Hemoglobin Jamaica plain--a sickling hemoglobin with reduced oxygen affinity

IVS-II-16 (G>C) (HBB: c.315+16G>C) or IVS-II-666 (C>T) (HBB: c.316-185C>T) Mutations Trigger an Hb S (HBB: c.20A>T)/β+-Thalassemia Phenotype in an Hb S Trait Patient

Sickle cell trait is a medical condition caused by the presence of both mutant Hb S (HBB: c.20A>T) and normal Hb A alleles. Although sickle cell trait is typically considered to be asymptomatic and benign, genetic modifiers and mutations can lead to severe clinical complications. In this study, the possible pathogenicity of the IVS-II-16 (G>C) (HBB: c.315+16G>C) and IVS-II-666 (C>T) (HBB: c.316-185C>T) mutations, which are considered to be neutral polymorphisms, and the association between the Hb S mutation are presented. To the best of our knowledge, these polymorphisms have not been previously reported in any sickle cell trait patient, and no relevant studies have been conducted. We recently studied a 40-year-old woman (proband), diagnosed to be an Hb S/β-thalassemia (β-thal) carrier. β-Globin mutations were analyzed using a DNA sequencer based on the Sanger method. The HbVar and ClinVar databases show IVS-II-16 and IVS-II-666 to be intronic mutations. However, statements in these data banks contradict our findings. In the present study, a transfusion-dependent Hb S patient, behaving as an Hb S/β-thal case due to these mutations, was reported. These mutations have not been previously reported in an Hb S patient. Although the IVS-II-16 and IVS-II-666 mutations were previously reported as benign, they converted the Hb S phenotype to transfusion-dependent Hb S/β-thal when combined with Hb S. In this regard, IVS-II-16 and IVS-II-666 mutations may not be innocent, as previously thought.

Non-S Sickling Hemoglobin Variants: Historical, Genetic, Diagnostic, and Clinical Perspectives

Apart from hemoglobin-S (HbS), there are other Hb variants (non-S sickling Hb variants) that cause sickle cell disease. However, the profiles of these non-S sickling Hb variants have neither been collated nor harmonized. A literature search revealed 14 non-S sickling Hb variants (HbC-Harlem, HbC-Ziguinchor, HbS-Travis, HbS-Antilles, HbS-Providence, HbS-Oman, HbS-Cameroon, HbS-South End, Hb Jamaica Plain, HbC-Ndjamena, HbS-Clichy, HbS-San Martin, HbS-Wake, and HbS-São Paulo). Generally, the non-S sickling Hb variants are double mutants with the HbS mutation (GAG>GTG: βGlu6Val) and additional β-chain mutations. Consequently, non-S sickling Hb variants give positive solubility and sickling tests, but they differ from HbS with respect to stability, oxygen affinity, and electro-chromatographic characteristics. Similarities and discrepancies between HbS and non-S sickling Hb variants create diagnostic pitfalls that can only be resolved by elaborate electro-chromatographic and/or genetic tests. It is therefore imperative that tropical hematologists should have a thorough understanding of these atypical sickling Hb variants. Collated and harmonized appraisal of the non-S sickling Hb variants have not been previously undertaken. Hence, this paper aims to provide a comprehensive but concise historical, genetic, comparative, diagnostic, and clinical overview of non-S sickling Hb variants. The elaborate techniques often required for precise diagnosis of non-S sickling Hb variants are regrettably not readily available in low resource tropical countries, which paradoxically carry the heaviest burden of sickling disorders. We strongly recommend that tropical countries should upgrade their diagnostic laboratory facilities to avoid misdiagnosis of these atypical Hb mutants.

