Nicholas A. Watkins

A genome-wide meta-analysis identifies 22 loci associated with eight hematological parameters in the HaemGen consortium.

The number and volume of cells in the blood affect a wide range of disorders including cancer and cardiovascular, metabolic, infectious and immune conditions. We consider here the genetic variation in eight clinically relevant hematological parameters, including hemoglobin levels, red and white blood cell counts and platelet counts and volume. We describe common variants within 22 genetic loci reproducibly associated with these hematological parameters in 13,943 samples from six European population-based studies, including 6 associated with red blood cell parameters, 15 associated with platelet parameters and 1 associated with total white blood cell count. We further identified a long-range haplotype at 12q24 associated with coronary artery disease and myocardial infarction in 9,479 cases and 10,527 controls. We show that this haplotype demonstrates extensive disease pleiotropy, as it contains known risk loci for type 1 diabetes, hypertension and celiac disease and has been spread by a selective sweep specific to European and geographically nearby populations.

Loss of function of a lupus-associated FcγRIIb polymorphism through exclusion from lipid rafts

Dysfunction of receptors for IgG (FcγRs) has been thought to be involved in the pathogenesis of systemic lupus erythematosus (SLE). We show that a recently described SLE-associated polymorphism of FcγRIIb (FcγRIIbT232), encoding a single transmembrane amino acid substitution, is functionally impaired. FcγRIIbT232 is unable to inhibit activatory receptors because it is excluded from sphingolipid rafts, resulting in the unopposed proinflammatory signaling thought to promote SLE.

Nomenclature of human platelet antigens

1 Division of Haematology, National Institute for Biological Standards and Control, South Mimms, Potters Bar, UK 2 Department of Haematology, University of Cambridge and National Blood Service Cambridge, Cambridge, UK 3 Platelet Unit, INTS, Paris, France 4 Blood Research Institute, the Blood Center of Southeastern Wisconsin, Milwaukee, Wisconsin, USA 5 Finnish Red Cross Blood Transfusion Service, Helsinki, Finland 6 Sanquin Research at CLB, Amsterdam, the Netherlands 7 Saitama Red Cross Blood Center, Hidaka-Shi, Saitama, Japan 8 McMaster University Medical Centre, Hamilton, Ontario, Canada 9 Department of Transfusion Medicine, University of Rostock, Rostock, Germany 10 Institute for Clinical Immunology and Transfusion Medicine, Justus Liebig University, Giessen, Germany * Chairman of the ISBT platelet working party

Investigation of Crohn's Disease Risk Loci in Ulcerative Colitis Further Defines Their Molecular Relationship

BACKGROUND & AIMS Identifying shared and disease-specific susceptibility loci for Crohns disease (CD) and ulcerative colitis (UC) would help define the biologic relationship between the inflammatory bowel diseases. More than 30 CD susceptibility loci have been identified. These represent important candidate susceptibility loci for UC. Loci discovered by the index genome scans in CD have previously been tested for association with UC, but those identified in the recent meta-analysis await such investigation. Furthermore, the recently identified UC locus at ECM1 requires formal testing for association with CD. METHODS We analyzed 45 single nucleotide polymorphisms, tagging 29 of the loci recently associated with CD in 2527 UC cases and 4070 population controls. We also genotyped the UC-associated ECM1 variant rs11205387 in 1560 CD patients and 3028 controls. RESULTS Nine regions showed association with UC at a threshold corrected for the 29 loci tested (P < .0017). The strongest association (P = 4.13 x 10(-8); odds ratio = 1.27) was identified with a 170-kilobase region on chromosome 1q32 that contains 3 genes. We also found association with JAK2 and replicated a recently reported association with STAT3, further implicating the role of this signaling pathway in inflammatory bowel disease. Additional novel UC susceptibility genes were LYRM4 and CDKAL1. Twenty of the loci were not associated with UC, and several appear to be specific to CD. ECM1 variation was not associated with CD. CONCLUSIONS Collectively, these data help define the genetic relationship between CD and UC and characterize common, as well as disease-specific mechanisms of pathogenesis.

Systemic lupus erythematosus-associated defects in the inhibitory receptor FcγRIIb reduce susceptibility to malaria

Polygenic autoimmune diseases, such as systemic lupus erythematosus (SLE), are a significant cause of morbidity and mortality worldwide. In recent years, functionally important genetic polymorphisms conferring susceptibility to SLE have been identified, but the evolutionary pressures driving their retention in the gene pool remain elusive. A defunctioning, SLE-associated polymorphism of the inhibitory receptor FcγRIIb is found at an increased frequency in African and Asian populations, broadly corresponding to areas where malaria is endemic. Here, we show that FcγRIIb-deficient mice have increased clearance of malarial parasites (Plasmodium chabaudi chabaudi) and develop less severe disease. In vitro, the human lupus associated FcγRIIb polymorphism enhances phagocytosis of Plasmodium falciparum-infected erythrocytes. These results demonstrate that FcγRIIb is important in controlling the immune response to malarial parasites and suggests that the higher frequency of human FcγRIIb polymorphisms predisposing to SLE in Asians and Africans may be maintained because these variants reduce susceptibility to malaria.

Platelet genomics and proteomics in human health and disease

Proteomic and genomic technologies provide powerful tools for characterizing the multitude of events that occur in the anucleate platelet. These technologies are beginning to define the complete platelet transcriptome and proteome as well as the protein-protein interactions critical for platelet function. The integration of these results provides the opportunity to identify those proteins involved in discrete facets of platelet function. Here we summarize the findings of platelet proteome and transcriptome studies and their application to diseases of platelet function.

