D. J. Weatherall

Inherited haemoglobin disorders: an increasing global health problem

Despite major advances in our understanding of the molecular pathology, pathophysiology, and control and management of the inherited disorders of haemoglobin, thousands of infants and children with these diseases are dying through lack of appropriate medical care. This problem will undoubtedly increase over the next 20 years because, as the result of a reduction in childhood mortality due to infection and malnutrition, more babies with haemoglobin disorders will survive to present for treatment. Although WHO and various voluntary agencies have tried to disseminate information about these diseases, they are rarely mentioned as being sufficiently important to be included in setting health care priorities for the future. It takes considerable time to establish expertise in developing programmes for the control and management of these conditions, and the lessons learned in developed countries will need to be transmitted to those countries in which they occur at a high frequency.

Phenotype-genotype relationships in monogenic disease: lessons from the thalassaemias

The remarkable phenotypic diversity of the β-thalassaemias reflects the heterogeneity of mutations at the β-globin locus, the action of many secondary and tertiary modifiers, and a wide range of environmental factors. It is likely that phenotype–genotype relationships will be equally complex in the case of many monogenic diseases. These findings highlight the problems that might be encountered in defining the relationship between the genome and the environment in multifactorial disorders, in which the degree of heritability might be relatively low and several environmental agents are involved. They also emphasize the value of an understanding of phenotype–genotype relationships in designing approaches to gene therapy.

The inherited diseases of hemoglobin are an emerging global health burden

It is estimated that in excess of 300,000 children are born each year with a severe inherited disorder of hemoglobin and that approximately 80% of these births occur in low- or middle-income countries. As these countries go through an epidemiologic transition, with a reduction in childhood and infant mortality due to improved public health measures, babies who would have previously died of these diseases before they were recognized are now surviving to present for diagnosis and treatment. Hence, they are presenting an increasing global health burden. Because of their uneven distribution in high-frequency populations, reflecting their complex population genetics, the true magnitude of this burden is still unknown. In many poor countries there are virtually no facilities for the diagnosis and management of these conditions, and even in richer countries there are limited data about their frequency, clinical course, or mortality. Without this information, it will be impossible to persuade governments about the increasing importance of these diseases. The situation will only be improved by concerted action on the part of the hematology community of the richer countries together with input from the major international health organizations and funding agencies.

K562 human leukaemic cells synthesise embryonic haemoglobin in response to haemin.

STUDIES of the regulation of human erythropoiesis and haemoglobin synthesis at different phases of development are hampered by the lack of a self-sustaining culture in which erythroid differentiation can be examined, and by difficulties in obtaining erythropoietic tissue in embryonic and early fetal life1. New insights into the regulation of murine erythropoiesis have been obtained by the study of established cultures of erythro-leukaemic cells (Friend cells) which can be induced to differentiate in vitro2. Recently, Andersson et al. 3,4 have reported that the K562 human cell line, obtained from a patient with an acute transformation of chronic myeloid leukaemia (CML) has properties in common with erythroid cells. In particular, cells of this line contain glycophorin and spectrin in their membranes and synthesise minute amounts of haemoglobin, detectable by radioimmunoassay. We have investigated the capacity of these cells to differentiate in vitro and report here that they are induced by haemin to synthesise large amounts of haemoglobin; preliminary analysis indicates that this is predominantly of the embryonic type.

A highly conserved amino-acid sequence in thrombospondin, properdin and in proteins from sporozoites and blood stages of a human malaria parasite

As a consequence of gene cloning and DNA sequencing several gene families are emerging in the field of cell–cell recognition. These include immunoglobulins, integrins, certain extracellular glycoproteins1 and a family of functionally unrelated proteins which include factor B2. We report here the cloning and sequencing of a gene from Plasmodium falciparum, coding for a protein we call thrombospondin related anonymous protein (TRAP), which shares certain sequence motifs common to other well-characterized proteins. The most significant homology is based around the sequence Trp-Ser-Pro-Cys-Ser-Val-Thr-Cys-Gly (WSPCSVTCG), present in three copies in region I of thrombospondin (TSP)3, six copies in properdin4 (P) and one copy in all the circumsporozoite (CS) proteins5–10 sequenced so far. TRAP also shares with certain extracellular glycoproteins, including TSP, the cell-recognition signal Arg-Gly-Asp (RGD)11, which has been shown to be crucial in the interaction of several extracellular glycoproteins with members of the integrin superfamily. Unlike the CS protein, TRAP is expressed during the erythrocytic stage of the parasite life cycle.

Rapid detection of alpha-thalassaemia deletions and alpha-globin gene triplication by multiplex polymerase chain reactions.

