DOUBLE HETEROZYGOSITY OF THE GPIIB GENE IN A SWISS PATIENT WITH GLANZMANNS-THROMBASTHENIA

Glanzmann's thrombasthenia (GT) results from a qualitative or quantita tive defect of GPIIb-IIIa complexes (integrin alpha(IIb)beta(3)) the f ibrinogen receptor on platelets. This integrin plays a critical role i n platelet aggregation. In this report we describe the molecular abnor malities of a patient with clinical and laboratory findings typical of type I Glanzmann's thrombasthenia, SDS-PAGE with Western blotting rev ealed an absence of GPIIb but small amounts of normally migrating GPII Ia in his platelets. A non-radioactive PCR-SSCP procedure and direct s equence analysis of PCR-amplified DNA fragments showed the patient to be a compound heterozygote for mutations in the GPIIb gene. A single p oint mutation ((; to A) at nucleotide 1064 of the cDNA derived from th e mother's allele led to a Glu(324) to Lys amino acid substitution in GPIIb. It was responsible for a MscI restriction site in exon 12 of th e GPIIb gene, This amino acid substitution changes the electric charge between the second and third Ca++-binding domains of GPIIb. The secon d mutation was inherited from his father and is in exon 18 of the GPII b gene. It was a T --> C base transition at position 1787 of GPIIb cDN A and results in a Ile(565) to Thr substitution. The two GPIIb mutatio ns identified in this study will provide new information on GPIIb-IIIa structure and biosynthesis.