Gene Duplication in a Patient With Usher Syndrome Type 2C: A Case Report

Variants of the <i>ADGRV1</i> gene cause Usher syndrome type 2C (USH2C). There are three types of Usher syndrome, all inherited in an autosomal recessive pattern. USH2C classically causes sensorineural hearing loss and progressive retinitis pigmentosa (RP) occurring in adolescence or adulthood. In this study, we report the case of a 34-year-old male with congenital sensorineural and progressive hearing loss and peripheral vision loss with a fundus examination of pale optic nerve with a cup-to-disk ratio of 0.40, arteriolar attenuation, arteriovenous ratio 2/5 with choroid-retinal degeneration, peripheral bony spicules, and fundus tessellation. Visual field test (30-2 Carl Zeiss Meditec, Inc.) showed that the patient had a mean deviation of -21.22 dB (p < 0.5) and 7.51 dB (p < 0.5) in the right and left eye, respectively. Upon full-field electroretinogram (ERG), the patient had non-recordable photopic and scotopic ERG responses bilaterally. The patient's macular optical coherence tomography showed an average thickness of 221 µm and a total macular volume of 8 mm³ in the right eye, and an average thickness of 215 µm and a total macular volume of 7.8 mm³in the left eye. Based on these ocular findings, the patient was clinically diagnosed with RP. Genetic testing with exome sequencing showed a homozygous pathogenic copy number variation (4) at exons 79-84 of the <i>ADGRV1</i> gene. Our case highlights the importance of recognizing the specific type of variant affecting a gene in hereditary diseases such as RP, as disease severity may be influenced by the nature of the variant.