Joep W. R. Sins

Early occurrence of red blood cell alloimmunization in patients with sickle cell disease

Red blood cell (RBC) alloimmunization is a major complication of transfusion therapy in sickle cell disease (SCD). Identification of high‐risk patients is hampered by lack of studies that take the cumulative transfusion exposure into account. In this retrospective cohort study among previously non‐transfused SCD patients in the Netherlands, we aimed to elucidate the association between the cumulative transfusion exposure, first alloimmunization and independent risk factors. A total of 245 patients received 11 952 RBC units. Alloimmunization occurred in 43 patients (18%), half of them formed their first alloantibody before the 8th unit. In patients with exposure to non‐extended matched transfusions (ABO and RhD) the cumulative alloimmunization risk increased up to 35% after 60 transfused units. This was significantly higher compared to a general transfused population (HR 6.6, CI 4.2–10.6). Receiving the first transfusion after the age of 5 was an independent risk factor for alloimmunization (HR 2.3, CI 1.0–5.1). Incidental, episodic transfusions in comparison to chronic scheme transfusions (HR 2.3, CI 0.9–6.0), and exposure to non‐extended matched units in comparison to extended matching (HR 2.0, CI 0.9–4.6) seemed to confer a higher alloimmunization risk. The majority of first alloantibodies are formed after minor transfusion exposure, substantiating suggestions of a responder phenotype in SCD and stressing the need for risk factor identification. In this study, older age at first transfusion, episodic transfusions and non‐extended matched transfusions appeared to be risk factors for alloimmunization. Am. J. Hematol. 91:763–769, 2016.

Nonallelic homologous recombination of the FCGR2/3 locus results in copy number variation and novel chimeric FCGR2 genes with aberrant functional expression.

The human FCGR2/3 locus, containing five highly homologous genes encoding the major IgG receptors, shows extensive copy number variation (CNV) associated with susceptibility to autoimmune diseases. Having genotyped >4000 individuals, we show that all CNV at this locus can be explained by nonallelic homologous recombination (NAHR) of the two paralogous repeats that constitute the majority of the locus, and describe four distinct CNV regions (CNRs) with a highly variable prevalence in the population. Apart from CNV, NAHR events also created several hitherto unidentified chimeric FCGR2 genes. These include an FCGR2A/2C chimeric gene that causes a decreased expression of FcγRIIa on phagocytes, resulting in a decreased production of reactive oxygen species in response to immune complexes, compared with wild-type FCGR2A. Conversely, FCGR2C/2A chimeric genes were identified to lead to an increased expression of FCGR2C. Finally, a rare FCGR2B null-variant allele was found, in which a polymorphic stop codon of FCGR2C is introduced into one FCGR2B gene, resulting in a 50% reduction in protein expression. Our study on CNRs and the chimeric genes is essential for the correct interpretation of association studies on FCGR genes as a determinant for disease susceptibility, and may explain some as yet unidentified extreme phenotypes of immune-mediated disease.

Nonclassical FCGR2C haplotype is associated with protection from red blood cell alloimmunization in sickle cell disease

Red blood cell (RBC) transfusions are of vital importance in patients with sickle cell disease (SCD). However, a major complication of transfusion therapy is alloimmunization. The low-affinity Fcγ receptors, expressed on immune cells, are important regulators of antibody responses. Genetic variation in FCGR genes has been associated with various auto- and alloimmune diseases. The aim of this study was to evaluate the association between genetic variation of FCGR and RBC alloimmunization in SCD. In this case-control study, DNA samples from 2 cohorts of transfused SCD patients were combined (France and The Netherlands). Cases had a positive history of alloimmunization, having received ≥1 RBC unit. Controls had a negative history of alloimmunization, having received ≥20 RBC units. Single nucleotide polymorphisms and copy number variation of the FCGR2/3 gene cluster were studied in a FCGR-specific multiplex ligation-dependent probe amplification assay. Frequencies were compared using logistic regression. Two hundred seventy-two patients were included (130 controls, 142 cases). The nonclassical open reading frame in the FCGR2C gene (FCGR2C.nc-ORF) was strongly associated with a decreased alloimmunization risk (odds ratio [OR] 0.26, 95% confidence [CI] 0.11-0.64). This association persisted when only including controls with exposure to ≥100 units (OR 0.30, CI 0.11-0.85) and appeared even stronger when excluding cases with Rh or K antibodies only (OR 0.19, CI 0.06-0.59). In conclusion, SCD patients with the FCGR2Cnc-ORF polymorphism have over a 3-fold lower risk for RBC alloimmunization in comparison with patients without this mutation. This protective effect was strongest for exposure to antigens other than the immunogenic Rh or K antigens.

