[Mutational frequencies in usherin(USH2A gene) in 26 Colombian individuals with Usher syndrome type II].

INTRODUCTION

Usher syndrome is a disorder characterized by progressive retinitis pigmentosa, prelingual sensory hearing loss and vestibular dysfunction. It is the most frequent cause of deaf-blindness in humans. Three clinical types and twelve genetic subtypes have been characterized. Type II is the most common, and among these cases, nearly 80% have mutations in the USH2A gene.

OBJECTIVE

The aim of the study was to establish the mutational frequencies for the short isoform of USH2A gene in Usher syndrome type II.

MATERIALS AND METHODS

Twenty-six Colombian individuals with Usher syndrome type II were included. SSCP analysis for 20 exons of the short isoform was performed and abnormal patterns were sequenced. Sequencing of exon 13 of the USH2A gene was performed for all the individuals because the most frequent mutation is located in this exon.

RESULTS

The most frequent mutation was c.2299delG, identified in the 27% (n=8) of the sample. The second mutation, p.R334W, showed a frequency of 15%. A new variant identified in the 5’UTR region, g.129G>T, was present in 1 individual (4%). Four polymorphisms were identified; one of them is a new deletion in exon 20, first reported in this study.

CONCLUSIONS

Mutations in the usherin short isoform were identified in 38% of a sample of 26 USH2 cases. Molecular diagnosis was established in 7 of the 26.