The NM_000212.3:c.1639T>G variant in ITGB3 is a missense variant predicted to cause substitution of cysteine by glycine at amino acid 547 (p.Cys547Gly). This is a critical cysteine residues for regulation of integrin alphaIIbbeta3 (PMID: 14690453). This variant has been observed in compound heterozygosity in one individual (Patient 3 in PMID: 28748566) in combination with ITGB3 variant c.1192delG (p.Ala398ProfsTer24, provisionally classified as pathogenic by the Platelet Disorders VCEP, trans phase not confirmed). This individual displayed mucocutaneous bleeding and impaired aggregation with all agonists except ristocetin, which is highly specific for Glanzmann thrombasthenia (PP4_Moderate). An additional patient reported in DOI: 10.26502/acmcr.96550268 is compound heterozygous for this variant and the ITGB3 variant c.1552C>T (p.Gln518Ter), classified as pathogenic by the Platelet Disorders VCEP, trans phase confirmed (PM3). The highest population minor allele frequency in gnomAD v4.1 is 0.00001610 (19/1179874 alleles) in the non-Finnish European population, which is lower than the ClinGen Platelet Disorders VCEP threshold (<0.0001; PM2_Supporting). Surface expression of β3 and αIIbβ3 measured by Western blot and flow cytometry (respectively) in HEK293 cells transiently co-transfected with p.Cys547Gly variant β3 and wild type αIIb showed decreased expression at <5%, indicating that this variant impacts protein function (PMID: 25827233) (PS3). Furthermore, the computational predictor REVEL gives a score of 0.993, which is above the ClinGen Platelet Disorders VCEP threshold of >0.7 and predicts a damaging effect on 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: PS3, PM2_Supporting, PM3, PP3, PP4_Moderate. (VCEP specifications version 2)