NM_000330.4(RS1):c.329G>A (p.Cys110Tyr) is a missense encoding the substitution of cysteine with tyrosine at amino acid 110, which is a critical amino acid residue involved in disulfide bridge formation as defined by the ClinGen X-linked IRD VCEP (PMID: 26812435, PM1_Strong). This variant is absent from hemizygous individuals in gnomAD v4.1.0 (PM2_Supporting). This variant has been reported in at least 6 apparently unrelated probands meeting the PS4 requirement of a male diagnosed with X-linked retinoschisis (PMID: 9618178, PMID: 28348004, PMID: 34822951, PMID: 38219857, PMID: 30551202, PMID: 31456290, PMID: 35456422, PMID: 34645606, PS4). The variant has been reported to segregate with X-linked retinoschisis through two affected brothers from a single family (PP1; PMID: 32856788, PMID: 35456422). The computational predictor REVEL gives a score of 0.882, which is within the ClinGen X-linked IRD VCEP range between 0.931 to 0.773 and predicts a damaging effect on RS1 function. PP3_Moderate is not met as the code is ineligible to be used in combination with PM1_Strong. The computational splicing predictor SpliceAI gives a delta score of <0.02 for all predictive splice changes, which is below the ClinGen X-linked IRD VCEP threshold of >0.2 and does not predict that the variant disrupts RS1 splicing. HEK293 cells exogenously expressing the variant exhibit loss of RS1 secretion into the medium relative to the wild-type control due to intracellular retention and failure of the variant protein to properly assemble into multimers (PMID: 19849666, PS3_Supporting). In summary, this variant is classified as likely pathogenic for X-linked retinoschisis based on the ClinGen X-linked Inherited Retinal Disease Expert Panel Specifications to the ACMG/AMP Variant Interpretation Guidelines for RS1 Version 1.0.0: PM2_Supporting, PM1_Strong, PS3_Supporting, PS4, and PP1.