A novel (288delC) mutation in exon 2 of GPIIb associated with type I Glanzmann's thrombasthenia

This work reports the molecular genetic analysis of two patients who suffer mucocutaneous haemorrhages, prolonged bleeding time and failure of platele ts to aggregate, either spontaneously or in response to agonists. The absen ce of platelet surface glycoprotein (GP)IIb-IIIa complexes confirmed the cl inical diagnosis of Glanzmann's thrombasthenia (GT). Polymerase chain react ion single-strand conformation polymorphism (PCR-SSCP) analysis of exon 2 o f GPIIb showed polymorphic bands caused by the homozygous deletion of a cyt osine at position 288 relative to the translation start site, causing a shi fting of the reading frame and appearance of a premature termination codon. The heterozygous relatives showed a reduced platelet content of GPIIb-IIIa , and a correlation was found between the levels of GPIIb mRNA and surface expression of GPIIb-IIIa complexes. Unlike other mRNAs carrying a nonsense mutation, (288Cdel)GPIIb, does not farce alternative splicing of GPIIb mRNA . As expected, co-transfection of Chinese hamster ovary (CHO) cells with cD NAs encoding GPIIIa and (288delC)GPIIb failed to enhance the surface exposu re of GPIIIa. It is concluded that the (288delC)GPIIb mutation is responsib le for the thrombasthenic phenotype of the patients. In addition, it has al so been determined that heterodimerization of GPIIb-IIIa requires the integ rity of exons 2 and 3 of GPIIb.