HLA class II haplotypes distinctly associated with vaso-occlusion in children with sickle cell disease

Genetic Variation and Sickle Cell Disease Severity: A Systematic Review and Meta-Analysis

Importance

Sickle cell disease (SCD) is a monogenic disorder, yet clinical outcomes are influenced by additional genetic factors. Despite decades of research, the genetics of SCD remain poorly understood.

Objective

To assess all reported genetic modifiers of SCD, evaluate the design of associated studies, and provide guidelines for future analyses according to modern genetic study recommendations.

Data Sources

PubMed, Web of Science, and Scopus were searched through May 16, 2023, identifying 5290 publications.

Study Selection

At least 2 reviewers identified 571 original, peer-reviewed English-language publications reporting genetic modifiers of human SCD phenotypes, wherein the outcome was not treatment response, and the comparison was not between SCD subtypes or including healthy controls.

Data Extraction and Synthesis

Data relevant to all genetic modifiers of SCD were extracted, evaluated, and presented following STREGA and PRISMA guidelines. Weighted z score meta-analyses and pathway analyses were conducted.

Main Outcomes and Measures

Outcomes were aggregated into 25 categories, grouped as acute complications, chronic conditions, hematologic parameters or biomarkers, and general or mixed measures of SCD severity.

Results

The 571 included studies reported on 29 670 unique individuals (50% ≤ 18 years of age) from 43 countries. Of the 17 757 extracted results (4890 significant) in 1552 genes, 3675 results met the study criteria for meta-analysis: reported phenotype and genotype, association size and direction, variability measure, sample size, and statistical test. Only 173 results for 62 associations could be cross-study combined. The remaining associations could not be aggregated because they were only reported once or methods (eg, study design, reporting practice) and genotype or phenotype definitions were insufficiently harmonized. Gene variants regulating fetal hemoglobin and α-thalassemia (important markers for SCD severity) were frequently identified: 19 single-nucleotide variants in BCL11A, HBS1L-MYB, and HBG2 were significantly associated with fetal hemoglobin (absolute value of Z = 4.00 to 20.66; P = 8.63 × 10-95 to 6.19 × 10-5), and α-thalassemia deletions were significantly associated with increased hemoglobin level and reduced risk of albuminuria, abnormal transcranial Doppler velocity, and stroke (absolute value of Z = 3.43 to 5.16; P = 2.42 × 10-7 to 6.00 × 10-4). However, other associations remain unconfirmed. Pathway analyses of significant genes highlighted the importance of cellular adhesion, inflammation, oxidative and toxic stress, and blood vessel regulation in SCD (23 of the top 25 Gene Ontology pathways involve these processes) and suggested future research areas.

Conclusions and Relevance

The findings of this comprehensive systematic review and meta-analysis of all published genetic modifiers of SCD indicated that implementation of standardized phenotypes, statistical methods, and reporting practices should accelerate discovery and validation of genetic modifiers and development of clinically actionable genetic profiles.

Blockade of endothelin-1 receptor B regulates molecules of the major histocompatibility complex in sickle cell disease

Major Histocompatibility Complex (MHC) molecules have been proposed to play a role in Sickle Cell Disease (SCD) pathophysiology. Endothelial cells express MHC molecules following exposure to cytokines. SCD is characterized, in part, by vascular endothelial cell activation, increased oxidative stress, sickle cell adhesion, and excess levels of endothelin-1 (ET-1) contributing to vaso-occlusive crises. ET-1 activates endothelial cells, induces oxidative stress and inflammation, and alters erythrocyte volume homeostasis. However, the role of ET-1 on MHC regulation in SCD is unclear. We first studied two sickle transgenic knockout mouse models of moderate to severe disease phenotype, βS-Antilles and Berkeley (BERK) mice. We observed significant increases in H2-Aa mRNA levels in spleens, lungs, and kidneys from transgenic sickle mice when compared to transgenic knockout mice expressing human hemoglobin A (HbA). Mice treated for 14 days with ET-1 receptor antagonists significantly reduced H2-Aa mRNA levels. We characterized the effect of ET-1 on MHC class II expression in the human endothelial cell line EA.hy926. We observed dose-dependent increases in the expression of MHC class II (HLA-DRA) and MHC transcription factor (CIITA) that were significantly blocked by treatment with BQ788, a selective blocker of ET-1 type B receptors. Chromatin immunoprecipitation studies in EA.hy926 cells showed that ET-1 increased Histone H3 acetylation of the HLA-DRA promoter, an event blocked by BQ788 treatment. These results implicate ET-1 as a novel regulator of MHC class II molecules and suggest that ET-1 receptor blockade represents a promising therapeutic approach to regulate both immune and vascular responses in SCD.

