Bleeding Disorder, Platelet-Type, 9
Clinical Features
Nieuwenhuis et al. (1985) described studies of 'the platelets of a patient with a hemorrhagic disorder and an excessively long bleeding time...' No other clinical or genetic details, not even the sex of the patient, were given. They demonstrated deficiency of glycoprotein Ia (ITGA2; 192974), which they proposed is the platelet collagen receptor. GP IIa (ITGB1; 135630) may have also been deficient. GP Ib, the von Willebrand factor receptor, is deficient in the Bernard-Soulier syndrome (BSS; 231200), and GP IIb (607759)-IIIa (173470) is deficient in Glanzmann thrombasthenia (273800). All 3 of these, therefore, are 'receptor diseases.' Nieuwenhuis et al. (1986) found that platelets from the patient reported by Nieuwenhuis et al. (1985) showed almost complete absence of adherence to subendothelium and to purified human collagen type III in a perfusion system under flow conditions. The few platelets that did adhere remained in the contact stage without subsequent spreading or aggregate formation. The findings indicated that the bleeding disorder and prolonged bleeding time in the patient were due to a specific defect in the platelet-vessel wall interaction.
Noris et al. (2006) reported 2 unrelated families with a mild bleeding tendency associated with mild thrombocytopenia and normal platelet size. The phenotype was characterized by easy bruising, but no bleeding after surgery or tooth extraction. Mild thrombocytopenia was present since childhood. All patients had prolonged bleeding time. Flow cytometric analysis showed that the platelets had a decreased amount of GP Ia, and GP Ia deficiency was associated with severely reduced in vitro platelet adhesion to molecules known to interact selectively with GP Ia. In vitro platelet aggregation in response to fibrillar collagen was decreased in one family, but normal in the other. Noris et al. (2006) postulated that binding of other platelet receptors to collagen may have masked the GP Ia deficiency. All affected individuals also showed a mild deficiency of alpha-granules. No mutations were found in the ITGA2 or ITGB1 genes.
InheritanceThe transmission pattern of GP Ia deficiency in the families reported by Noris et al. (2006) was consistent with autosomal dominant inheritance.