Screening and genetic diagnosis of haemoglobin disorders

Hematological abnormalities in patients with distal renal tubular acidosis and hemoglobinopathies

Mutations of the human SLC4A1 gene encoding erythroid and kidney isoforms of anion exchanger 1 (AE1, band 3) result in erythrocyte abnormalities or distal renal tubular acidosis (dRTA) and such mutations are observed in Southeast Asia, where hemoglobinopathies are prevalent. Genetic and hematological studies in 18 Thai patients with dRTA have shown that 12 of them (67%) carried SLC4A1 mutations (7 G701D/G701D, 3 SAO/G701D, and 2 G701D/A858D). Of these 12 patients, three had homozygous G701D/G701D and heterozygous Hb E; one compound heterozygous SAO/G701D and heterozygous alpha(+)-thalassemia; and one compound heterozygous G701D/A858D and heterozygous Hb E. Of 6 patients without SLC4A1 mutation, two each carried heterozygous or homozygous Hb E and one of the latter also had Hb H disease (--(SEA)/-alpha(4.2)). The blood smears of patients with homozygous G701D/G701D showed approximately 25% ovalocytes. Strikingly, the patients with coexistence of homozygous G701D/G701D and heterozygous Hb E had 58% ovalocytes. Similarly, the patients who had compound heterozygous SAO/G701D showed 49% ovalocytes, but the patient with coexistence of compound heterozygous SAO/G701D and heterozygous alpha(+)-thalassemia had 70% ovalocytes. Our previous study has shown that under metabolic acidosis, the patients with homozygous G701D/G701D or compound heterozygous SAO/G701D had reticulocytosis, indicating compensated hemolysis. A patient with compound heterozygous SAO/G701D and heterozygous alpha(+)-thalassemia presented with hemolytic anemia and hepatosplenomegaly which was alleviated by alkaline therapy. Taken together, the coexistence of both homozygous or compound heterozygous SLC4A1 mutations and hemoglobinopathy has a combined effect on red cell morphology and degree of hemolytic anemia, which is aggravated by acidosis.

Hemoglobinopathies in the Sudan

In a prospective study, we evaluated hematological parameters in freshly obtained venous blood samples from 632 Sudanese patients attending the outpatient department at Khartoum Teaching Hospital, Khartoum, Sudan, in the period between March and July 2005. The patients were surveyed for full blood count (FBC) and hemoglobin (Hb) electrophoresis using a cellulose acetate method. Hb S [beta6(A3)Glu-->Val] was the most common abnormal Hb, which was not unexpected because the subjects live in the center of a malaria-affected area. The study showed low hematological parameters due to various causes including poor nutrition as well as infections and hemolytic processes.

Fetal Hemoglobin Inducers from the Natural World: A Novel Approach for Identification of Drugs for the Treatment of {beta}-Thalassemia and Sickle-Cell Anemia

The objective of this review is to present examples of lead compounds identified from biological material (fungi, plant extracts and agro-industry material) and of possible interest in the field of a pharmacological approach to the therapy of beta-thalassemia using molecules able to stimulate production of fetal hemoglobin (HbF) in adults. Concerning the employment of HbF inducers as potential drugs for pharmacological treatment of beta-thalassemia, the following conclusions can be reached: (i) this therapeutic approach is reasonable, on the basis of the clinical parameters exhibited by hereditary persistence of fetal hemoglobin patients, (ii) clinical trials (even if still limited) employing HbF inducers were effective in ameliorating the symptoms of beta-thalassemia patients, (iii) good correlation of in vivo and in vitro results of HbF synthesis and gamma-globin mRNA accumulation indicates that in vitro testing might be predictive of in vivo responses and (iv) combined use of different inducers might be useful to maximize HbF, both in vitro and in vivo. In this review, we present three examples of HbF inducers from the natural world: (i) angelicin and linear psoralens, contained in plant extracts from Angelica arcangelica and Aegle marmelos, (ii) resveratrol, a polyphenol found in grapes and several plant extracts and (iii) rapamycin, isolated from Streptomyces hygroscopicus.

