Insertion of a C in the exon 28 of integrin αIIb gene leading to a frameshift mutation is responsible for Glanzmann thrombasthenia in a Japanese case

Background: Glanzmann thrombasthenia (GT) is a hereditary bleeding disorder caused by a qualitative or quantitative defect in the integrin alpha IIb beta 3. Objective: Our objective is to identify the gene mutation that resulted in GT. Patients and methods: The patient was a 66-year-old male with a history of frequent bleeding. The expression levels of the integrin proteins in the platelets were determined by flow cytometry and Western blot analysis. The sequences of genomic DNA and rnRNA encoding for alpha IIb and beta 3 were analyzed by the dye-terminator cycle sequencing method. For transfection experiments, expression vectors encoding for wild-type alpha IIb, mutated alpha IIb, beta 3, green fluorescent protein (GFP) fusion wild-type alpha IIb, GFP fusion mutated alpha IIb and DsRed fusion P3 were constructed. These vectors were transfected to COS-7 cells, and the expression levels were determined. Results: The alpha IIb protein was remarkably reduced in the patient's platelets, and gene analysis showed that the patient possessed compound heterozygous mutations in the alpha IIb gene. One was a C->G Substitution at the splice acceptor site (-3) of exon 26 (CAG->GAG) and the other was the insertion of an additional C at the region including six C bases between 2911 and 2916 in exon 28 (InsC). Transfection experiments using COS-7 cells showed that alpha IIb containing InsC had expressed and formed a complex with beta 3, but had not been transported to the Golgi apparatus. Conclusions: In the present study the novel mutation InsC, leading to a frameshift that affects the transmembrane domain and the cytoplasmic tail, was found to be responsible for GT.