Genetic Basis and Genetic Modifiers of β-Thalassemia and Sickle Cell Disease

β-thalassemia and sickle cell disease (SCD) are prototypical Mendelian single gene disorders, both caused by mutations affecting the adult β-globin gene. Despite the apparent genetic simplicity, both disorders display a remarkable spectrum of phenotypic severity and share two major genetic modifiers-α-globin genotype and innate ability to produce fetal hemoglobin (HbF, α₂γ₂).This article provides an overview of the genetic basis for SCD and β-thalassemia, and genetic modifiers identified through phenotype correlation studies. Identification of the genetic variants modifying HbF production in combination with α-globin genotype provide some prediction of disease severity for β-thalassemia and SCD but generation of a personalized genetic risk score to inform prognosis and guide management requires a larger panel of genetic modifiers yet to be discovered.Nonetheless, genetic studies have been successful in characterizing some of the key variants and pathways involved in HbF regulation, providing new therapeutic targets for HbF reactivation.

A combinatorial F box protein directed pathway controls TRAF adaptor stability to regulate inflammation

Uncontrolled activation of tumor necrosis factor receptor-associated factor (TRAF) proteins may result in profound tissue injury by linking surface signals to cytokine release. Here we show that a ubiquitin E3 ligase component, Fbxo3, potently stimulates cytokine secretion from human inflammatory cells by destabilizing a sentinel TRAF inhibitor, Fbxl2. Fbxo3 and TRAF protein in circulation positively correlated with cytokine responses in septic subjects and we furthermore identified a hypofunctional Fbxo3 human polymorphism. A small molecule inhibitor targeting Fbxo3 was sufficient to lessen severity of cytokine-driven inflammation in several murine disease models. These studies identify a pathway of innate immunity that may characterize subjects with altered immune responses during critical illness or provide a basis for therapeutic intervention targeting TRAF protein abundance.

Hemoglobin variants: biochemical properties and clinical correlates

Diseases affecting hemoglobin synthesis and function are extremely common worldwide. More than 1000 naturally occurring human hemoglobin variants with single amino acid substitutions throughout the molecule have been discovered, mainly through their clinical and/or laboratory manifestations. These variants alter hemoglobin structure and biochemical properties with physiological effects ranging from insignificant to severe. Studies of these mutations in patients and in the laboratory have produced a wealth of information on hemoglobin biochemistry and biology with significant implications for hematology practice. More generally, landmark studies of hemoglobin performed over the past 60 years have established important paradigms for the disciplines of structural biology, genetics, biochemistry, and medicine. Here we review the major classes of hemoglobin variants, emphasizing general concepts and illustrative examples.

Pitfalls in the genetic diagnosis of Hb S

Patients homozygous for Hb S need to be properly identified to start as early as possible a treatment that should avoid complications. For prevention and genetic counseling, carriers of Hb S have to be screened. Hb S is easily detected by several analytical systems, but other variants, usually harmless, may behave as Hb S, leading to false positive diagnosis. Some interactions may also cause difficulties in the qualitative or quantitative interpretation of a chromatography or electrophoresis profile. These problems may result from several causes among which the simultaneous presence of an α chain variant leading to the formation of tetramers having both an α and a β chain modified, the presence of a second mutation within the Hb S allele, the existence of a compound heterozygous state leading to some "Hb S trait with dominantly transmitted sickle cell disease (SCD)", and the presence of thalassemic allele affecting the intracellular proportion of Hb S. In case of any "dominant Hb S trait" a thorough Hb study is always required. This work reports some of the difficulties observed by us, or reported in the literature, and propose how to avoid them and reach a correct diagnosis.

Hb S-São Paulo: a new sickling hemoglobin with stable polymers and decreased oxygen affinity

Hb S-São Paulo (SP) [HBB:c.20A>T p.Glu6Val; c.196A>G p.Lys65Glu] is a new double-mutant hemoglobin that was found in heterozygosis in an 18-month-old Brazilian male with moderate anemia. It behaves like Hb S in acid electrophoresis, isoelectric focusing and solubility testing but shows different behavior in alkaline electrophoresis, cation-exchange HPLC and RP-HPLC. The variant is slightly unstable, showed reduced oxygen affinity and also appeared to form polymers more stable than the Hb S. Molecular dynamics simulation suggests that the polymerization is favored by interfacial electrostatic interactions. This provides a plausible explanation for some of the reported experimental observations.

