A Leu55 to Pro substitution in the integrin alphaIIb is responsible for a case of Glanzmann's thrombasthenia

Glanzmann's thrombasthenia (GT) is a hereditary bleeding disorder caused by a quantitative or qualitative defect in the integrin alphaIIbbeta3. A new mutation, a T to C substitution at base 258 in the alphaIIb gene, leading to the replacement of Leu55 with Pro, was found by sequence analysis of a patient's alphaIIb cDNA. In transfection experiments using COS7 cells, the cells co-transfected with the mutated alphaIIb cDNA containing C258 and wild-type beta3 cDNA scarcely expressed the alphaIIbbeta3 complex. The Leu55 to Pro substitution in the alphaIIb gene was found to be responsible for this case of Glanzmann's thrombasthenia.

Insertion of a C in the exon 28 of integrin alphaIIb 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 alphaIIbbeta3.

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 mRNA encoding for alphaIIb and beta3 were analyzed by the dye-terminator cycle sequencing method. For transfection experiments, expression vectors encoding for wild-type alphaIIb, mutated alphaIIb, beta3, green fluorescent protein (GFP) fusion wild-type alphaIIb, GFP fusion mutated alphaIIb and DsRed fusion beta3 were constructed. These vectors were transfected to COS-7 cells, and the expression levels were determined.

RESULTS

The alphaIIb protein was remarkably reduced in the patient's platelets, and gene analysis showed that the patient possessed compound heterozygous mutations in the alphaIIb 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 alphaIIb containing InsC had expressed and formed a complex with beta3, 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.

Glanzmann's thrombasthenia due to a point mutation within intron 10 results in aberrant splicing of the beta3 gene

Glanzmann's thrombasthenia (GT) is an hereditary bleeding disorder caused by a quantitative or qualitative defect in the integrin alphaIIbbeta3. We attempted to identify genetic defects responsible for a case of GT in Korea. The patient was a 6-year-old boy who had suffered from hemorrhage and purpura. The cDNAs of alphaIIb and beta3 were amplified by reverse transcription (RT)-PCR and were sequenced. RT-PCR of COS7 cells transfected with Exontrap vectors containing the beta3 genomic DNA fragments were performed to verify an aberrant splicing. Transient expression of alphaIIbbeta3 on transfected-COS7 cells was determined by flow cytometry, and the presence of alphaIIbbeta3 was confirmed by immunoprecipitation. We discovered an abnormality with the insertion of 38 bp between exon 10 and exon 11, including a stop codon, in beta3 cDNA. Sequence analysis of genomic DNA showed a point mutation, G-->T, at the position 29 107 of intron 10. RT-PCR analyses of COS7 cells transfected with Exontrap vector containing the mutant beta3 gene revealed that the point mutation at the position 29 107 of intron 10, G-->T, was responsible for an aberrant splicing in the beta3 gene. The transfection experiments and immunoprecipitation revealed the absence of alphaIIbbeta3 in the COS7 cells transfected with mutant gene. The mutation at the position 29 107 of intron 10, G-->T, in the beta3 genomic DNA was found to induce an aberrant splicing and to be responsible for GT in this patient.

Real-time measurement of platelet shape change by light scattering under riboflavin and ultraviolet light treatment

BACKGROUND

The adoption of pathogen reduction technologies (PRTs) is considered for the implementation of safer platelet (PLT) transfusion. However, the effects of PRT treatment including irradiation with ultraviolet (UV) light on PLT shape have not yet been fully clarified.

STUDY DESIGN AND METHODS

Leukoreduced PLT concentrates (PCs) were treated with riboflavin and UV light (Mirasol PRT, TerumoBCT). PLT shape and adenosine diphosphate (ADP)-induced shape change were evaluated by a light scattering method where the amplitude of the scattered signal intensity was measured as the indicator of the proportion of discoid PLTs. Using a modified fluorometer, the real-time effects of different wavelengths of UV light on PLT shape were examined over the range of 300 to 360 nm at the same dose.

RESULTS

The proportion of discoid PLTs in the Mirasol PRT-treated PCs decreased immediately after treatment. The difference in the proportion between PRT-treated and untreated PLTs became larger with storage. Although this modification correlated significantly with the pH decrease and P-selectin expression, the Mirasol PRT-treated PLTs retained sufficient ability to undergo an ADP-induced shape change. In the study using the modified fluorometer, the proportion of discoid PLTs significantly decreased with the wavelength (< 320 nm) of irradiated UV light.

CONCLUSION

Mirasol PRT treatment of PCs decreases the proportion of discoid PLTs, which seemed to be caused by the irradiation with UV light of short wavelengths (< 320 nm), not that of long wavelengths (≥ 320 nm) in the Mirasol PRT system. Modification of UV light wavelength may improve the quality of PRT-treated PCs.