysis and direct DNA sequence analysis displayed that the p.G1734R and IVS32+1G>A mutation were not found in the unaffected family members or the 100 normal controls.4) One patient with a homozygous mutation displayed only RP symptoms until now, while three patients with compound heterozygous mutations in the family of study showed both RP and hearing impairment. Conclusions This study identified two novel mutations:p.G1734R and IVS32+1G>A of USH2A in a four-generation Chinese RP family. In this study, the heterozygous mutation and the homozygous mutation in USH2A may cause Usher syndrome Typeâ…¡or RP, respectively. These findings expand the spectrum of mutations in longer isoform of USH2A and provide useful information for genetic counseling for patients and families with USH2.