NM_000330.4(RS1):c.544C>T (p.Arg182Cys) is a missense variant encoding the substitution of arginine with cysteine at amino acid 182. This variant is present in gnomAD v.4.1.0 at a frequency of 0.000002506 among hemizygous individuals, with 1 variant alleles / 399013 total hemizygous alleles, which is between the ClinGen X-linked IRD VCEP PM2_Supporting and BS1 threshold of 0.000002 to 0.00002 and fails to meet these criteria. The computational predictor REVEL gives a score of 0.917, 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). 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. COS7 cells exogenously expressing the variant exhibit reduced RS1 secretion into the medium relative to the wild-type control (PMID: 16361673, PMID: 29851975, PS3_Supporting). This variant has been reported in at least 9 apparently unrelated probands meeting the PS4 requirement of a male diagnosed with X-linked retinoschisis (PMID: 19568363, PMID: 34645606, PMID: 29851975, PMID: 34828422, PMID: 30652005, PMID: 34822951, PMID: 36377647, PMID: 39462066, PMID: 33546218, PS4_VeryStrong). 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: PP3_Moderate, PS3_Supporting, and PS4_VeryStrong.