Resumen de Usher syndrome: molecular analysis of the ush2 genes and development of a next-generation sequencing platform
Usher syndrome is a genetic disorder combining sensorineural hearing loss (HL) and retinitis pigmentosa (RP). Some patients will also exhibit vestibular areflexia (VA). Clinical and genetic heterogeneity is recognized as the 3 clinical subgroups, defined mainly on the degree of HL and VA, can be caused by mutations in one of the 10 known genes. It is important to use all accessible genetic tools to identify and characterize molecular origin in order to improve the knowledge of the physiopathological mechanisms causing Usher Syndrome.
In this context, we have performed an exhaustive molecular analysis of the three causative USH2 genes (USH2A, GPR98 and DFNB31). The study was not limited to the search of point mutations; CGH-array analysis, computational predictions and functional studies were carried out when necessary. Thanks to this work, we determined that in Spain, USH2A and GPR98 are responsible for 94.8% and 5.2% of USH2 mutated cases, respectively. DFNB31 plays a minor role in the Spanish population. USH3 is thought to be a minor type of USH in our population.
Mutations in CLRN1 were initially responsible for USH3, but mutations in this gene have also been reported in patients with clinical features similar to USH1 or USH2. In this work, we have reported the results of the molecular analysis of CLRN1 in a cohort of patients and the low involvement of this gene in our population.
We have then designed a targeted exome of the Usher genes to be sequenced using the GS Junior system (Roche 454). The aim of the study was to test the feasibility of this new technics for a possible transfer to diagnostic facilities. Quality criteria and variant prioritization were set up on a control cohort (previously studied in one of the USH gene). The study has then been extended on a patient cohort. Our results indicate that NGS Usher-exome can be used in molecular diagnostics but improvement of the reliability of the sequencing technology, bioinformatics tools and dedicated databases is essential.
