Abstract
Abstract
The variation in blood cell indices between individuals is to a large extent genetically controlled. In the normal population mean platelet volume (MPV) is inversely correlated with platelet count. We undertook a genome-wide association analysis of MPV on 2.5 million imputed genotypes in 1,475 individuals from the UK Blood Services Common Controls, followed by replication in an additional 7,098 samples from four independent collections. We identified a novel locus on chromosome 7q22.3, in a region frequently deleted in myeloid malignancies, where the lead single nucleotide polymorphism (SNP) had a highly significant association with MPV (average G allele effect size 0.15 log fl, 95% CI 0.0118–0.0174, P-value = 9.5×10−24) and an opposite effect on platelet counts (G allele effect −4.51 109/l, 95% CI −6.112 - −2.900, P-value = 1.46×10−7), but the SNP did not exert an effect on red cell indices. The lead SNP with a minor allele frequency of 0.46 is intergenic between the hypothetical gene FLJ36031 and the PIK3CG gene. There are 6 genes in the 1-Mb window centred around the lead SNP and all but HBP1 are transcribed in megakaryocytes (MKs) and to a variable degree in the other seven blood cell lineages. The formation and regulation of volume of platelets is critically dependent on the interaction of MK-expressed integrins with extracellular matrix proteins like fibrinogen and collagen. This prompted us to analyze, in our platelet function cohort of 500 healthy individuals, the association between the lead SNP and binding of both fibrinogen and annexin V to platelets following activation with the collagen mimetic CRP-XL, both associations were significant, with P-values of 0.05 and 0.003, respectively. In summary, we describe a common SNP associated with differences in volume, count and function of platelets from healthy individuals. Intriguingly, our results indicate that the same 7q22.3 region which is frequently deleted in myeloid malignancies harbours important regulatory elements of several platelet phenotypic traits.