In 1949, British scientist John Burdon Sanderson Haldane made a novel connection between red cell disorders and malaria: The genetic mutations that lead to several types of anemias, including thalassemia and sickle cell anemia, have persisted in certain human populations where malaria was historically endemic because individuals heterozygous for these mutations have some type of advantage against the bloodborne infectious disease.1
Red cell disorders and malaria, Haldane observed, were prevalent among people living in warm climates of European, North African, and West Asian countries that surround the Mediterranean Sea (collectively called the Mediterranean Basin).
"Haldane was working on anemias in the Mediterranean in the 1940s, but he didn't know for sure that these were thalassemias at the time," Thomas N. Williams, FMedSci, professor in the department of medicine at the Imperial College and St. Mary’s Hospital in London, told ASH Clinical News. Dr. Williams conducts research on hematologic disorders, including on mechanisms of malaria resistance in children with red cell disorders at the KEMRI-Wellcome Trust Research Programme in Kilifi, Kenya.
"The molecular biology of thalassemia had not yet been worked out. That happened only about 20 years later," he continued. "Dr. Haldane knew that this was an inherited disorder only because it ran in families. When he saw that thalassemia was much more prevalent where malaria also was present, he came to the hypothesis that the mutations in these families likely persisted because it offered some protection against malaria in these malaria-endemic geographies."
Based on his observations, Haldane theorized that "because the red blood cells were small in those with certain types of anemias, the malaria parasite had a harder time getting into and thriving inside these cells," Dr. Williams explained. "He was ahead of his time in his ability to put these two complicated diseases together."
For this first edition of "Blood Beyond Borders," ASH Clinical News spoke with Dr. Williams and other thalassemia specialists about the history and prevalence of the diseases in the Mediterranean region and the burden to patients and health systems.
Two Seemingly Unrelated Diseases
The term thalassemia derives from the Greek name "Thalassa," which in Greek mythology represented the spirit of the sea. Even though thalassemias are found in people around the world, the name was coined because many of the first cases of thalassemia were observed in the Mediterranean Basin, with families passing the mutations down through generations.
The hereditary hemoglobinopathy involves alterations in the globin chains that make up the hemoglobin molecule. The disease is classified as either alpha or beta thalassemia depending on whether the alpha or beta hemoglobin chain harbors a mutation. Four genes (two from each parent) are needed to make enough alpha or beta globin protein chains; alpha or beta thalassemia trait occurs if one or two of the four genes are missing or altered. The severity of thalassemia depends on how many of these genes are affected – the higher the number, the higher the symptom burden.2
Malaria is an ancient, mosquito-borne disease that, according to a recent DNA analysis of 2,000-year-old remains in Sardinia, has been present in the Mediterranean Basin by the Roman period.3 Several factors contribute to the prevalence of malaria in these areas: Female Anopheles mosquitoes infected with the Plasmodium parasite that causes malaria lay their eggs in shallow, still, fresh water such as puddles and hoof prints – both of which are abundant throughout tropical countries during rainy seasons. Malaria transmission also is more frequent in areas where the warm and wet weather season is longer, resulting in a longer mosquito lifespan.
Despite substantial global progress to curb and eliminate malaria, the disease is still a substantial public health problem around the world. The National Institute of Allergy and Infectious Disease reports that approximately 3.2 billion people worldwide are at risk for the disease. Similarly, the World Health Organization estimates that about half of the world's population is at risk. As of 2017, 90 countries and regions reported cases of malaria transmission.4
Many countries in the Mediterranean, including Greece, had eradicated malaria by the late 1970s but saw an uptick in the number of imported cases as a result of increased international travel, climate changes, and the movement of immigrants from malaria-endemic countries.5
Confirming the Connection
In 1954, the geneticist Anthony C. Allison, PhD, confirmed Haldane's hypothesis while working in Kenya – though for sickle cell anemia. In sickle cell anemia, the HBB gene is mutated, but, unlike in beta thalassemia, the mutation does not affect the abundance of beta hemoglobin. With his research, Dr. Allison found that individuals heterozygous for the mutation in the beta hemoglobin associated with sickle cell anemia have a relative resistance to malaria.6
Then, in the late 1970s, when researchers were able to culture malaria parasites in the laboratory, another group confirmed Dr. Allison's observations: P. falciparum infection of red blood cells with the sickle cell mutation increased cells' rate of forming the sickle shape, and the parasites were killed under these conditions.7
Yet, for thalassemia, establishing exactly how the disease protects against malaria has proven challenging, Dr. Williams said, and efforts are further complicated by the presence of additional genetic polymorphisms that are quite common and can reverse the protection. This occurs despite the presence of a so-called protective hemoglobin mutation. For example, a beta hemoglobin mutation on its own is protective against malaria, but if the individual also has a mutation for sickle cell anemia, the two mutations essentially cancel each other out and the individual is susceptible to malaria infection.8
The proposed mechanisms through which the alpha and beta hemoglobin mutations guard against malaria are categorized as either immune-related or cellular. These include better immune clearance, decreased survival of malaria parasite inside red blood cells, and decreased parasite capacity for invading the red blood cells.
