A Novel Missense Mutation in ITGB3 Gene Causing Autosomal Dominant Glanzmann Thrombasthenia

Scientific Research Question: The platelet integrin αIIbβ3 is essential for platelet aggregation. A complete loss of this integrin expression usually cause autosomal recessive Glanzmann thrombasthenia. Rarely, ITGB3 gene mutations may cause autosomal dominant macrothrombocytopenia. Here we report a 4-generation pedigree including ten individuals affected by autosomal dominant macrothrombocytopenia associated with impaired function.

Methodology: Blood count, platelet aggregation, flow cytometry analysis (FACS) with monoclonal antibodies and light microscopy were performed by standard procedures. Genomic DNA of affected individuals and controls were screened with next generation sequencing (NGS) on the Illumina platform. The crystal structures and models corresponding to the platelet integrin αIIbβ3 have been investigated in silico to explain the autosomal dominant effect on a structure functional level.

Findings: Recurrent epistaxis was a predominant clinical sign in the affected persons. Administration of antifibrinolytics was sufficient to stop bleedings. Surgical interventions have been performed usually without platelet concentrates. Affected individuals (six males and four females, age: 3–85 showed decreased platelet counts (17–85x10e9/l). Thrombocytes size was found enlarged (forward scatter in patients: 143–168 and in controls 46–53). Platelet aggregation was severely reduced or absent with ADP (5–10 µM), Adrenalin (5 µM), arachidonic acid, and collagen (20 µg/ml) while agglutination induced by ristocetin (0,5–1,2 mg) was normal or mildly reduced. FACS analysis showed normal expression of glycoprotein Ib/IX, glycoprotein IIb/IIIa, and ɑ-membrane glycoproteins. NGS analysis showed a novel heterozygous missense mutation (new nomenclature: c.[2213T>G];[=], p.(Leu738Arg), old nomenclature: Leu712Arg) in exon 14 of ITGB3 gene. The p.Leu738Arg mutation was not detected in four further family members with regular platelet count and function. In silico analysis suggests a gain of function mechanism brought about by formation of non-native contacts in the presence of substituted positively charged arginine residue.

Conclusions: We identified a novel missense mutation causing autosomal dominant Glanzmann Thrombasthenia. This novel heterozygous integrin β3 missense mutation might contribute to thrombocytopenia most likely through gain-of-function mechanisms.

No conflict of interest has been declared by the author(s).