Use of multiplex PCR and CE for gene dosage quantification and its biomedical applications for SMN, PMP22, and alpha-globin genes

Many genetic diseases are caused by the presence of point mutations, small insertions, and deletions in respective genes, and the number of diseases known to be caused by deletions and duplications involving large DNA genomes is increasing. These changes lead to underexpression or overexpression of the gene, according to changes in gene dosage. The methods for the detection of point mutations, small insertions, and deletions are well established, but the detection of larger genomic deletions or duplications is more difficult. Due to the lack of efficient and technically feasible protocols for gene dosage quantification, we describe a diagnostic protocol employing a combination of available methods. The efficient and accurate gene dosage quantification platform is combined with multiplex PCR and CE, and applied to detect dosages of several genes, including SMN, PMP22, and alpha-globin genes. The reliability of this novel methodology shows that it is a relatively speedy and low-cost procedure and a significant tool for genetic diagnosis. Its sensitivity and specificity for identifying deletion and duplication genotypes approach 100%. Moreover, once we establish this powerful system, we will further apply this technique to the rapid detection of trisomy syndromes and microdeletion syndromes, including trisomy 13, Down syndrome, DiGeorge syndrome, and others.

A double heterozygote for (deltabeta)0-thalassemia and codons 41/42 (-TTCT) behaves as a homozygote for the frameshift mutation in a Chinese family

We present the case of a child in whom beta-thalassemia (thal) major was apparently caused by homozygosity for a 4-base deletion mutation [codons 41/42 (-TTCT)] of the beta-globin gene. However, the mutation was not identified in the father. The presence of a deletional beta-thal was detected by long-range polymerase chain reaction (PCR). We emphasize that the mutations found in the patient should always be confirmed to be present in both parents before molecular analysis is employed for clinical purposes.

High-Throughput Microtiter Well-Based Chemiluminometric Genotyping of 15 HBB Gene Mutations in a Dry-Reagent Format

Background: Hemoglobinopathies are the most common inherited diseases worldwide. Various methods for genotyping of hemoglobin, beta (HBB) gene mutations have been reported, but there is need for a high sample-throughput, cost-effective method for simultaneous screening of several mutations. We report a method that combines the high detectability and dynamic range of chemiluminescence with the high allele-discrimination ability of probe extension reactions for simultaneous genotyping of 15 HBB mutations in a high sample-throughput, dry-reagent format.

Methods: We genotyped the HBB mutations IVSI-110G>A, CD39C>T, IVSI-1G>A, IVSI-6T>C, IVSII-745C>G, IVSII-1G>A, FSC6GAG>G-G, −101C>T, FSC5CCT>C−, IVSI-5G>A, FSC8AAG>−G, −87C>G, IVSII-848C>A, term+6C>G, and HbS (cd6GAG>GTG). The method used comprises the following: (a) duplex PCR that produces fragments encompassing all 15 mutations, (b) probe extension reactions in the presence of fluorescein-modified dCTP, using unpurified amplicons, and (c) microtiter well-based assay of extension products with a peroxidase-antifluorescein conjugate and a chemiluminogenic substrate. We used lyophilized dry reagents to simplify the procedure and assigned the genotype by the signal ratio of the normal-to-mutant–specific probe.

Results: We standardized the method by analyzing 60 samples with known genotypes and then validated by blindly genotyping 115 samples with 45 genotypes. The results were fully concordant with sequencing. The reproducibility (including PCR, probe extension reaction, and chemiluminometric assay) was studied for 20 days, and the CVs were 11%–19%.

Conclusions: This method is accurate, reproducible, and cost-effective in terms of equipment and reagents. The application of the method is simple, rapid, and robust. The microtiter well format allows genotyping of a large number of samples in parallel for several mutations.

Complex phenotypes in the haemoglobinopathies: recommendations on screening and DNA testing

This document considers a number of scenarios involving complex haemoglobinopathies and provides 28 recommendations at both the clinical and laboratory levels on how these should be managed.

Inherited hemoglobin disorders in Guinea-Bissau, West Africa: a population study

The determination of the prevalence of inherited hemoglobin (Hb) disorders in endemic areas is important in order to develop programs for their control and management. The aim of this study is to determine the prevalence of inherited Hb diseases in Guinea-Bissau which is situated on the west coast of Africa, between Senegal and Guinea. One thousand and fifty-seven blood samples were collected and analyzed with high performance liquid chromatography (HPLC) for detection of beta-thalassemia (thal) and Hb variants, and by gap polymerase chain reaction (gap-PCR) for the detection of deletions in the alpha-globin genes. We found 4.7% children were heterozygous for Hb S [beta6(A3)Glu-->Val, GAG -->GTG], 0.2% were homozygous for Hb S, and 0.3% were heterozygous for Hb C [beta6(A3)Glu-->Lys, GAG -->AAG]. One child had heterozygous beta+-thal, 13.8% were heterozygous for the -alpha3.7 deletion, 1.5% were homozygous for the -alpha3.7 deletion, and 1.5% were heterozygous for the -alpha4.2 deletion. We recommend national screening programs to focus primarily on sickle cell disease, since beta-thal is rare, and the observed alpha-thal deletions are of minor genetic importance.

