NM_000330.4(RS1):c.175T>A (p.Cys59Ser) is a missense variant encoding the substitution of cysteine with serine at amino acid 59, 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). A missense variant encoding the same amino acid substitution, NM_000330.4(RS1):c.176G>C (p.Cys59Ser), (PMIDs: 12746437,19849666, 23288992, 35456481, 34645606) has been classified as pathogenic for X-linked retinoschisis by the ClinGen X-linked IRD VCEP, while no benign missense variants have been identified in this codon. SpliceAI has been used to confirm that neither variant has a predicted impact on RS1 splicing. The PS1 code was not considered to avoid circularity. This variant is absent from hemizygous individuals in gnomAD v4.1.0 (PM2_Supporting). This variant has been reported in at least 2 apparently unrelated probands meeting the PS4 requirement of a male diagnosed with XLRS (PMIDs: 10450864, 17987333, 9618178, 35982512, PS4_Supporting). Knock-in mice harboring the variant exhibited reduced electroretinogram b-wave amplitudes and developed schisis (PMID: 31174210, PS3). The computational predictor REVEL gives a score of 0.916, 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 is not met as this code is ineligible to be combined with the PM1_Strong code. The computational splicing predictor SpliceAI gives a delta score of 0.00 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. In summary, this variant is classified as 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, and PS4_Supporting.