The NM_000330.4(RS1):c.214G>A variant is a missense variant encoding the substitution of Glutamic acid with Lysine at amino acid 72. This variant is present in gnomAD v.4.1.0 at a frequency of 0.000002508 among hemizygous individuals, with 1 variant alleles / 398646 total hemizygous alleles, which is between the ClinGen X-linked IRD VCEP PM2_Supporting and BS1 thresholds of <0.000002 and >0.00002 and fails to meet these criteria. The computational predictor REVEL gives a score of 0.921, 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. HEK293 cells exogenously expressing the variant exhibit loss of RS1 secretion into the medium relative to the wild-type control (PMID: 12746437, PS3_Supporting). This variant p.Glu72Lys, of the RS1 gene, is an established residue involved in cross-linking the adjacent RS1 subunit by the ClinGen X-linked IRD VCEP (PMID: 27114531, PM1). The variant has been reported to segregate with retinal dystrophy through at least 3 meioses in the same family (PP1_Strong; PMID: 11246454, 38317323, 19324861). At least one proband harboring this variant exhibits a phenotype including appearance of schisis and reduced visual acuity before age 13 years, which together are specific for X-linked retinoschisis (PMID: 23288992, PP4). This variant has been reported in at least 6 apparently unrelated probands meeting one of the PS4 requirements of a male diagnosed with X-linked retinoschisis (PMIDs: 30025115, 28348004, 19324861, 22245991, 32531858, 29851975, PS4). 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, PP1_strong, PP4, PS4, PS3_supporting, and PM1 (date of approval 01/24/2025).