Development of severe anemia during fever episodes in patients with hemoglobin E trait and hemoglobin H disease combinations

Globin chain imbalance and tissue hypoxia are important determinants of the clinical severity of thalassemias. Phenotypic expression may be further modified by interactions between alpha- and beta-thalassemia defects. We retrospectively and prospectively studied the clinical and hematologic features in children and adults with hemoglobin (Hb) E trait/Hb H disease (SEA/Paksé) (seven cases) and Hb E trait/Hb H disease (SEA/Constant Spring) (29 cases) and found that they had similar presentations. The severity of these two intermediate thalassemic manifestations ranged from very mild to severe. Severe anemia developed in accordance with very high fever, whereupon the range of Hb and hematocrit (Hct) levels declined to 5.2-5.8 g/dL and 13%-19%, respectively. In one case, during a hemoconcentrated state as occurs in dengue hemorrhagic fever, the Hb and Hct were 10 g/dL and 31%; the latter rose to 35% after fluid therapy. In some patients, the range of Hb and Hct levels was constantly low (4.3-5.8 g/dL and 15%-19%, respectively). (If dengue hemorrhagic fever is misdiagnosed, a fatal outcome may occur for thalassemic patients.) After a hemodiluted condition as in acute post-streptococcal glomerulonephritis, the respective Hb and Hct were 5.4 g/dL and 19%. These observations suggest that the instability of Hb E, especially during fever, may play an important role in the clinical manifestations of Hb E trait/Hb H disease with Hb Paksé and with Hb Constant Spring.

α-Thalassemia: Hb H Disease and Hb Barts Hydrops Fetalis

alpha-Thalassemia mutations are one of the most common mutations of man, and they cause Hb H disease and Hb Barts hydrops fetalis. Hb H disease is not necessarily a benign disorder as has been generally thought. Furthermore, in southern China and in Southeast Asia, there are 2-3 times more fetuses afflicted with the invariably fatal Hb Barts hydrops fetalis than with the beta-thalassemia major or intermedia. These findings underscore the public health importance of these hereditary disorders, and they call for better education, diagnosis, treatment, prevention, and research for these diseases.

How to interpret and pursue an abnormal complete blood cell count in adults

A complete blood cell count (CBC) is one of the most common laboratory tests in medicine. For example, at our institution alone, approximately 1800 CBCs are ordered every day, and 10% to 20% of results are reported as abnormal. Therefore, it is in every clinician's interest to have some understanding of the specific test basics as well as a structured action plan when confronted with abnormal CBC results. In this article, we provide practical diagnostic algorithms that address frequently encountered conditions associated with CBC abnormalities including anemia, thrombocytopenia, leukopenia, polycythemia, thrombocytosis, and leukocytosis. The objective is to help the nonhematologist recognize when a subspecialty consultation is reasonable and when it may be circumvented, thus allowing a cost-effective and intellectually rewarding practice.

Genetic Evaluation and Counseling of Couples with Recurrent Miscarriage: Recommendations of the National Society of Genetic Counselors

The objective of this document is to provide recommendations for genetic evaluation and counseling of couples with recurrent miscarriage (RM). The recommendations are the opinions of the multidisciplinary Inherited Pregnancy Loss Working Group (IPLWG), with expertise in genetic counseling, medical genetics, maternal fetal medicine, internal medicine, infectious disease, cytogenetics, and coagulation disorders. The IPLWG defines RM as three or more clinically recognized consecutive or non-consecutive pregnancy losses occurring prior to fetal viability (<24 weeks gestation). These recommendations are provided to assist genetic counselors and other health care providers in clinical decision-making, as well as to promote consistency of patient care, guide the allocation of medical resources, and increase awareness of the psychosocial and cultural issues experienced by couples with RM. The IPLWG was convened with support from the March of Dimes Western Washington State Chapter and the University of Washington Division of Medical Genetics. The recommendations are U.S. Preventive Task Force Class III, and are based on clinical experiences, review of pertinent English-language published articles, and reports of expert committees. This document reviews the suspected causes of RM, provides indications for genetic evaluation and testing, addresses psychosocial and cultural considerations, and provides professional and patient resources. These recommendations should not be construed as dictating an exclusive course of medical management, nor does the use of such recommendations guarantee a particular outcome. The professional judgment of a health care provider, familiar with the circumstances of a specific case, should always supersede these recommendations.

Thalassaemia screening in pregnancy

PURPOSE OF REVIEW

This review provide an update on antenatal screening and diagnosis of thalassaemia disorders.

