alpha-Thalassemia among sickle cell anemia patients in various African populations

Alpha thalassemia among sickle cell anaemia patients in Kampala, Uganda

BACKGROUND

Sickle cell anaemia is prevalent in sub Saharan Africa. While α+-thalassaemia is known to modulate sickle cell anaemia, its magnitude and significance in Uganda have hitherto not been described.

OBJECTIVES

To determine the prevalence of α+thalassaemia among sickle cell anaemia patients in Mulago Hospital and to describe the clinical and laboratory findings in these patients.

METHODS

A cross sectional study was carried out on patients with sickle cell anaemia in Kampala. Dried blood spots were used to analyze for the deletional α+ thalassaemia using multiplex polymerase chain reaction.

RESULTS

Of the 142 patients with sickle cell anaemia, 110 (77.5%) had the αα+thalassaemia deletion. The gene frequency of (-α) was 0.425. Ninety one percent (100/110) of those with α+thalassaemia were heterozygous (αα/α-). Amongst the patients older than 60 months, 15 (83.3%) of those without αα+thalassaemia had significant hepatomegaly of greater than 4 cm compared to 36 (45.6%) of those with α+thalassaemia (p=0.003).

CONCLUSION

The gene frequency of (-α) of 0.425 noted in this study is higher than that reported from many places in Africa. Concurrent alpha thalassemia might be a protective trait against significant hepatomegaly in sickle cell anaemia patients more than 60 months of age at Mulago hospital.

Differences in the clinical and genotypic presentation of sickle cell disease around the world

Sickle cell disease (SCD), caused by a mutation in the β-globin gene HBB, is widely distributed in malaria endemic regions. Cardiopulmonary complications are major causes of morbidity and mortality. Hemoglobin SS (Hb SS) represents a large proportion of SCD in the Americas, United Kingdom, and certain regions of Africa while higher proportions of hemoglobin SC are observed in Burkina Faso and hemoglobin Sβ-thalassemia in Greece and India. Coinheritance of α-thalassemia and persistence of hemoglobin F production are observed in highest frequency in certain regions of India and the Middle East. As confirmed in the PUSH and Walk-PHaSST studies, Hb SS, absence of co-inheriting alpha-thalassemia, and low hemoglobin F levels tend to be associated with more hemolysis, lower hemoglobin oxygen saturations, greater proportions of elevated tricuspid regurgitant jet velocity and brain natriuretic peptide, and increased left ventricular mass index. Identification of additional genetic modifiers will improve prediction of cardiopulmonary complications in SCD.

Sickle cell disease in Middle East Arab countries

The sickle cell (HbS) gene occurs at a variable frequency in the Middle Eastern Arab countries, with characteristic distribution patterns and representing an overall picture of blood genetic disorders in the region. The origin of the gene has been debated, but studies using β-globin gene haplotypes have ascertained that there were multiple origins for HbS. In some regions the HbS gene is common and exhibits polymorphism, while the reverse is true in others. A common causative factor for the high prevalence and maintenance of HbS and thalassaemia genes is malaria endemicity. The HbS gene also co-exists with other haemoglobin variants and thalassaemia genes and the resulting clinical state is referred to as sickle cell disease (SCD). In the Middle Eastern Arab countries, the clinical picture of SCD expresses two distinct forms, the benign and the severe forms, which are related to two distinct β-globin gene haplotypes. These are referred to as the Saudi-Indian and the Benin haplotypes, respectively. In a majority of the Middle Eastern Arab countries the HbS is linked to the Saudi-Indian haplotype, while in others it is linked to the Benin haplotype. This review outlines the frequency, distribution, clinical feature, management and prevention as well as gene interactions of the HbS genes with other haemoglobin disorders in the Middle Eastern Arab countries.

