The NM_000212.2(ITGB3):c.1199G>A (p.Cys400Tyr) missense has been identified in at least 4 probands, including GT11 and GT15a of PMID: 29675921 meeting the criteria for PP4_strong; including mucocutaneous bleeding, impaired aggregation with all agonists except ristocetin, and reduced surface expression of αIIbβ3 measured by flow cytometry. ITGA2B and ITGB3 were sequenced across all exons and intron/exon boundaries. Siblings GT15a and GT15b are both compound heterozygous for Cys400Tyr and pathogenic variant c.1525del (PP1; PMID: 29675921) with confirmation of trans phase was reported in PMID: 18788610. Additionally, two homozygous patients have been reported (PMIDs: 8781422, 35198519) (PM3_Strong). This variant is absent from gnomAD v4.1.0 (PM2_Supporting). The computational predictor REVEL gives a score of 0.968, which predicts a damaging effect on ITGB3 function (PP3). In summary, this variant meets the criteria to be classified as Pathogenic for autosomal recessive Glanzmann Thrombasthenia based on the ACMG/AMP criteria applied, as specified by the ClinGen PD VCEP: PM2_supporting, PM3_strong, PP1, PP3, PP4_strong. (VCEP specifications version 2; date of approval 06/06/2024)