Abstract
Abstract: :
Purpose:X–Linked Retinoschisis (XLRS) is the most common cause for juvenile macular degeneration in males. XLRS a recessively inherited degenerative retinopathy is characterized by splitting in the nerve fibre layer. The XLRS gene has 6 exons encoding a 224 amino acid protein, which after N–terminal cleavage results in a 201 amino acid protein. The aim of this study was to screen affected Australian individuals for mutations in the XLRS gene. Methods:Leukocyte DNA extraction was performed on blood samples from 15 patients from 8 presumably unrelated families, known to have XLRS. All six exon fragments of the XLRS gene were amplified though polymerase chain reactions (PCR) using intronic primers1. Sequencing analysis was performed using an ABI Prism 310 Genetic AnalyzerTM and SequencherTM. To assess functional implications of potential missense mutations, comparison between the amino acid sequence within the discoid family of proteins as well as interspecies comparison of the XLRS protein was performed. Results:Four novel mutations were found. Of these there were two point mutations (1: 527T→C, Phe176Ser; 2: 305G→A, Arg102Gln), one codon deletion which resulted in loss of one amino acid (327–329del, Cys110del), and one point deletion (574Gdel) which caused a frameshift mutation resulting in the C–terminal containing a novel set of 42 amino acids, 11 amino acids longer than the normal protein (193Profs). Three previously identified point mutations were identified (1: 336G→C, Trp112Cys; 2: 418G→A, Gln140Arg; 3: 625C→T, Arg209Cys). Each mutation identified was found to alter an amino acid which was conserved across the fugu, mouse and human species. In two individuals from one family exon 2 was unable to be amplified indicating the likely presence of a significant deletion as previously described. All remaining exon sequences were normal. Conclusion:Population based genetic studies of XLRS have not previously been conducted in Australia. Identifying common mutations in the XLRS gene will hopefully lead to earlier and more accurate diagnosis. This study implicates the discoid domain as being of fundamental functional importance in the XLRS protein.
Keywords: retinal degenerations: hereditary • genetics