Evidence that microdeletions in the alpha globin gene protect against the development of sickle cell glomerulopathy in humans

There is a large variability in the severity of the clinical manifestations of sickle cell anemia (SSA), including renal involvement. Haplotypes in the beta-globin gene cluster associated with the geographical origin of the sickle mutation, as well as microdeletions in the alpha-globin genes, could provide an epigenetic influence on the heterogeneous outcome in SSA. It has been determined that the cause of progressive renal insufficiency in SSA is a glomerulopathy, clinically detected by the presence of macroalbuminuria (albumin excretion rate >300 mg/g creatinine). To investigate the role of the alpha-globin gene microdeletion and beta-globin gene cluster haplotypes on the degree of glomerular involvement, 76 adult SSA patients (hemoglobin SS) were studied to determine the relationship between these genetic markers and the development of sickle cell glomerulopathy. Macroalbuminuria was present in 22 (29%) of 76 adult SSA patients. The coinheritance of microdeletions in one or two of the four alpha-globin genes (alpha-thalassemia) was associated with a lower prevalence of macroalbuminuria (13%) versus patients with intact alpha-globin genes (40%, P = 0.01). By contrast, there was no association between albuminuria and beta-globin gene haplotypes (Central African Republic [CAR] versus non-CAR haplotypes). Patients with alpha-globin gene microdeletions had lower mean corpuscular volumes and mean corpuscular hemoglobin concentration than patients with all four alpha genes (86+/-2 versus 99+/-3 fl, and 33.9+/-0.2 versus 34.9+/-0.2%, respectively, P<0.05). There were no such hematologic differences between CAR and non-CAR beta-globin haplotypes. There were no differences in duration of disease (age), hemoglobin levels, reticulocyte index, and lactate dehydrogenase levels between those with and without glomerulopathy, but the mean arterial pressure was higher (87+/-1 mm Hg) in patients with intact alpha gene locus versus those with microdeletions (80+/-2 mm Hg, P<0.05). It is concluded that the coinheritance of microdeletions in the alpha-globin gene locus in SSA patients confers "renoprotection" by mechanisms not related to the degree of anemia or the severity of hemolysis, but could be related to a reduced mean corpuscular volume or to a lower erythrocyte hemoglobin concentration.

Genetic and hematological studies in a group of 114 adult patients with SC sickle cell disease

The clinical and biological heterogeneity of sickle cell hemoglobin (Hb) C disease (SC disease) is similar to sickle cell anemia, but has a much milder course. The effect of genetic factors such as alpha thalassemia or beta-globin gene haplotype has been analyzed in a limited number of cases. In this work, we report about 114 adult SC patients, aged 15 to 65 years (M/F = 0.93). The frequency of deletional alpha thalassemia (alpha(-3.7)) was found to be about 35%. The coinheritance of an alpha-thalassemia trait with SC disease had no effect on the hemoglobin level but hemolysis was significantly reduced. In these patients, as described for homozygous Hb S individuals, the Hb F level was higher in females than in males and in individuals carrying the beta(s)-Senegal haplotype. This haplotype involves the presence of an Xmnl site 5' to Ggamma, which is considered responsible for an increased Ggamma/Agamma ratio. Our survey showed that some genetic factors may modulate hematological parameters in SC disease.

Effect of alpha-thalassemia and beta-globin gene cluster haplotypes on the hematological and clinical features of sickle-cell anemia in Brazil

To compare the features of sickle-cell anemia in Brazil with those in other locales, we studied the effects of the beta-globin-like gene cluster haplotype and alpha-thalassemia upon the clinical and hematological features in 85 patients. The distribution of haplotypes differed from that in the United States and Jamaica. The Central African Republic (CAR) haplotype predominated; 34% of patients were CAR haplotype homozygotes, 45% CAR/Benin homozygotes, and 11% Benin homozygotes. No Senegal haplotype chromosomes were observed. Alpha-thalassemia was present in 17.5% of patients. HbF levels were higher in Benin homozygotes, compared with the other two groups (P < 0.05). Nearly half the patients with a CAR haplotype had leg ulcers, compared to 12.5% of the Benin homozygote group; stroke did not occur in alpha-thalassemia carriers, but neither result was statistically significant. As in other studies, our results indicate that the CAR haplotype may be associated with more severe disease.