A novel variant on chromosome 7q22.3 associated with mean platelet volume, counts, and function.

Mean platelet volume (MPV) and platelet count (PLT) are highly heritable and tightly regulated traits. We performed a genome-wide association study for MPV and identified one SNP, rs342293, as having highly significant and reproducible association with MPV (per-G allele effect 0.016 +/- 0.001 log fL; P < 1.08 x 10(-24)) and PLT (per-G effect -4.55 +/- 0.80 10(9)/L; P < 7.19 x 10(-8)) in 8586 healthy subjects. Whole-genome expression analysis in the 1-MB region showed a significant association with platelet transcript levels for PIK3CG (n = 35; P = .047). The G allele at rs342293 was also associated with decreased binding of annexin V to platelets activated with collagen-related peptide (n = 84; P = .003). The region 7q22.3 identifies the first QTL influencing platelet volume, counts, and function in healthy subjects. Notably, the association signal maps to a chromosome region implicated in myeloid malignancies, indicating this site as an important regulatory site for hematopoiesis. The identification of loci regulating MPV by this and other studies will increase our insight in the processes of megakaryopoiesis and proplatelet formation, and it may aid the identification of genes that are somatically mutated in essential thrombocytosis.

A Genome-wide Association Study Identifies Three Loci Associated with Mean Platelet Volume

Mean platelet volume (MPV) is increased in myocardial and cerebral infarction and is an independent and strong predictor for postevent morbidity and mortality. We conducted a genome-wide association study (GWAS), the KORA (Kooperative Gesundheitsforschung in der Region Augsburg) F3 500K study, and found MPV to be strongly associated with three common single-nucleotide polymorphisms (SNPs): rs7961894 located within intron 3 of WDR66 on chromosome 12q24.31, rs12485738 upstream of the ARHGEF3 on chromosome 3p13-p21, and rs2138852 located upstream of TAOK1 on chromosome 17q11.2. We replicated all three SNPs in another GWAS from the UK and in two population-based samples from Germany. In a combined analysis including 10,048 subjects, the SNPs had p values of 7.24 x 10(-48) for rs7961894, 3.81 x 10(-27) for rs12485738, and 7.19 x 10(-28) for rs2138852. These three quantitative trait loci together accounted for 4%-5% of the variance in MPV. In-depth sequence analysis of WDR66 in 382 samples from the extremes revealed 20 new variants and a haplotype with three coding SNPs and one SNP at the transcription start site associated with MPV (p = 6.8 x 10(-5)). In addition, expression analysis indicated a direct correlation of WDR66 transcripts and MPV. These findings may not only enhance our understanding of platelet activation and function, but may also provide a focus for several novel research avenues.

Transcription profiling in human platelets reveals LRRFIP1 as a novel protein regulating platelet function.

Within the healthy population, there is substantial, heritable, and interindividual variability in the platelet response. We explored whether a proportion of this variability could be accounted for by interindividual variation in gene expression. Through a correlative analysis of genome-wide platelet RNA expression data from 37 subjects representing the normal range of platelet responsiveness within a cohort of 500 subjects, we identified 63 genes in which transcript levels correlated with variation in the platelet response to adenosine diphosphate and/or the collagen-mimetic peptide, cross-linked collagen-related peptide. Many of these encode proteins with no reported function in platelets. An association study of 6 of the 63 genes in 4235 cases and 6379 controls showed a putative association with myocardial infarction for COMMD7 (COMM domain-containing protein 7) and a major deviation from the null hypo thesis for LRRFIP1 [leucine-rich repeat (in FLII) interacting protein 1]. Morpholino-based silencing in Danio rerio identified a modest role for commd7 and a significant effect for lrrfip1 as positive regulators of thrombus formation. Proteomic analysis of human platelet LRRFIP1-interacting proteins indicated that LRRFIP1 functions as a component of the platelet cytoskeleton, where it interacts with the actin-remodeling proteins Flightless-1 and Drebrin. Taken together, these data reveal novel proteins regulating the platelet response.

Functional genomics in zebrafish permits rapid characterization of novel platelet membrane proteins.

In this study, we demonstrate the suitability of the vertebrate Danio rerio (zebrafish) for functional screening of novel platelet genes in vivo by reverse genetics. Comparative transcript analysis of platelets and their precursor cell, the megakaryocyte, together with nucleated blood cell elements, endothelial cells, and erythroblasts, identified novel platelet membrane proteins with hitherto unknown roles in thrombus formation. We determined the phenotype induced by antisense morpholino oligonucleotide (MO)–based knockdown of 5 of these genes in a laser-induced arterial thrombosis model. To validate the model, the genes for platelet glycoprotein (GP) IIb and the coagulation protein factor VIII were targeted. MO-injected fish showed normal thrombus initiation but severely impaired thrombus growth, consistent with the mouse knockout phenotypes, and concomitant knockdown of both resulted in spontaneous bleeding. Knockdown of 4 of the 5 novel platelet proteins altered arterial thrombosis, as demonstrated by modified kinetics of thrombus initiation and/or development. We identified a putative role for BAMBI and LRRC32 in promotion and DCBLD2 and ESAM in inhibition of thrombus formation. We conclude that phenotypic analysis of MO-injected zebrafish is a fast and powerful method for initial screening of novel platelet proteins for function in thrombosis.