Polymorphisms in the heme oxygenase-1 and bone morphogenetic protein receptor type 1b genes and estimated glomerular filtration rate in Brazilian sickle cell anemia patients

Involvement of haptoglobin in disease development

Haptoglobin (HP) is a liver glycoprotein that is actively synthesized during inflammatory and hemolytic processes. It also has pro-oxidant and proinflammatory properties, which are a function of its genotype. The genetic polymorphism of the chains leads to synthesis of three phenotypes/proteins, which are related to the number and type of chains and their molecular weight, namely HP1-1, HP1-2 and HP2-2. Patients with HP2-2 have more vascular complications, while those with HP1-1 have fewer. HP is involved in the worsening of diseases, such as HP2-2 in aggravation of vaso-occlusive crises in sickle cell disease, and worsening of the pathophysiology of other diseases. In contrast, HP1-1 confers better protection against diseases. All of this suggests that further studies should be conducted, including experimental and analytical studies focused on demonstrating the influence of different HP genotypes on individual clinical and hematological data. This would help in understanding the role played by this genetic polymorphism in the pathophysiology of diseases.

Systematic Review of Genetic Modifiers Associated with the Development and/or Progression of Nephropathy in Patients with Sickle Cell Disease

Sickle cell nephropathy (SCN) is a common complication of sickle cell disease (SCD) that significantly contributes to morbidity and mortality. In addition to clinical and life-style factors, genetic variants influence this risk. We performed a systematic review, searching five databases. Studies evaluating the effect of genetic modifiers on SCN were eligible. Twenty-eight studies (fair-to-good quality) were included: one genome-wide association study, twenty-six case-control studies, and one article combining both approaches. APOL1 was significantly associated with albuminuria and hyperfiltration in children and with worse glomerular filtration in adults. On the other hand, alpha-thalassemia protected patients against albuminuria and hyperfiltration, while BCL11A variants were protective against albuminuria alone. The HMOX1 long GT-tandem repeat polymorphism led to a lower glomerular filtration rate. No modifiers for the risk of hyposthenuria were identified. A genome-wide association approach identified three new loci for proteinuria (CRYL1, VWF, and ADAMTS7) and nine loci were linked with eGFR (PKD1L2, TOR2A, CUBN, AGGF1, CYP4B1, CD163, LRP1B, linc02288, and FPGT-TNNI3K/TNNI3K). In conclusion, this systematic review supports the role of genetic modifiers in influencing the risk and progression of SCN. Incorporating and expanding this knowledge is crucial to improving the management and clinical outcomes of patients at risk.

Sickle Cell Disease and CKD: An Update

BACKGROUND

Sickle cell disease is an inherited red blood cell disorder that affects approximately 100,000 people in the USA and 25 million people worldwide. Vaso-occlusion and chronic hemolysis lead to dysfunction of vital organ systems, with the kidneys being among the most commonly affected organs.

SUMMARY

Early renal manifestations include medullary ischemia with the loss of urine-concentrating ability and hyperfiltration. This can be followed by progressive damage characterized by persistent albuminuria and a decline in the estimated glomerular filtration rate. The risk of sickle nephropathy is greater in those with the APOL1 G1 and G2 kidney risk variants and variants in HMOX1 and lower in those that coinherit α-thalassemia. Therapies to treat sickle cell disease-related kidney damage focus on sickle cell disease-modifying therapies (e.g., hydroxyurea) or those adopted from the nonsickle cell disease kidney literature (e.g., renin-angiotensin-aldosterone system inhibitors), although data on their clinical efficacy are limited to small studies with short follow-up periods. Kidney transplantation for end-stage kidney disease improves survival compared to hemodialysis but is underutilized in this patient population.

KEY MESSAGES

Kidney disease is a major contributor to early mortality, and more research is needed to understand the pathophysiology and develop targeted therapies to improve kidney health in 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.

An overview of pathophysiology and treatment options of osteonecrosis of femoral head in sickle cell disease

Osteonecrosis of the femoral head (ONFH) is the most prevalent musculoskeletal pathologic manifestation of sickle cell disease (SCD) resulting in an osteonecrotic event. This review aimed to summarize mechanisms involved in pathophysiology of ONFH and treatment options available in Saudi Arabia to treat SCD patients with complication of osteonecrotic event. The pathophysiology of ONFH include genetic and micro particles involvement. The progression of osteonecrosis involves reduced levels of bioactive compounds in peripheral blood mononuclear cells and elevated CD4+T circulating levels to stimulate pro-inflammatory cytokines contributing to inflammation at target site. Initial treatment approach is pharmacological agents use to mitigate risk. Further, bone morphogenetic protein stimulation initiate bone formation and treatment can be improved with the use of bone morphogenetic protein, total hip arthroplasty and cell therapies. This review provides baseline information for future studies to be carried out in Saudi Arabia to improve treatment options in SCD patients with ONFH.

Significance of heme oxygenase-1(HMOX1) gene on fetal hemoglobin induction in sickle cell anemia patients

Though the patients with sickle cell anemia (SCA) inherit same genetic mutation, they show considerable phenotypic heterogeneity. It has been observed that patients with elevated fetal hemoglobin (HbF) levels have a relatively mild clinical course. There is sparse literature on the association of higher HbF levels leading to reduction in the oxidative stress in SCA patients. Hence in this study, the significance between the HMOX1 gene polymorphisms and the HbF levels has been studied. Preliminary screening was carried out. Genotyping of 3 variants in the HMOX1 gene was performed in 90 SCA patients and 50 healthy controls by PCR–RFLP, GeneScan and direct DNA sequencing. It was observed that SCA patients with higher HbF levels, showed improved hematological indices with an inverse effect on HbS levels. The TT genotype of rs2071746 (A→T) polymorphism was found to be associated with elevated HbF levels (P: 0.012). Also, the long form (> 25 GT repeats) of rs3074372 (GT)n repeats was found to be linked with increased HbF levels. We could not find any association of rs2071749 (A→G) polymorphism with the HbF levels. As, the sickle cell anemia patients show significant oxidative stress due to hemolysis, the study of polymorphisms in the HMOX1 gene may act as a potential independent marker for elevated HbF levels.