The ITGB3 missense variant NM_000212.2:c.428T>G replaces the leucine residue with a tryptophan residue (p.Leu143Trp). This variant has been observed in homozygosity in at least 14 individuals reported to have Glanzmann's thrombasthenia (GT) (PMID: 9376589, PMID: 26096001, PMID: 16463284, PMID: 36672149; PM3). PMID: 16463284 suggests this variant is a founder variant in Indian populations. At least one patient has a phenotype specific for GT (Patient MK, PMID: 9376589) with a history of bleeding and impaired aggregation to at least two agonists, but normal or only mildly reduced agglutination with ristocetin. Additionally, flow cytometry showed <10% expression of αIIbβ3 (PP4_Moderate). This variant has also been observed to segregate with disease in two affected family members (Patients L and M, PMID: 26096001; PP1). Additionally, in silico tools predict the variant is damaging to protein function (REVEL score 0.98; PP3) and transient expression of ITGB3 carrying the variant in 293 cells led to a reduced level of αIIbβ3 and αIIb receptor expression on the cell surface (<5% compared to cells expressing wild type ITGB3, PMID: 11806996; PS3). The highest population minor allele frequency in gnomAD v4.1.0 is 0.00009881 (9/91082 alleles) in the South Asian population, which is lower than the ClinGen PD VCEP threshold (<0.0001; PM2_Supporting). In summary, this variant meets criteria to be classified as pathogenic for GT. GT-specific criteria applied: PS3, PP4_moderate, PP1, PP3, PM2_supporting, PM3.