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Study of patients with suspected platelet-based bleeding disorders: a search for patients with a defect in the P2Y12 ADP receptor

Dawood, Ban Behnam (2010)
Ph.D. thesis, University of Birmingham.

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Abstract

Mild platelet-based bleeding disorders are among the most complex bleeding disorders to understand, due to the absence of a ‘gold standard’ test for diagnosis and the significant overlap with the bleeding phenotype observed in healthy individuals. The work in this thesis is focussed on patients with a clinically diagnosed mild platelet disorder for which no acquired cause was identified by the referring expert clinician. ADP and thromboxane A2 (TxA2) are key secondary mediators of platelet aggregation and function in synergy to facilitate robust platelet activation in the event of vascular damage. Less than ten function-disrupting inherited gene defects in the ADP P2Y12 receptor and only one in the platelet TxA2 receptor have been reported, with none in the UK. Over a period of nearly 4 years, patients with a diagnosis of platelet dysfunction made at UK Comprehensive Haemophilia Care Centres were investigated using platelet aggregation and secretion assays alongside controls and reference curves to nine platelet agonists to exhibit an abnormal bleeding phenotype in response to different platelet agonists, focusing in searching on P2Y12 receptor defects. In addition, the P2Y12 ADP receptor from 140 subjects diagnosed with mild type 1 von Willebrand Disease (VWD) from the EU MCMDM-1VWD study was sequenced in view of the similarity in bleeding phenotype of patients with type 1 VWD and mild platelet disorders and the fact that both conditions show incomplete penetrance consistent with a multifactorial basis for each disorder. The sequencing was performed by Dr Martina Daly in Sheffield. The work in this thesis has led to the identification / characterisation of a patient who is homozygous for an early missense mutation in the P2Y12 ADP receptor and two patients with heterozygous point mutations in the P2Y12 ADP receptor (who also has type 1VWD) and in the TxA2 receptor. In addition, I studied platelet aggregation and secretion, along with a number of more specialised assays, in nearly 80 other patients during the course of the thesis and have subdivided these on the basis of the observed defect. Interestingly, in nearly one third of the patients, a platelet defect was not found.

Type of Work:Ph.D. thesis.
Supervisor(s):Watson, Steve P
School/Faculty:Colleges (2008 onwards) > College of Medical & Dental Sciences
Department:School of Clinical and Experimental Medicine
Subjects:RD Surgery
RC Internal medicine
Institution:University of Birmingham
ID Code:1519
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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