Molecular epidemiology of the thalassaemias (including haemoglobin E)

The thalassaemias are the most common genetic disorders of man, and over the last decade the molecular epidemiology of these defects has been studied in detail. After briefly reviewing the great diversity of mutations giving rise to these conditions, four global regions are discussed in more detail. The thalassaemias, of which haemoglobin E is one, are most frequent in Asia, where recent work has defined the molecular basis of the beta thalassaemias and the frequencies of the various types of alpha + and alpha 0 thalassaemia. Oceanic populations have a range of globin gene variants remarkably different to those of south-east Asia. Most is known about the nature and frequencies of thalassaemia mutations in Mediterranean countries, where prenatal diagnosis programmes have been very successful in reducing the frequency of new cases of thalassaemia major. alpha + Thalassaemia is the most common haemoglobinopathy in sub-Saharan Africa, and molecular studies of American Blacks with beta thalassaemia have elucidated the probable molecular basis of the mild form of this disorder in Africans. Although each geographical region has its own group of common beta thalassaemia mutations, with little overlap, most of these appear to have had a single origin. The question of single or multiple origins for HbE in south-east Asia is unresolved. Recombination events producing alpha + thalassaemia deletions are frequent, whereas alpha 0 thalassaemia is produced by a variety of large deletions, each of which has had a single origin. The evidence favouring natural selection by P. falciparum malaria as the primary cause of high frequencies of the thalassaemias throughout the tropics and subtropics is reviewed. While the mechanism of protection remains unclear, epidemiological evidence supporting the hypothesis is strong, but more information is required from case-control studies on the amount of protection provided by the various thalassaemia genotypes.

Alpha thalassaemia in Zambian newborn

The umbilical cord blood from 109 consecutive Zambian neonates (excluding those found to be anti-HIV positive) were analysed for haemoglobin (Hb) Bart's and for alpha thalassaemia by restriction endonuclease analysis. This showed that 52.3% had the genotype alpha alpha/alpha alpha, 38.5% had -alpha 3.7/alpha alpha, 7.3% had -alpha 3.7/-alpha 3.7 and 1.8% had alpha alpha alpha/alpha alpha. The alpha thalassaemia gene (-alpha) frequency was 0.27. There were no apparent differences in gene frequency between six major Zambian ethnic groups. Detection of Hb Bart's identified all alpha-thalassaemia homozygotes (-alpha/-alpha), but fewer than 10% of heterozygotes (-alpha/alpha alpha). alpha-thalassaemia was associated with slight but significant anaemia and microcytosis.

Analysis of crossover type in the alpha -3.7 haplotype among sickle cell anemia patients from various parts of Africa

The frequency of alpha+-thalassemia has been determined in African populations carrying beta S-chromosomes of different origins. All these alpha+ thalassemias result from a right-ward deletion. Restriction mapping of the alpha -3.7/haplotype with the enzyme ApaI only showed the presence of a type I crossover. RsaI polymorphism at the 5' end of Z alpha 2 is largely represented in the normal population (gene frequency 23%) but, in our series, never associated with the alpha -3.7/haplotype.

Alpha-thalassaemia in Nigeria: its interaction with sickle-cell disease

We have determined the molecular basis and frequency of alpha-thalassaemia in Nigeria. The alpha-thalassaemia determinant in this population is caused by only one type of single alpha globin gene deletion (-alpha 3.7). Comparison of the haematological features of those patients who have sickle-cell disease with (-alpha/alpha alpha, -alpha/-alpha) or without (alpha alpha/alpha alpha) alpha-thalassaemia showed similar trends to those reported in Jamaican and U.S. patients with these interactions. However, in contrast to studies in some other African populations we have shown that the frequency of alpha-thalassaemia in Nigeria is the same (0.24) in patients with or without homozygous sickle-cell disease (AA, AS and AC genotypes).