A novel deletion-insertion variant of <i>RS1</i> in X-linked retinoschisis

Structural variants such as large deletions or insertions are rarely observed in the <i>RS1</i> gene. Here, we report a 20-year-old male patient with X-linked retinoschisis (XLRS) carrying a novel deletion-insertion variant of <i>RS1</i>. In addition to ophthalmological examinations, molecular genetic analyses were performed using exome sequencing, polymerase chain reaction and Sanger sequencing. The patient was diagnosed with XLRS based on findings from funduscopy, optical coherence tomography, and full-field electroretinography. Exome sequencing identified a deletion of <i>RS1</i> exon 4, located between exons 19 and 20 of the <i>CDKL5</i> gene, which is oriented in the reverse direction relative to <i>RS1</i>. Ultimately, we confirmed a 453 bp deletion, including exon 4 of <i>RS1</i>, along with a 15 bp insertion at the deletion site, by verifying sufficient sequencing coverage for exons 19 and 20 of <i>CDKL5</i>. Exome sequencing is valuable not only for detecting single nucleotide variants but also for identifying exon deletions. Determining the coverage of exon regions in the <i>CDKL5</i> gene can assist in defining deletion-insertion variants in <i>RS1</i>.