Alpha thalassaemia in Zambian newborn

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.

Anaemia in pregnant Ghanaian women: importance of malaria, iron deficiency, and haemoglobinopathies

In sub-Saharan Africa, anaemia in pregnancy results from multiple causes including malaria, iron deficiency and haemoglobinopathies. In a cross-sectional study among 530 pregnant women in Ghana in November-December 1998, red blood cell indices were analysed with respect to malaria, serum concentrations of ferritin and C-reactive protein (CRP), and the haemoglobin and alpha-globin genotypes. Anaemia (haemoglobin [Hb] < 11 g/dL) was found in 54% of the women; 63% harboured malaria parasites at predominantly low numbers. Ferritin levels were considerably influenced by malaria and inflammatory processes (CRP > 0.6 mg/dL). Depending on the definition applied, the prevalence of iron deficiency ranged between 5% and 46%. The HbAS trait was observed in 14%, HbAC and elevated HbF in 7% each, and sickle cell disease in 1%. Heterozygous beta-thalassaemia was present in 1% of the women and alpha(+)-thalassaemia in 33% (29% heterozygous, 4% homozygous). Women with HbAS had higher malaria parasite densities than those with HbAA. In individuals with highly elevated HbF (> 10%), parasitaemia occurred in 27% only. Low gravidity, second trimester of pregnancy, malaria, raised CRP levels, and homozygous alpha(+)-thalassaemia were independent risk factors for anaemia in multivariate analysis. alpha(+)-Thalassaemia, however, was associated with a lesser degree of malarial anaemia when compared to non-thalassaemic women. Iron deficiency appears not to be a major health problem in this population. Haemoglobinopathies are common but, except for homozygous alpha(+)-thalassaemia, do not substantially contribute to anaemia in pregnancy. alpha(+)-Thalassaemia ameliorates malarial anaemia in pregnant women.

The population genetics of the haemoglobinopathies

The haemoglobinopathies are the commonest single-gene disorders known, almost certainly because of the protection they provide against malaria, as attested by a number of observations. The geographical distributions of malaria and haemoglobinopathies largely overlap, and microepidemiological surveys confirm the close relationship between them. For two of the commonest disorders, haemoglobin S and alpha(+)-thalassaemia, there is also good clinical evidence for protection against malaria morbidity. However, not all the evidence appears to support this view. In some parts of the world malaria and haemoglobinopathies are not, and never have been, coexistent. It is also difficult to explain why the majority of haemoglobinopathies appear to be recent mutations and are regionally specific. Here we argue that these apparent inconsistencies in the malaria hypothesis are the result of processes such as genetic drift and migration and of demographic changes that have occurred during the past 10,000 years. When these factors are taken into account, selection by malaria remains the force responsible for the prevalence of the haemoglobinopathies.

A prospective study of the influence of alpha thalassaemia on morbidity from malaria and immune responses to defined Plasmodium falciparum antigens in Gambian children

The protective effect of alpha thalassaemia (-alpha/alpha alpha) against morbidity from falciparum malaria was assessed in a prospective study of rural Gambian children. The gene frequency for single alpha-globin gene deletions was 0.12. Malariometric indices measured during cross-sectional surveys and morbidity from malaria determined by weekly surveillance were similar in children with alpha thalassaemia and in those with a normal alpha-globin genotype. However, the small number of children who carried both alpha thalassaemia and the sickle cell trait had fewer clinical episodes of malaria than children with the sickle cell trait alone. Specific antibody responses and cell-mediated immune responses in vitro to defined Plasmodium falciparum antigens were measured in children participating in the study. In general, there was no evidence of an increased prevalence or intensity of humoral or cell-mediated immune responses to the malaria antigens studied in children heterozygous for alpha thalassaemia compared with children with a normal alpha-globin genotype.

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.