NM_000330.4(RS1):c.422G>C (p.Arg141Pro) is a missense variant encoding the substitution of arginine with proline at amino acid 141. Another missense variant in the same codon, NM_000330.4(RS1):c.422G>A (p.Arg141His), (PMID: 29851975, PMID: 34645606, PMID: 30450322, PMID: 29739629, PMID: 35984651, PMID: 30652005, PMID: 19093009, PMID: 30630865, PMID: 30040949, PMID: 17525175, PMID: 30630865, PMID: 30040949) 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. The present variant has a higher Grantham’s distance (103) than the comparison variant (29), and SpliceAI has been used to confirm that neither variant has a predicted impact on RS1 splicing (PM5). This variant is absent from hemizygous individuals in gnomAD v4.1.0 (PM2_Supporting). At least one proband harboring this variant exhibits phenotypes including appearance of schisis and reduced visual acuity before age 13 years, which together are specific for X-linked retinoschisis (PMID: 33460243, PP4). The computational predictor REVEL gives a score of 0.955, which is above the ClinGen X-linked IRD VCEP threshold of >0.932 and predicts a damaging effect on RS1 function (PP3_Strong). The computational splicing predictor SpliceAI gives a delta score of 0.02 for acceptor loss, 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 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, PP3_Strong, PM5, and PP4.