RECENT FINDINGS

The topics covered are the effectiveness of antenatal screening programmes for thalassaemia, its prenatal diagnosis, molecular basis and laboratory findings, ultrasound screening for haemoglobin Bart's disease, and non-invasive prenatal diagnosis of thalassaemia.

SUMMARY

Universal antenatal screening for thalassaemia carriers should be implemented in populations with a high prevalence of this condition. The appropriate measure to screen for alpha and beta thalassaemias remains mean cell haemoglobin (<27 pg) or mean corpuscular volume (<80 fl). A haemoglobin pattern and iron profile should follow if the red cell indices are low. In a population where alpha thalassaemia is prevalent, it is advisable to check the partner's mean cell haemoglobin or mean corpuscular volume as well. Further cascades of investigations will depend on these results and the prevalence of other haemoglobinopathies in that population. Invasive prenatal diagnosis remains the gold standard for diagnosis in high-risk couples. Provided expertise is available, ultrasound measurement of the cardiothoracic ratio appears a good screening tool for alpha thalassaemia major. Non-invasive prenatal diagnosis by identification of a paternal mutation in maternal plasma, although currently at the experimental stage, may be an option in the future.

Analytical evaluation of the Tosoh HLC-723 G7 automated HPLC analyzer for hemoglobin A2 and F determination

OBJECTIVES

The analytical performance of a new automated HPLC system (Tosoh HLV-723 G7) for Hb A(2) and Hb F quantification in blood was studied.

DESIGN AND METHODS

Hb A(2) and Hb F measurements were studied for imprecision, linearity, carry-over, interferences and sample concentration effect. Method comparison study was performed with the Bio-Rad Variant II HPLC system. Hb F results were also compared with those obtained by the alkaline denaturation test. The detection of some common Hb variants was also studied.

RESULTS

Hb A(2) within-run and between-run CVs were found between 0.8-2.2% and 2.9-7.2%, respectively, while CVs for Hb F were up to 10.0% in normal and between 1.9-5.3% at more clinically relevant Hb F concentrations (>1.5%). Comparison study with Bio-Rad Variant II for Hb A(2) determination showed good correlation but highlighted calibration differences. The following results were obtained in two different laboratories: y = 1.163x - 0.52, r = 0.9918, n = 144 (Lab A); y = 1.060x - 0.40, r = 0.9920, n = 93 (Lab B). With regard to the determination of Hb F, the measurements performed by the tested method was found to correlate well with the alkaline denaturation test (y = 1.0138x - 0.36, r = 0.9842, n = 20) and with the Variant II HPLC system (y = 0.812x + 0.52, r = 0.9835, n = 110). An excellent linearity (r = 0.999) was found for both Hb A(2) and Hb F in the range 0.8-19%. Hb S, Hb C and Hb D can be presumptively identified by the assigned retention time windows.

CONCLUSION

The new analyzer Tosoh HLV-723 G7 was found to be a reliable method for Hb A(2) and Hb F quantification and for the presumptive identification of some common Hb variants.

Molecular diagnosis of inherited disorders: lessons from hemoglobinopathies

Hemoglobinopathies constitute a major health problem worldwide, with a high carrier frequency, particularly in certain regions where malaria has been endemic. These disorders are characterized by a vast clinical and hematological phenotypic heterogeneity. Over 1,200 different genetic alterations that affect the DNA sequence of the human alpha-like (HBZ, HBA2, HBA1, and HBQ1) and beta-like (HBE1, HBG2, HBG1, HBD, and HBB) globin genes are mainly responsible for the observed clinical heterogeneity. These mutations, together with detailed information about the resulting phenotype, are documented in the globin locus-specific HbVar database. Family studies and comprehensive hematological analyses provide useful insights for accurately diagnosing thalassemia at the DNA level. For this purpose, numerous techniques can provide accurate, rapid, and cost-effective identification of the underlying genetic defect in affected individuals. The aim of this article is to review the diverse methodological and technical platforms available for the molecular diagnosis of inherited disorders, using thalassemia and hemoglobinopathies as a model. This article also attempts to shed light on issues closely related to thalassemia diagnostics, such as prenatal and preimplantation genetic diagnoses and genetic counseling, for better-quality disease management.