We describe a sensitive, reliable and reproducible method, based on three multiplex PCR assays, for the rapid detection of seven common α‐thalassaemia deletions and one α‐globin gene triplication. The new assay detects the α0 deletions – –SEA, – (α)20.5, – –MED, – –FIL and – –THAI in the first multiplex PCR, the second multiplex detects the –α3.7 deletion and αααanti3.7 variant, the third multiplex detects the –α4.2 deletion. This simple multiplex method should greatly facilitate the genetic screening and molecular diagnosis of these determinants in populations where α‐thalassaemias are prevalent.

Global epidemiology of sickle haemoglobin in neonates: a contemporary geostatistical model-based map and population estimates

Summary Background Reliable estimates of populations affected by diseases are necessary to guide efficient allocation of public health resources. Sickle haemoglobin (HbS) is the most common and clinically significant haemoglobin structural variant, but no contemporary estimates exist of the global populations affected. Moreover, the precision of available national estimates of heterozygous (AS) and homozygous (SS) neonates is unknown. We aimed to provide evidence-based estimates at various scales, with uncertainty measures. Methods Using a database of sickle haemoglobin surveys, we created a contemporary global map of HbS allele frequency distribution within a Bayesian geostatistical model. The pairing of this map with demographic data enabled calculation of global, regional, and national estimates of the annual number of AS and SS neonates. Subnational estimates were also calculated in data-rich areas. Findings Our map shows subnational spatial heterogeneities and high allele frequencies across most of sub-Saharan Africa, the Middle East, and India, as well as gene flow following migrations to western Europe and the eastern coast of the Americas. Accounting for local heterogeneities and demographic factors, we estimated that the global number of neonates affected by HbS in 2010 included 5 476 000 (IQR 5 291 000–5 679 000) AS neonates and 312 000 (294 000–330 000) SS neonates. These global estimates are higher than previous conservative estimates. Important differences predicted at the national level are discussed. Interpretation HbS will have an increasing effect on public health systems. Our estimates can help countries and the international community gauge the need for appropriate diagnoses and genetic counselling to reduce the number of neonates affected. Similar mapping and modelling methods could be used for other inherited disorders. Funding The Wellcome Trust.

The interaction of alpha-thalassemia and homozygous sickle-cell disease.

Patients with homozygous sickle-cell disease may be homozygous for alpha-thalassemia 2 (alpha-/alpha-), may be heterozygous for alpha-thalassemia 2 (alpha-/alpha alpha), or may have a normal alpha-globin-gene complement (alpha alpha/alpha alpha). We compared the clinical and hematologic features of 44 patients who had sickle-cell disease and homozygous alpha-thalassemia 2 with those of controls with the two hematologic conditions. The patients with homozygous alpha-thalassemia 2 had significantly higher red-cell counts and levels of hemoglobin and hemoglobin A2, as well as significantly lower hemoglobin F, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, mean corpuscular volume, reticulocyte counts, irreversibly-sickled cell counts, and serum total bilirubin levels, than those with a normal alpha-globin-gene complement. Heterozygotes (alpha-/alpha alpha) had intermediate values. In the group with homozygous alpha-thalassemia 2, fewer patients had episodes of acute chest syndrome and chronic leg ulceration and more patients had splenomegaly, as compared with patients in other two subgroups. These data confirm previous suggestions that alpha-thalassemia inhibits in vivo sickling in homozygous sickle-cell disease and may be an important genetic determinant of its hematologic severity.

FIRST-TRIMESTER FETAL DIAGNOSIS FOR HAEMOGLOBINOPATHIES: THREE CASES

Abstract By means of a simplified method for trophoblast biopsy together with restriction endonuclease analysis of fetal DNA, first-trimester diagnoses were successfully made in two fetuses at risk for homozygous β thalassaemia and in one at risk for sickle cell anaemia.

Negative epistasis between the malaria-protective effects of α + -thalassemia and the sickle cell trait

The hemoglobinopathies, disorders of hemoglobin structure and production, protect against death from malaria. In sub-Saharan Africa, two such conditions occur at particularly high frequencies: presence of the structural variant hemoglobin S and α+-thalassemia, a condition characterized by reduced production of the normal α-globin component of hemoglobin. Individually, each is protective against severe Plasmodium falciparum malaria, but little is known about their malaria-protective effects when inherited in combination. We investigated this question by studying a population on the coast of Kenya and found that the protection afforded by each condition inherited alone was lost when the two conditions were inherited together, to such a degree that the incidence of both uncomplicated and severe P. falciparum malaria was close to baseline in children heterozygous with respect to the mutation underlying the hemoglobin S variant and homozygous with respect to the mutation underlying α+-thalassemia. Negative epistasis could explain the failure of α+-thalassemia to reach fixation in any population in sub-Saharan Africa.