Daily pain in adults with sickle cell disease-a different perspective.

Previous reports demonstrated that patients with sickle cell disease (SCD) experience pain on more than half of the observed days. Yet, these high incidences do not seem to match observations in our population. In this prospective cohort study, we aimed to assess the frequency and characteristics of daily, self‐reported pain among adult SCD patients in the Netherlands. Consecutive patients were enrolled during routine outpatient visits and followed up to 6 months. A total of 55 patients completed 5,982 diary observation days. Median age was 27 years (IQR 23‐43). Patients reported SCD related pain on 17% of the observed days; on 13% of these days this pain was not defined as a painful crisis, while 3% was reported as a painful crisis but managed at home, and on 1% of the observed days patients were admitted to the hospital. Analgesics were used on 52% of days with pain with a relatively infrequent use of oral opioids (9% of pain days). This first European study on pain in SCD indicates that pain appears to be significantly less frequent in our population as compared to previous study cohorts from the United States, and may be more representative for current SCD populations in other Western countries. Besides a more widespread use of hydroxycarbamide in modern disease management, differences in organization and accessibility of healthcare between countries may also explain this discrepancy.

Effect of N-acetylcysteine on pain in daily life in patients with sickle cell disease: a randomised clinical trial

N.J.S. collected and analysed the data and wrote the manuscript; H.K. designed the study and treated patients; E.J., J.E.C, D.A.T, M.E.R., N.D., Y.A., M.K., P.K., W.G.W. and C.D.D. treated patients; C.B., D.M. and M.A.R. collected and analysed the data; F.R. designed the study, collected and analysed the data, treated patients and wrote the manuscript. All authors approved the final version of the manuscript.

Pharmacotherapeutical strategies in the prevention of acute, vaso-occlusive pain in sickle cell disease: a systematic review

Sickle-cell disease (SCD) is characterized by frequent and painful vaso-occlusive crises (VOCs). Various treatments have been evaluated over the years. However, a clear overview is lacking. The objective of this study was to systematically review all pharmacotherapeutical strategies in the prevention of VOCs beyond hydroxyurea. We performed a systematic literature search (MEDLINE, Embase, CENTRAL). Eligible studies were controlled clinical trials evaluating pharmacotherapeutical interventions targeting the reduction of VOCs in patients with SCD. Primary outcomes were the number or duration of SCD-related pain days, VOCs, or hospital admissions for VOCs. Secondary outcomes included time to first VOC or hospital admission for a VOC. A standardized data extraction sheet was used. The methodological quality of studies was assessed using Cochranes risk-of-bias tool. A total of 36 studies were included in this review, covering 26 different prophylactic interventions. The most promising interventions for reducing the frequency of either VOCs or hospitalizations were the oral antioxidants l-glutamine and ω-3 fatty acids and the IV antiadhesive agent crizanlizumab. Twenty-three studies did not show any beneficial effect of the intervention under investigation, and 6 studies were either too small or methodologically inadequate to draw conclusions. Because of the heterogeneity of interventions, no meta-analysis was performed. In conclusion, this review identified 3 promising pharmacotherapeutical strategies in the prevention of VOCs in SCD. Importantly, this study highlights the discrepancy between the significant burden of SCD worldwide and the low number of adequate trials performed. This review was registered at PROSPERO (CRD42015025250).

Dynamics of von Willebrand factor reactivity in sickle cell disease during vaso-occlusive crisis and steady state

Essentials The role of von Willebrand Factor (VWF) in the pathophysiology of sickle cell disease is unclear. We assessed markers of VWF during admission for vaso‐occlusive crisis (VOC) and steady state. VWF reactivity was higher during VOC and was associated with inflammation and neutrophil activation. Hyper‐adhesive VWF may promote VOC in sickle cell disease.

Inflammatory and endothelial markers during vaso-occlusive crisis and acute chest syndrome in sickle cell disease

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