Dynamic and functional linkage between von Willebrand factor and ADAMTS-13 with aging: an Atherosclerosis Risk in Community study.

BACKGROUND: von Willebrand factor (VWF) is a multimeric glycoprotein critically involved in hemostasis, thrombosis, and inflammation. VWF function is regulated by its antigen levels, multimeric structures, and the state of enzymatic cleavage. Population studies in the past have focused almost exclusively on VWF antigen levels in cross-sectional study designs. OBJECTIVE: To identify subjects in the Atherosclerosis Risk in Community study who had persistently low and high VWF antigen over 10 years and to quantify longitudinal changes in the biological activities and cleavage of VWF in these subjects. METHODS: We measured VWF antigen, propeptide, adhesive activities, and cleavage by ADAMTS-13 quantified using a mass spectrometry method that detected the cleaved VWF peptide EQAPNLVY, as well as coagulation factor VIII activity. RESULTS: We determined the mean subject-specific increase in VWF to be 22.0 International Units (IU)/dL over 10 years, with 95% between -0.3 and 59.7 IU/dL. This aging-related increase was also detected in VWF propeptide levels, ristocetin cofactor activity, and VWF binding to collagen. We identified 4.1% and 25.0% of subjects as having persistently low (<50 IU/dL) and high (>200 IU/dL) VWF antigen, respectively. Subjects with persistently low VWF had enhanced ristocetin cofactor activity, whereas those with persistently high VWF had elevated levels of ADAMTS-13, resulting in a comparable rate of VWF cleavage between the 2 groups. CONCLUSIONS: These results provide new information about the effects of aging on VWF antigens and adhesive activity and identify a functional coordination between VWF and the rate of its cleavage by ADAMTS-13.

The utility of 'home-made' reagent red blood cells for antibody screening during pre-transfusion compatibility testing in Uganda.

BACKGROUND: The WHO recommends that pre-transfusion testing should include ABO/RhD grouping followed by screening for red blood cell (RBC) alloantibodies using the indirect antiglobulin test (IAT). However, in Uganda, current practice does not include RBC alloantibody screening. OBJECTIVE: To assess the utility of 'home-made' reagent RBCs in alloantibody screening. MATERIALS AND METHODS: In a laboratory-based study, group O RhD positive volunteer donors were recruited and their extended phenotype performed for C, c, E, e, K, Fya, Fyb Jkb, S and s antigens. These 'home-made' reagent RBCs were preserved using Alsever's solution and alloantibody detection tests performed. For quality assurance, repeat alloantibody screening of patients' samples was done at Bloodworks Northwest Laboratory in Seattle, United States. RESULTS: A total of 36 group O RhD positive individuals were recruited as reagent RBC donors (median age, 25 years; range, 21 - 58 years; male-to-female ratio, 1.6:1). Out of the 311 IATs performed, 32 (10.3%) were positive. Confirmatory IAT testing in the United States was in agreement with the findings in Uganda. CONCLUSION: Use of 'home-made' reagent RBCs during pre-transfusion testing in Uganda is feasible. We recommend the introduction of pre-transfusion IAT alloantibody screening in Uganda using 'home-made' reagent RBCs to improve transfusion safety.

Classification of major and minor blood group antigens in the Kuwaiti Arab population.

Ethnic differences in blood group frequencies might result in clinically important mismatches for transfusions. Arab people represent a large population for which no comprehensive database of red cell genotypes is available and Kuwaitis are no exception. For instance, the Rh blood group is the most elaborate blood group system that shows a high degree of polymorphism among different ethnic groups, there has been little classification of RH alleles in Arab people. Blood samples from 917 Kuwaiti Arab donors in the Kuwaiti Bone Marrow registry were tested with a single-nucleotide polymorphism DNA array. Blood group antigen prevalence were compared to known prevalence in European populations. Multiple subjects were found to be antigen negative for certain phenotypes that is considered rare by the American Rare Donor Program; (Fy(a-,b-) and Kell). In the minor blood group antigens, the FYA allele was predicted to be low in Kuwaitis, when compared to other published accounts. The frequencies of MNS blood antigens in the study population were not significantly different from those reported for European/Caucasian populations. The predicted frequency of the Diego blood group antigen was similar to that observed in a South Asian population. The weak D 1, 2, 3 phenotypes were not prevalent in the Kuwaiti Arab population; however, other RHD variants were detected. We provided information about blood group antigens in the Kuwaiti population that is important for guiding transfusion care. Several interesting findings demonstrated clinical importance, which could be useful in developing transfusion medicine policies and approaches.

