Glanzmann thrombasthenia and Bernard-Soulier syndrome in south Iran

Glanzmann thrombasthenia (GT) and Bernard-Soulier syndrome (BSS) are two rare inherited disorders of platelet function. In this study, we report the demographic, clinical and biological characteristics of 23 patients with GT and of seven patients with BSS from southern Iran who had been followed for many years but fully characterized only recently, when platelet aggregation tests and flow cytometric studies became available for the first time in the country. We found a high prevalence of both diseases that can be explained by the high rate of consanguineous marriages in south Iran. Patients affected by GT and BSS suffer mainly from mucocutaneous bleedings causing anemia and transfusion requirements.

[Genetic profile of Glanzmann's thrombasthenia in south Tunisia. Report of 17 cases (11 families)]

INTRODUCTION

Glanzmann's thrombasthenia (GT) is a rare congenital thrombopathy, with a recessive autosomal transmission. We present here the genealogic study of a series of patients suffering from GT.

PATIENTS AND METHODS

This is a retrospective study about all the GT patients treated in Sfax hematology department during 18 years. Final diagnosis was established by agregometry. Genealogic study was based on clinical history.

RESULTS

17 cases of GT from 11 families from the south of Tunisia wen collected. The disease was paricularly frequent in the region of Moulares-Gafsa (7 patients). The percentage of consanguinity was also very high (82%), with a third degree consanguinity of 86%. Family investigation revealed 6 previously unknown cases, and 10 deaths subsequent to hemorrhagic manifestations.

CONCLUSION

The high rate of consanguinity, the absence of clinical or biological manifestations in the parents, and the ratio of ill to normal subjects in the same family which was about one to four, are suggestive of an autosomal recessive mode of transmission.

Presentation and pattern of symptoms in 382 patients with Glanzmann thrombasthenia in Iran

Glanzmann thrombasthenia (GT) is a rare autosomal recessive disease characterized by prolonged bleeding time with normal platelet count and morphology. It is caused by the quantitative or qualitative deficiency of the platelet glycoprotein IIb-IIIa. In 382 Iranian patients with GT diagnosed at a single center during the period 1969-2001, consanguinity between parents was 86.6%, in accord with the high frequency of intrafamilial marriages in Iran. Almost all patients had had abnormal mucocutaneous bleeding (epistaxis and gum bleeding); at follow-up, 4/5 of the patients had been transfused at least once to control hemorrhagic episodes. As expected, almost all the patients had a normal platelet count while the leukocyte count was increased in 19.3%. Among women, an unexpected low rate of pregnancies was observed.

[Glanzmann's thrombasthenia: a rare example of an integrin deficit]

Glanzmann's thrombasthenia is an autosomal recessive life-long bleeding disorder, originated from a quantitative or qualitative defect of the major platelet membrane receptor: the GPIIb/IIIa complex. The GPIIb/IIIa complex is a calcium-dependent heterodimer, belonging to the integrin superfamily. The complex of activated platelets can bind fibrinogen, von Willebrand factor, fibronectin and vitronectin, which are proteins playing an important role in platelet adhesion and aggregation. Thrombasthenic platelets are deficient in GPIIb, GPIIIa and GPIIb/IIIa complex; however, platelets from few thrombasthenic patients content near-normal amounts of functionally abnormal complex. The GPIIb/IIIa quantitative or functional defect leads to defective platelet hemostatic plug formation. Hemorrhagic symptoms consist of purpura, gingival hemorrhage, menorrhagia and epistaxis. Some cases of Glanzmann's thrombasthenia have been characterized at the molecular genetic level. Molecular abnormalities include: GPIIb or GPIIIa partial gene deletion, GPIIIa gene insertion, a point mutation resulting in an amino acid substitution within the GPIIIa molecule. In spite of the contemporary reduction of both GPIIb and GPIIIa in most cases of Glanzmann's thrombasthenia, it appears that a molecular abnormality affecting only one of the glycoprotein genes may result in a thrombasthenic phenotype.

Biochemical and molecular basis of Glanzmann's thrombasthenia

Glanzmann's thrombasthenia is a rare autosomal recessive bleeding disorder characterized by a quantitative deficiency or a functional abnormality of the major platelet membrane integrin receptor: the glycoprotein (GP) IIb/IIIa complex. The GPIIb/IIIa complex functions as a platelet receptor for fibrinogen, von Willebrand factor, fibronectin and vitronectin; therefore it plays an important role in platelet adhesion and aggregation. Thrombasthenic platelets are severely deficient in GPIIb/IIIa content or function, and fail to aggregate and form the hemostatic plug at the site of vessel injury. On the other hand, heterozygous subjects (having about half the number of normal GPIIb/IIIa complexes) do not show bleeding problems. It has been demonstrated that a molecular defect affecting one of the two GP coding genes is sufficient to determine a contemporary deficit of both GPIIb and GPIIIa, and hence the thrombasthenic phenotype. Up to now, few molecular abnormalities giving rise to Glanzmann's thrombasthenia have been characterized. Large rearrangements within the GPIIb or GPIIIa coding genes appear to be unusual, whereas small modifications in the nucleotide sequence of the coding regions occur with higher frequency.