Abstract
Purpose :
The aim of this study is to characterize the clinical features and genetic defects of five unrelated Chinese patients with usher syndrome. In addition, to investigate the pathogenesis of USH2A, we generated a USH2A knockout mouse line and performed preliminary characterization.
Methods :
Complete ophthalmic examinations, including slit-lamp biomicroscopy, dilated fundus examination, spectral domain optical coherence tomography and full-field electroretinography were performed. Genomic DNA was prepared and a screening of pathogenic genes associated with retinal diseases or deafness was performed using targeted sequence capture array technique. Polymerase chain reaction and direct sequencing were used to confirm the results. Crispr/cas9 technology was used to construct ush2a knockout mouse line.
Results :
Five patients with Usher syndrome from five unrelated Chinese families were recruited in this study, including a 4-year-old girl, a 21-year-old girl, a 22-year-old girl, a 24-year-old boy and a 29-year-old man. All patients showed night blindness and hearing loss but without vertigo. One patient have a small patchy of retinal pigmentation, but others have not obvious pigmentation. Five different heterozygous compound mutations were found, including MYO7A (c.1003+1G>A, c.5957_5958del; c.1679 A>G, c.2680 G>T) and USH2A (c.3996C>A, c.2187C>A, c.997T>C; c.8559-2A>G, exon28-33 del; c.2187C>A, c.997T>C, c.538T>C). The electroretinogram (ERG) showed markedly decreased cone and rod responses in both eyes. The amplitudes of the a- and b-waves were significantly reduced in the photopic (which reflects cone response), scotopic (which reflects rod response) and the maximal scotopic ERG (which reflects cone and rod response) in all patients. Optical coherence tomography showed highly reflective lesions extending from RPE to the level of the outer segments. Ush2a knockout mice didn't showed dramatically reduced amplitudes of a- and b-waves of ERG, but hearing loss was found at 3 months.
Conclusions :
We expand the spectrum of USH2A/MYO7A mutations causing Usher syndrome and our study also emphasized the importance of molecular genetic analysis in confirming clinical diagnosis and clinical subtypes. We generated a Ush2a knockout mouse line, which mimick Usher syndrome type 2 in humans. We will further characterize detailed phenotype and deepen our understanding of USH2a in retinal degeneration.
This is a 2020 ARVO Annual Meeting abstract.