Genomic characterization of the RH locus detects complex and novel structural variation in multi-ethnic cohorts.

PURPOSE: Rh antigens can provoke severe alloimmune reactions, particularly in high-risk transfusion contexts, such as sickle cell disease. Rh antigens are encoded by the paralogs, RHD and RHCE, located in one of the most complex genetic loci. Our goal was to characterize RH genetic variation in multi-ethnic cohorts, with the focus on detecting RH structural variation (SV). METHODS: We customized analytical methods to estimate paralog-specific copy number from next-generation sequencing (NGS) data. We applied these methods to clinically characterized samples, including four World Health Organization (WHO) genotyping references and 1135 Asian and Native American blood donors. Subsequently, we surveyed 1715 African American samples from the Jackson Heart Study. RESULTS: Most samples in each dataset exhibited SV. SV detection enabled prediction of the immunogenic RhD and RhC antigens in concordance (>99%) with serological phenotyping. RhC antigen expression was associated with exon 2 hybrid alleles (RHCE*CE-D(2)-CE). Clinically relevant exon 4-7 hybrid alleles (RHD*D-CE(4-7)-D) and exon 9 hybrid alleles (RHCE*CE-D(9)-CE) were prevalent in African Americans. CONCLUSION: This study shows custom NGS methods can accurately detect RH SV, and that SV is important to inform prediction of relevant RH alleles. Additionally, this study provides the first large NGS survey of RH alleles in African Americans.

Safety evaluation of a lyophilized platelet-derived hemostatic product.

BACKGROUND: Hemorrhage causes significant morbidity and mortality in people aged <65 years. A lyophilized platelet-derived hemostatic agent (Thrombosomes) demonstrated hemostatic efficacy in animal models. We report the results of the first safety trial of autologous Thrombosomes given to normal subjects. STUDY DESIGN AND METHODS: Ten subjects received autologous Thrombosomes prepared from their apheresis platelets, and five control subjects received a buffer solution. There were five cohorts, with three subjects per cohort (two in the Thrombosomes group and one in the control group). Doses escalated from 1/1,000 to 1/10 of a proposed efficacious dose. Cohorts 4 and 5 received the highest dose, but in Cohort 5, one-half the dose was infused 2 hours apart. Cohorts 1 through 3 were monitored for 42 days, Cohorts 4 and 5 were monitored for 60 days using hematology, coagulation, and chemistry assays and antibody testing. RESULTS: There were no serious adverse events (AEs) and no subject withdrawals. There were eight treatment-related AEs (TRAEs) in 5 of 15 subjects (33%) (four in the Thrombosomes group and one in the control group). Of four subjects receiving the highest doses, three had TRAEs. One had elevated D-dimer, prothrombin fragment 1 + 2, and white blood cell count (subject had concurrent upper respiratory tract infection); one had T-wave inversions in precordial leads V2 and V3 without elevated troponin or symptoms; and one had a platelet autoantibody without change in platelet count. All subjects' TRAEs resolved by Day 21. CONCLUSION: There were no serious AEs in this small study. Thrombosomes were considered safe at the doses assessed. Future, larger trials will be needed to further assess safety and efficacy.

Implication of antibodies against human leukocyte antigen in simultaneous presentation of fetal and neonatal alloimmune thrombocytopenia and neutropenia.

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) and neonatal alloimmune neutropenia (NAN) are two rare complications of newborns caused by antibodies against paternal inherited antigens. Human platelet (HPA) and neutrophil antigens (HNA) are the common targets. Human leukocyte antigen (HLA) class I proteins are also expressed on platelets and neutrophils and anti-HLA antibodies have occasionally been implicated in these complications. We report a premature twin infant who presented with severe thrombocytopenia and neutropenia clinically compatible with FNAIT and NAN, from a mother with no identifiable HPA or HNA antibodies, but with very high levels of complement-fixing antibodies against paternal inherited HLA. These antibodies were also detected in the infant. HLA antibodies are commonly present in multiparous women who deliver healthy infants. They can, however, be cytotoxic and cause clinical complications after blood products transfusion (TRALI and becoming refractory to platelets transfusion) and after organ transplantation (allogeneic organ rejection).