Sickle-cell disease

Sickle-cell disease is one of the most common severe monogenic disorders in the world. Haemoglobin polymerisation, leading to erythrocyte rigidity and vaso-occlusion, is central to the pathophysiology of this disease, although the importance of chronic anaemia, haemolysis, and vasculopathy has been established. Clinical management is basic and few treatments have a robust evidence base. One of the main problems of sickle-cell disease in children is the development of cerebrovascular disease and cognitive impairment, and the role of blood transfusion and hydroxycarbamide for prevention of these complications is starting to be understood. Recurrent episodes of vaso-occlusion and inflammation result in progressive damage to most organs, including the brain, kidneys, lungs, bones, and cardiovascular system, which becomes apparent with increasing age. Most people with sickle-cell disease live in Africa, where little is known about this disease; however, we do know that the disorder follows a more severe clinical course in Africa than for the rest of the world and that infectious diseases have a role in causing this increased severity of sickle-cell disease. More work is needed to develop effective treatments that specifically target pathophysiological changes and clinical complications of sickle-cell disease.

Strategy for identification by mass spectrometry of a new human hemoglobin variant with two mutations in Cis in the beta-globin chain: Hb S-Clichy [beta6(A3)Glu-->Val; beta8(A5)Lys-->Thr]

Hemoglobinopathies are the most frequent genetic diseases in the world. Among them, the Hb S variant [beta6(A3)Glu-->Val], which, in the homozygous state, produces a severe disease known as sickle cell anemia with polymerization of Hb S inside red blood cells under hypoxic conditions. Additional mutations, in cis or in trans of the beta(S)-globin chain, may inhibit or enhance the polymerization process. We describe here a new hemoglobin (Hb) variant (Hb S-Clichy) which carries the beta(S)-globin chain and an additional mutation beta8(A5)Lys-->Thr. The variant was detected by routine electrophoretic techniques and cation exchange liquid chromatography (CE-LC). Globin chain separation by reversed phase LC (RP-LC) showed normal and abnormal beta chains, confirming that the additional abnormality was located in cis to Hb S. Electrospray ionization mass spectrometry (ESI-MS) gave a 57 Da mass decrease for the abnormal globin chain. The abnormal chain was isolated and submitted to trypsin digestion. Normal peptides betaT-1 and betaT-2 were not observed on the matrix-assisted laser desorption-time of flight (MALDI-TOF) mass spectrum but a new peptide betaT-1,2 was detected. Nano LC-ESI-MS/MS of the new peptide showed that the glutamic acid at codon 6 was replaced by a valine residue, and the lysine at codon 8 was replaced by a threonine residue, as confirmed by DNA sequencing. This example demonstrates that in a population where Hb S is present, every unidentified Hb needs to be clearly characterized to prevent major sickle cell syndromes. In addition, the identification of these variants must be considered in newborn screening for sickle cell disease, using either classical biochemical methods or MS techniques.

Sickle cell disease in a carrier with pyruvate kinase deficiency

We report a case of sickle cell disease (SCD) in a patient who is a carrier for the sickle mutation with no additional mutations in the beta globin genes. Sequencing of the PK-LR genes showed that she was also heterozygous for the L272V mutation in exon 7, which is known to cause pyruvate kinase (PK) deficiency. It appeared that sickling in the heterozygous state is related to decreased oxygen affinity associated with PK deficiency in this unusual case.

Social Ecology, Genomics, and African American Health: A Nonlinear Dynamical Perspective

This article offers a model that clarifies the degree of interdependence between social ecology and genomic processes. Drawing on principles from nonlinear dynamics, the model delineates major lines of bifurcation involving people's habitat, their family health history, and collective catastrophes experienced by their community. It shows how mechanisms of resource acquisition, depletion, and preservation can lead to disruptions in basic metabolism and in the activity of cytokines, neurotransmitters, and protein kinases, thus giving impetus to epigenetic changes. The hypotheses generated from the model are discussed throughout the article for their relevance to health problems among African Americans. Where appropriate, they are examined in light of data from the National Vital Statistics System. Multiple health outcomes are considered. For any one of them, the model makes clear the unique and converging contributions of multiple antecedent factors.

