Genetic studies of fetal hemoglobin in the Arab-Indian haplotype sickle cell-β(0) thalassemia

Diagnosis of Sickle Cell Disease and HBB Haplotyping in the Era of Personalized Medicine: Role of Next Generation Sequencing

Hemoglobin genotype and HBB haplotype are established genetic factors that modify the clinical phenotype in sickle cell disease (SCD). Current methods of establishing these two factors are cumbersome and/or prone to errors. The throughput capability of next generation sequencing (NGS) makes it ideal for simultaneous interrogation of the many genes of interest in SCD. This study was designed to confirm the diagnosis in patients with HbSS and Sβ-thalassemia, identify any ß-thal mutations and simultaneously determine the ß^S HBB haplotype. Illumina Ampliseq custom DNA panel was used to genotype the DNA samples. Haplotyping was based on the alleles on five haplotype-specific SNPs. The patients studied included 159 HbSS patients and 68 Sβ-thal patients, previously diagnosed using high performance liquid chromatography (HPLC). There was considerable discordance between HPLC and NGS results, giving a false +ve rate of 20.5% with a sensitivity of 79% for the identification of Sβthal. Arab/India haplotype was found in 81.5% of β^S chromosomes, while the two most common, of the 13 β-thal mutations detected, were IVS-1 del25 and IVS-II-1 (G>A). NGS is very versatile and can be deployed to simultaneously screen multiple gene loci for modifying polymorphisms, to afford personalized, evidence-based counselling and early intervention.

Prevalence and Diversity of Haplotypes of Sickle Cell Disease in the Eastern Province of Saudi Arabia

Hb F modulates sickle cell disease. Five major haplotypes of the β-globin gene cluster are associated with sickle cell disease. In the Eastern Province of Saudi Arabia, the Arab-Indian (AI) is most common. Single nucleotide polymorphism (SNP) genotyping (rs3834466, rs28440105, rs10128556, and rs968857) was carried out by nuclease allelic discrimination assay with target-specific forward and reverse primers, TaqMan probes, labeled with VIC and FAM. In 778 patients with sickle cell disease from the Eastern Province, a haplotype was assigned to 90.9% of all samples; 9.1% were classified as compound heterozygotes for the AI and an atypical haplotype. The distribution of haplotypes for 746 Hb S (HBB: c.20A > T) homozygotes was: 614 AI/AI, nine SEN/SEN (Senegal), 42 SEN/AI, nine CAM/CAM (Cameroon), one CAR (Central African Republic)/BEN (Benin), 71 AI/atypical. In Hb S/β-thalassemia (Hb S/β-thal), the distribution of Hb S haplotypes was: 22 AI/AI, one CAM/CAM, four AI/SEN, five AI/atypical. Mean Hb F in the haplotypes was: AI/AI 16.6 ± 7.5%, CAM/CAM 8.0 ± 4.1%, SEN/SEN 11.0 ± 5.1%, SEN/AI 15.1 ± 4.6%, AI/atypical 16.2 ± 6.5%. The presence of the SEN and CAM haplotypes was unexpected due to the apparent homogeneity of the population of the Eastern Province. We have successfully classified sickle cell disease haplotypes using the relatively inexpensive TaqMan assay for the first time. In addition, we have previously shown that children with AI haplotype have Hb F of 30.0% and mild disease, while in our cohort of adult AI patients, which might be the largest yet reported, Hb F was about 16.6%.

Sickle Cell Disease: Monitoring, Current Treatment, and Therapeutics Under Development

Screening and early detection of organ injury, as well as expanded use of red cell transfusion and hydroxyurea in children have changed best practices for clinical care in sickle cell disease. The current standard of care for children with sickle cell disease is discussed through a review of screening recommendations, disease monitoring, and approach to treatment. Novel pharmacologic agents under investigation in clinical trials are also reviewed.

2015 Clinical trials update in sickle cell anemia

Polymerization of HbS and cell sickling are the prime pathophysiological events in sickle cell disease (SCD). Over the last 30 years, a substantial understanding at the molecular level has been acquired on how a single amino acid change in the structure of the beta chain of hemoglobin leads to the explosive growth of the HbS polymer and the associated changes in red cell morphology. O2 tension and intracellular HbS concentration are the primary molecular drivers of this process, and are obvious targets for developing new therapies. However, polymerization and sickling are driving a complex network of associated cellular changes inside and outside of the erythrocyte, which become essential components of the inflammatory vasculopathy and result in a large range of potential acute and chronic organ damages. In these areas, a multitude of new targets for therapeutic developments have emerged, with several ongoing or planned new therapeutic interventions. This review outlines the key points of SCD pathophysiology as they relate to the development of new therapies, both at the pre-clinical and clinical levels.

Genomic approaches to identifying targets for treating β hemoglobinopathies

Sickle cell disease and β thalassemia are common severe diseases with little effective pathophysiologically-based treatment. Their phenotypic heterogeneity prompted genomic approaches to identify modifiers that ultimately might be exploited therapeutically. Fetal hemoglobin (HbF) is the major modulator of the phenotype of the β hemoglobinopathies. HbF inhibits deoxyHbS polymerization and in β thalassemia compensates for the reduction of HbA. The major success of genomics has been a better understanding the genetic regulation of HbF by identifying the major quantitative trait loci for this trait. If the targets identified can lead to means of increasing HbF to therapeutic levels in sufficient numbers of sickle or β-thalassemia erythrocytes, the pathophysiology of these diseases would be reversed. The availability of new target loci, high-throughput drug screening, and recent advances in genome editing provide the opportunity for new approaches to therapeutically increasing HbF production.