Red blood cell antigen genotype analysis for 9087 Asian, Asian American, and Native American blood donors.

BACKGROUND: There has yet to be a comprehensive analysis of blood group antigen prevalence in Asian Americans and Native Americans. There may be ethnic differences in blood group frequencies that would result in clinically important mismatches through transfusion. STUDY DESIGN AND METHODS: Blood donors who self-identified as Asian or Native American were tested using a single-nucleotide polymorphism (SNP) DNA array (HEA BeadChip kit, Bioarray Solutions Ltd) that predicts expression of 38 human erythrocyte antigens (HEAs) and by serology for ABO, D, C, M, N, Jk(a) , and Jk(b) . The prevalence of blood group antigens was compared to published European prevalence. Discrepancies between SNP-predicted and serology-detected antigens were tallied. RESULTS: A total of 9087 blood donors were tested from nine Asian and Native American heritages. The predicted prevalence of selected antigens in the RHCE, JK, FY, MNS, LU, CO, and DO blood group systems were variable between Asian populations, but overall not significantly different than Europeans. Compared to European frequencies, Kell blood group allele frequencies were significantly different in the Chinese, Native American, Hawaiian/Pacific Islander, South Asian, and Southeast Asian heritage blood donors; Diego antigens Di(a) and Di(b) were different in donors of Native American and South Asian ancestries (p < 0.05). Of the donors tested, 4.5% showed a SNP-serology discrepancy that segregated within specific ethnic groups. CONCLUSION: This study provides HEA allele frequency and antigen prevalence data in a cohort of Asian and Native Americans donors. Several ethnic groups exhibited differences in HEA frequencies compared to Europeans. Genotype-serotype discrepancies were detected in all systems studied.

Complex changes in von Willebrand factor-associated parameters are acquired during uncomplicated pregnancy.

BACKGROUND: The coagulation protein von Willebrand Factor (VWF) is known to be elevated in pregnancy. However, the timing and nature of changes in VWF and associated parameters throughout pregnancy are not well understood. OBJECTIVES: To better understand the changes in VWF provoked by pregnancy, we studied VWF-associated parameters in samples collected over the course of healthy pregnancies. METHODS: We measured VWF antigen (VWF:Ag), VWF propeptide (VWFpp), Factor VIII (FVIII), and ADAMTS13 activity in samples collected from 46 women during pregnancy and at non-pregnant baseline. We also characterized pregnant vs. non-pregnant VWF multimer structure in 21 pregnancies, and performed isoelectric focusing (IEF) of VWF in two pregnancies which had samples from multiple trimesters. RESULTS: VWF:Ag and FVIII levels were significantly increased during pregnancy. ADAMTS13 activity was unchanged. VWFpp levels increased much later in pregnancy than VWF:Ag, resulting in a progressive decrease in VWFpp:Ag ratios. FVIII:VWF ratios also decreased in pregnancy. Most pregnancies exhibited a clear loss of larger VWF multimers and altered VWF triplet structure. Further evidence of acquired VWF qualitative changes in pregnancy was found in progressive, reversible shifts in VWF IEF patterns over gestation. CONCLUSIONS: These data support a new view of pregnancy in which VWF can acquire qualitative changes associated with advancing gestational age. Modeling supports a scenario in which both increased VWF production and doubling of the VWF half-life would account for the data observed. We propose that gestation induces a prolongation in VWF survival, which likely contributes to increased total VWF levels and altered VWF structure.

Molecular blood typing augments serologic testing and allows for enhanced matching of red blood cells for transfusion in patients with sickle cell disease.