Molecular diagnosis of haemoglobin disorders

The haemoglobinopathies refer to a diverse group of inherited disorders characterized by a reduced synthesis of one or more globin chains (thalassaemias) or the synthesis of a structurally abnormal haemoglobin (Hb). In prevalent regions, the thalassaemias often coexist with a variety of structural Hb variants giving rise to complex genotypes and an extremely wide spectrum of clinical and haematological phenotypes. An appreciation of these phenotypes is needed to facilitate the definitive diagnosis of the causative mutations to inform management and counselling. Haematological and biochemical investigations, and family studies provide essential clues to the different interactions and are fundamental to DNA diagnostics of the Hb disorders. With the exception of a few rare deletions and rearrangements, the molecular lesions causing haemoglobinopathies are all identifiable by PCR-based techniques. Although a full spectrum of >1000 mutations causing haemoglobinopathies has been documented, in practice only a limited number are associated with disease states and clinical significance. Furthermore, each at-risk ethnic group has its own combination of common Hb variants and thalassaemia mutations. Prior identification of the ethnic origin is thus an important part of the diagnostic strategy which becomes less reliable in the UK because of the large ethnic mix. Although the current approach using a combination of different PCR-based techniques seems to work in most laboratories, practice pressures with the imminent implementation of universal antenatal screening for clinically significant Hb disorders in the UK will require a higher throughput approach for DNA diagnostics in the near future. The complex mutational spectrum and the compactness of the globin genes places them in an ideal position for the different non-gel based analytical platforms.

A Community Profile of Alpha Thalassaemia in Western Australia

OBJECTIVE

To investigate the current prevalence of alpha-thalassaemia in the population of Western Australia, which has received substantial immigration from South-East Asia during the last 30 years.

METHOD

Over a 1-year period commencing July 2002, alpha-thalassaemia DNA testing was performed on 920 blood samples received from the Migrant Health Service, referring doctors or pathology laboratories in Western Australia. Molecular testing for alpha-thalassaemia was performed on extracted DNA for single and double alpha-globin gene deletions and mutations by PCR.

RESULTS

An alpha-globin gene abnormality was detected in 35.4% (326/920) of samples. There were 177 cases (50.6%) with a single gene deletion alpha(+)-thalassaemia, most commonly -3.7 kb, and 102 cases (31.2%) with double alpha-gene deletions (alpha(0)-thalassaemia), including 7 cases of HbH disease.

CONCLUSION

Overall, the findings amount to 1.7 new cases of alpha-thalassaemia per 10,000 population in the 12-month period and demonstrate that alpha-thalassaemia is an increasingly common disorder in the Western Australian population. This has important implications for community outreach programmes, genetic counselling and the screening of at-risk populations.

Anemia in adults: a contemporary approach to diagnosis

There are numerous ways of classifying the causes of anemia, and no one way is necessarily superior to another. It is equally important to appreciate the differences in the approaches to diagnosis between children and adults, men and women, and persons of different ethnic backgrounds. Regardless of the specific algorithm followed in evaluating anemia, it is essential that easily remediable causes such as nutritional deficiencies, hemolysis, and anemia of renal insufficiency are identified early and treated appropriately. In general, the differential diagnosis of anemia can be substantially narrowed by subcategorization into "microcytic," "normocytic," and "macrocytic" subtypes on the basis of mean corpuscular volume. However, such classification is a starting point and not infallible. Each category then can be deciphered using a stepwise approach that utilizes readily accessible laboratory tests.

Diagnóstico da hemoglobina S: análise comparativa do teste de solubilidade com a eletroforese em pH alcalino e ácido no período neonatal

OBJETIVOS: avaliar a eficácia do teste de solubilidade como método de triagem na detecção de Hb S no período neonatal, comparando-o com as técnicas de eletroforese em pH alcalino e ácido. MÉTODOS: o sangue de cordão umbilical de 1.988 recém-nascidos (RN) na maternidade do Instituto Materno-Infantil de Pernambuco (IMIP), durante o período outubro de 1996 a março de 1997, foi submetido à eletroforese de hemoglobina em pH alcalino e ao teste de solubilidade. A eletroforese de hemoglobina em pH ácido foi realizada como teste confirmatório em todos os casos em que a eletroforese em pH alcalino foi positiva para Hb S ou Hb C. RESULTADOS: a eletroforese de Hb em pH alcalino detectou a presença de Hb S em 105 (5,3%) amostras. A análise dessas 105 amostras através da eletroforese em pH ácido mostrou que 98 (93,3%) mantiveram o mesmo padrão eletroforético. O teste de solubilidade detectou apenas um RN portador de Hb S. CONCLUSÕES: a eletroforese de Hb em pH alcalino mostrou-se eficaz no diagnóstico da hemoglobina S no período neonatal, podendo ser utilizada nos locais onde técnicas mais sofisticadas não estão implantadas. O teste de solubilidade não serve como abordagem diagnóstica para a presença de Hb S no período neonatal.