Prolonged QTc Interval in Nigerian Children with Sickle Cell Anemia

Prolonged QTc interval, a risk factor for ventricular arrhythmia, occurs in sickle cell anemia. The aim of this study was to determine the risk of prolonged QTc interval and its relationship with vaso-occlusive painful crises (VOCs) and follow-up steady-state in the same children with sickle cell anemia. This prospective cohort study enrolled 38 subjects, aged 5-17 years. History of bone pain and examination were obtained during VOC and steady-state. Assessment of QTc interval was with 12-lead electrocardiography. The QTc interval value >0.440 seconds was taken as prolonged. Median (interquartile range) of QTc interval was higher during VOC [0.447 (0.438-0.459) seconds] than during steady-state [0.435 (0.417-0.440) seconds]. Risk of prolonged QTc interval was higher during VOC (68.4%) than in steady-state (21.1%) with relative risk of 3.250 [95% confidence interval (CI) = 1.692-6.241]. Prolonged QTc interval was likely to occur [area under curve (AUC) = 0.759, p<0.001] during VOC with 68.4% sensitivity, 78.9% specificity and at cutoff point of 0.441 seconds. Prolonged QTc interval negatively correlated with packed cell volume (PCV) during VOC [r_s (36) = -0.14, p = 0.387]. Binary logistics of the combined effect of PCV and gender on QTc interval showed that during VOC, males were more likely to have prolonged QTc [odds ratio (OR): 1.337 (95% CI: 0.327-5.464; p = 0.686]. Children with sickle cell anemia, particularly males, were three-times more likely to have prolonged QTc interval during VOC when QTc interval was >0.441 seconds. Routine electrocardiography may help to identify those with QTc intervals above this threshold for prompt cardiac-oriented management.

Myocardial injury in patients with sickle cell anaemia and myocardial ischaemia in Calabar, Nigeria

Background In children with sickle cell anaemia (SCA), ischaemic electrocardiogram (ECG) changes occur during both vaso-occlusive crises (VOC) and the steady state. Myocardial ischaemia evidenced by an ischaemic pattern on ECG may lead to myocardial injury which is evidenced by elevated serum cardiac troponin T (cTnT). Occasionally, the myocardial injury is fatal. Aim To determine the relationship between raised serum cTnT levels and an ischaemic ECG pattern in children with SCA. Methods This was a dual study design comprising a prospective cohort study of a group of children with SCA observed during VOC and 6 weeks later during follow-up steady state, and a case-control study of SCA children and apparently healthy children. The subjects were 34 SCA children aged 5-17 years and 34 age- and sex-matched apparently healthy controls with haemoglobin genotype AA attending University of Calabar Teaching Hospital. VOC was diagnosed by clinical examination and a history of bone pain. During VOC and follow-up steady state, an ECG was performed and blood taken for serum cTnT estimation. In the apparently healthy children, only serum cTnT was estimated. Serum cTnT was analysed by electrochemiluminescence immune-assay. Ischaemic ECG was assessed using the World Heart Federation criteria. Results Twenty-eight (82.4%) SCA children had elevated serum cTnT during VOC and it was elevated in only six (17.6%) of them during the steady state. An ischaemic ECG was observed in 25 (73.5%) and 20 (58.8%) of them during VOC and the steady state, respectively. Ischaemic ECG identified SCA children with elevated cTnT during VOC (sensitivity 75%, specificity 33.3%) and the follow-up steady state (sensitivity 50%, specificity 39.3%). Measures of agreement between ECG and cTnT in detecting myocardial injury were poor during VOC (κ 0.07, p = 0.68) and the follow-up steady state (κ - 0.06, p = 0.63). Conclusions Most SCA children have an ischaemic ECG with elevated serum cTnT, especially during VOC, which suggests ischaemic-induced cardiac injury. However, elevated serum cTnT can occur without an ischaemic ECG and vice versa. Performing only electrocardiography or cTnT to detect ischaemia-induced cardiac injury may be misleading. Therefore, when there is a high index of suspicion, both tests should be undertaken, especially during VOC, to ensure prompt, effective treatment. Abbreviations AHC, apparently healthy children; AUC, area under the ROC curve; BMI, body mass index; cTnT, cardiac troponin T; ECG, electrocardiogram; EDTA, ethylene diamine tetra-acetic acid; GFR, glomerular filtration rate; HbS, haemoglobin S; HLA, human leucocyte antigen; LVH, left ventricular hypertrophy; ROC, receiver operating characteristic; SCA, sickle cell anaemia; UCTH, University of Calabar Teaching Hospital; URL, upper reference limit; USFDA, United States Food and Drug Administration; USNIH, United States National Institutes of Health; VOC, vaso-occlusive painful crisis; WHF, World Heart Federation.