Targeted exon sequencing in Usher syndrome type I.

Area of Science:

• Genetics
• Ophthalmology
• Audiology

Background:

• Usher syndrome type I (USH1) is a genetic disorder characterized by retinitis pigmentosa, profound congenital hearing loss, and vestibular ataxia.
• At least six genes are currently associated with USH1, involving over 180 exons.
• Molecular diagnosis is crucial for understanding the genetic basis of USH1.

Purpose of the Study:

• To perform molecular diagnosis on a cohort of 47 USH1 probands using advanced techniques.
• To identify causative mutations and genetic variants in patients with USH1.
• To describe the clinical presentation of the studied USH1 cohort.

Main Methods:

• Selective exon capture and next-generation sequencing of known inherited retinal degeneration genes.
• Comparative genomic hybridization.
• Sanger sequencing of newly identified USH1 exons from retinal transcriptome analysis.

Main Results:

• Genetic diagnosis was achieved in 14 out of 47 probands by confirming biallelic mutations.
• Likely pathogenic variants were detected in 19 additional patients, pending cosegregation analysis.
• Twenty-one novel mutations were identified among the 33 genetically solved or likely solved patients.
• Ten patients carried additional rare USH1 alleles or variants in other deaf-blindness-associated genes, potentially influencing phenotype.

Conclusions:

• The study highlights significant genetic heterogeneity in the USH1 cohort, with numerous novel mutations.
• No clear genotype-phenotype correlation was observed, likely due to limited sample size for specific genotypes.