A novel (288delC) mutation in exon 2 of GPIIb associated with type I Glanzmann's thrombasthenia.
ABSTRACT This work reports the molecular genetic analysis of two patients who suffer mucocutaneous haemorrhages, prolonged bleeding time and failure of platelets to aggregate, either spontaneously or in response to agonists. The absence of platelet surface glycoprotein (GP)IIb-IIIa complexes confirmed the clinical diagnosis of Glanzmann's thrombasthenia (GT). Polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) analysis of exon 2 of GPIIb showed polymorphic bands caused by the homozygous deletion of a cytosine at position 288 relative to the translation start site. causing a shifting 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 force alternative splicing of GPIIb mRNA. As expected, co-transfection of Chinese hamster ovary (CHO) cells with cDNAs encoding GPIIIa and (288delC)GPIIb failed to enhance the surface exposure of GPIIIa. It is concluded that the (288delC)GPIIb mutation is responsible for the thrombasthenic phenotype of the patients. In addition, it has also been determined that heterodimerization of GPIIb-IIIa requires the integrity of exons 2 and 3 of GPIIb.
Article: Type II Glanzmann thrombasthenia in a compound heterozygote for the alpha IIb gene. A novel missense mutation in exon 27.[show abstract] [hide abstract]
ABSTRACT: Glanzmann thrombasthenia is an autosomal recessive bleeding disorder characterized by a life-long hemorrhagic tendency and absent or severely reduced platelet aggregation in response to agonists, caused by quantitative or qualitative abnormalities in the platelet fibrinogen receptor, integrin alphaIIb beta3. The aim of this study was to identify the molecular genetic defect and determine its functional consequences in a patient with type II Glanzmann thrombasthenia. The expression of platelet alphaIIb beta3 was determined by flow cytometry and western blotting. Mutations were identified by sequencing both cDNA and genomic DNA. Functional characterization was assessed by exontrap and transient transfection analysis. Flow cytometry and western blot analysis revealed markedly reduced levels of platelet alphaIIb beta3, which may account for the residual fibrinogen binding detected upon platelet activation. Sequencing of genomic DNA revealed the presence of two mutations in the alphaIIb gene: a C1750T transition in the last codon of exon 17 changing Arg553 to STOP, and a C2829T transition in exon 27 that changes Pro912 to Leu. Sequence analysis of reversely transcribed alphaIIb mRNA did not detect cDNA from the C1750T mutant allele, and revealed a significant increase of the physiological splicing out of exon 28 in the cDNA carrying the C2829T mutation. Transient expression of [912Leu]alphaIIb in CHO-b3 cells showed a marked reduction in the rate of surface expression of alphaIIb beta3. The results suggest that the thrombasthenic phenotype is the result of reduced availability of alphaIIb-mRNA, enhanced expression of exon 28-deleted transcripts, and defective processing of [912Leu]alphaIIb.Haematologica 11/2006; 91(10):1352-9. · 6.42 Impact Factor