Sickle cell disease caused by Hb S/Québec-CHORI: treatment with hydroxyurea and response

Sickle hemoglobin (Hb S;betaGlu 6 Val) is due to an A>T transversion in codon 6 of the beta-globin gene. Other variant hemoglobins mimic Hb A, S, or C on newborn screening and clinical laboratory diagnostic tools, thus making their correct identification potentially difficult. Sickling disorders can result in individuals who are compound heterozygous for beta-globin mutations (e.g., Hb SC, HbSO(Arab)). The authors report a second case of HbS/Québec-CHORI, a severe compound heterozygous sickling disorder and their experience managing this patient with hydroxyurea.

Heterozygosity for a Mendelian disorder as a risk factor for complex disease

While genetic diseases are generally classified as being either 'simple' monogenic or 'complex' polygenic, the distinction between Mendelian and complex disorders is becoming increasingly blurred. Mendelian disorders may demonstrate qualities more typical of multifactorial diseases through shared clinical presentations, the effect of genetic modifiers, moonlighting proteins, synergistic heterozygosity, disease manifestations in heterozygotes and situations where heterozygosity for a 'simple' disorder proves to be a risk factor for seemingly unrelated complex diseases. A recent example of the last instance is the observation that mutations in glucocerebrosidase, the enzyme deficient in Gaucher disease, may be a risk factor for the development of Parkinson disease and other synucleinopathies. Insights gleaned from the study of Mendelian disorders may ultimately lead to a better understanding of factors influencing complex diseases.

Hemoglobin Loves Park [beta68 (E12) Leu-->Phe]: report of five cases including one originating from a de novo mutation

Hemoglobin (Hb) Loves Park [beta68 (E12) Leu-->Phe] was identified in a 2-year-old Portuguese boy with anemia, microcytosis, and hypochromia. This Hb variant was detected by isoelectric focusing and quantified by reverse-phase high-performance liquid chromatography (HPLC) (48.4%), and the DNA mutation was identified by HBB (beta-globin gene) sequencing. Hematological and biochemical analyses performed on his parents revealed normal hematological parameters and normal hemoglobin and globin chain profiles. DNA sequence analysis of the HBB gene of both parents showed the absence of the Hb Loves Park mutation. Study of the haplotypes in the beta-globin gene cluster confirmed parenthood. Moreover, paternity was confirmed by the study of nine short tandem repeats (STRs) and four variable-number tandem repeat (VNTRs) loci. The most likely explanation for these results is that the Hb Loves Park mutation has occurred de novo in this family. The original American cases of Hb Loves Park, from a family of Italian origin, which were never published, as well as two additional cases, are also included in this report. Functional studies revealed that Hb Loves Park is stable and has a decreased oxygen affinity.

A novel sickle hemoglobin: hemoglobin S-south end

Sickle hemoglobin (Hb S; beta Glu6Val) is due to an A<T transversion in codon 6 of the beta-globin gene. Several Hb S variants have both the Hb S mutation plus another mutation in the same beta-globin gene. Some of these variant hemoglobins can lead to sickle cell disease even in the simple heterozygote. Moreover, some variant hemoglobins mimic Hb A, S, or C on one or several clinical laboratory diagnostic tools, thus making their correct identification potentially problematic. The authors report a novel Hb S variant hemoglobin, Hb S-South End (beta Glu6Val, GAG>GTG; beta Lys132Asn, AAA>AAC). When present alone, the beta Lys132Asn mutation has low oxygen affinity. Therefore, this mutation may enhance the polymerization of the Hb S variant. Furthermore, the variant hemoglobin mimics Hb A on high-pressure liquid chromatography, and its identity is not easily diagnosed. A succinct review of variant sickle hemoglobins is also presented.