BACKGROUND: Sickle cell disease (SCD) patients have dissimilar red blood cell (RBC) phenotypes compared to the primarily Caucasian blood donor base due, in part, to underlying complex Rh and silenced Duffy expression. Gene array-based technology offers high-throughput antigen typing of blood donors and can identify patients with altered genotypes. The purpose of the study was to ascertain if RBC components drawn from predominantly Caucasian donors could provide highly antigen-matched products for molecularly typed SCD patients. STUDY DESIGN AND METHODS: SCD patients were genotyped by a molecular array (HEA Beadchip, BioArray Solutions). The extended antigen phenotype (C, c, E, e, K, k, Jk(a) , Jk(b) , Fy(a) , Fy(b) , S, s) was used to query the inventory using different matching algorithms; the resulting number of products was recorded. RESULTS: A mean of 96.2 RBC products was available for each patient at basic-level, 34 at mid-level, and 16.3 at high-level stringency. The number of negative antigens correlated negatively with the number of available products. The Duffy silencing mutation in the promoter region (67T>C) (GATA) was found in 96.5% of patients. Allowing Fy(b+) products for patients with GATA increased the number of available products by up to 180%, although it does not ensure prevention of Duffy antibodies in all patients. CONCLUSIONS: This feasibility study provides evidence that centers with primarily Caucasian donors may be able to provide highly antigen-matched products. Knowledge of the GATA status expands the inventory of antigen-matched products. Further work is needed to determine the most clinically appropriate match level for SCD patients.

Diabetes duration may modify the association between genetic variation in the glycoprotein Ia subunit of the platelet collagen receptor and risk of severe diabetic retinopathy: a working hypothesis.

Genetic factors appear to contribute to the severity and progression of diabetic retinopathy. We assessed the associations of the C807T and Glu505Lys variants of the glycoprotein Ia (alpha(2) integrin) subunit of the platelet/endothelial collagen receptor and risk of retinopathy in a population-based survey of 288 diabetic patients in one Swedish community. Neither variant was associated with retinopathy risk overall. However, the 807T variant was associated with increased risk of severe retinopathy, and the association was modified by diabetes duration. Among patients with diabetes of longer duration (>/=25 years), the 807T variant was strongly associated with risk of severe retinopathy (odds ratio 7.49, 95% confidence interval 1.75 to 32.1). There was no association between the 807T variant and risk of severe retinopathy among patients with diabetes duration <25 years. The Lys505 variant of glycoprotein Ia was associated with an odds ratio for severe retinopathy of 1.88 (95% confidence interval 0.83 to 4.24). Overall, there was a significant interaction between glycoprotein Ia genotype and duration of diabetes on the risk of retinopathy (P-value for interaction = 0.019). These results suggest the hypothesis that genetic variation of platelet glycoprotein Ia may play a particularly important role during the advanced stages of diabetic retinopathy.

Coagulation factor XIII polymorphisms and the risk of myocardial infarction and ischaemic stroke in young women.

The inconsistent findings among association studies that have examined the relationship between factor XIIIA Val34Leu and thrombosis may be owing to (1) population differences in the prevalence of other risk factors that modify the association with Val34Leu, or (2) linkage disequilibrium with other functional factor XIIIA polymorphisms. We therefore performed genotyping for factor XIIIA Val34Leu, Tyr204Phe and Pro564Leu in a population-based study of myocardial infarction (MI) and ischaemic stroke among white women <45-years of age and 345 demographically similar controls, and examined potential interactions with other risk factors. The presence of the factor XIIIA Leu34 allele was associated with a slight decreased risk of MI [odds ratio (OR) = 0.80] that was most pronounced among women with traditional cardiovascular risk factors. Paradoxically, women carrying two copies of the Leu34 allele had a nearly fourfold increased risk of ischaemic stroke relative to the Val34/Val34 genotype. Heterozygosity for factor XIIIA Phe204 was associated with a milder increased risk of ischaemic stroke, and analysis of a kindred with congenital dysfibrinogenaemia suggested that co-inheritance of the factor XIIIA Phe204 allele may increase susceptibility to ischaemic stroke. Our results suggest that the factor XIIIA Val34Leu variant may be associated with a decreased risk of MI among young women with other risk factors. The relationship of factor XIIIA polymorphisms to cerebrovascular disease requires further study.