In 2008, a joint team from the New York University School of Medicine and the University of Oxford, working with children in Papua New Guinea who have alpha thalassemia, found that their red blood cells were unusually small and more abundant, resulting in a mild form of anemia, compared with red blood cells of children without the genetic mutation that leads to the thalassemia.9 They went on to show that the alpha thalassemia resulted in an advantage against malaria infection.
Severe malaria resulted in an as high as a 50-percent decrease in red blood cells, but children with mild alpha thalassemia were able to tolerate this loss because they already had up to 20 percent more red blood cells to start with, compared with children without thalassemia.
"There has never been a clinical study that has definitively shown that a beta thalassemia mutation is strongly protective against malaria," Dr. Williams said, but researchers and clinicians have no doubt that these genes are indeed protective against malaria, as RBC characteristics are the only traits that come up as positive in studies of malaria protection.10
Still, there is no clear and irrefutable mechanism about how either alpha or beta thalassemia protects against malaria on which the research community can agree, according to Dr. Williams. "It is difficult to study these conditions in the lab because the red blood cells from patients are inherently prone to oxygen damage and stress," he explained. "When we do experiments with them in the lab, we can find things that look abnormal, but whether those results actually reflect what is going on in vivo is difficult to know because the cells become damaged by the lab manipulations," he explained.
Last but not least, establishing a strong connection between malaria and beta thalassemia mutations is made even more difficult by the fact that many of the places where beta thalassemia has remained are no longer hotspots for malaria.
"In Greece, malaria was still prevalent about 100 years ago because there were many more lakes where malaria-carrying mosquitos could lay eggs," Antonis Kattamis, MD, told ASH Clinical News. Dr. Kattamis is head of the division of pediatric hematology/oncology at the National and Kapodistrian University of Athens and the Aghia Sophia Children’s Hospital in Athens, where he treats patients with thalassemia. "Most of the lakes have dried up in the last century, so we haven't had malaria for many years."
The Burden of Thalassemia in the Mediterranean Basin
Like malaria, thalassemia also was once highly prevalent in these areas: The estimated carrier rate for a thalassemia-related mutation in the Mediterranean region is between 8 and 15 percent.11 Based on this rate, Dr. Kattamis said, clinicians would expect to see about 200 to 250 cases annually. But awareness campaigns in Greece, Italy, and other countries have dramatically decreased thalassemia rates.
In his practice, Dr. Kattamis said he sees about 380 patients with thalassemia on a regular basis, or about 12 percent of the approximately 3,000 patients in Greece who require regular care for their thalassemia. Most of the patients are older, given the decreased rate of new thalassemia cases.
People with severe thalassemia present with symptoms a few months to one year after birth, Dr. Kattamis said. "With severe thalassemia, babies do not grow well and may have jaundice, and patients bring their children in because they are seeing a failure to thrive."
"If a person is homozygous for a beta- or alpha-thalassemia mutation, he or she has no effective hemoglobin protection," Dr. Williams explained, "and after the first few months of life, the individual is chronically anemic and dependent on blood transfusions." Without this therapy, patients otherwise could die from anemia-related complications, including cardiac failure.
However, lifelong transfusions can lead to complications, like iron overload. "The red blood cells that patients receive are rich in iron, and these individuals don't have good ways to excrete the iron, so we then have to treat them with iron-chelating medications," he explained. These medications, called chelators, bind to excess iron, effectively soaking it up. If left untreated, iron overload can lead to chronic iron toxicity, endocrine problems, and cardiac or hepatic failure.
Apart from transfusions, a young patient with a sibling donor also can also undergo a curative bone marrow transplant. According to Dr. Kattamis, approximately one in five or six patients undergoes such a procedure.
New drug therapies are being developed as alternatives to chronic red blood cell transfusions and transplantation. For example, luspatercept, a first-in-class erythroid maturation agent, is designed to enhance late-stage erythropoiesis and reduce the need for transfusions. In the phase III BELIEVE trial, 70 percent of patients with transfusion-dependent beta-thalassemia experienced a greater-than-33-percent reduction in their transfusion burden. At the 2018 American Society of Hematology Annual Meeting, principal investigator Maria Domenica Cappellini, MD, from the University of Milan in Italy, commented that the agent is a potential new therapy for "this very demanding disease. These are young adult patients transfusing three units of blood every three weeks for all their lives, so [the reduction in transfusion burden with luspatercept] has a substantial impact."12
Gene therapies also are on the horizon. Earlier this year in the New England Journal of Medicine, researchers published results from two companion phase I/II trials in showing that treatment with gene therapy reduced or eliminated the need for red blood cell transfusions in patients with severe disease.13 "Gene therapy with the LentiGlobin drug product succeeded in overcoming a principal limitation of [bone marrow transplant], which is a lack of a histocompatible donor," the authors noted.
Together, prevention programs and new therapeutic options have improved the prognosis for thalassemia, to the point that it is now considered a chronic disorder. Dr. Kattamis noted efforts that are under way to identify optimal blood transfusion therapies and management of related complications, noting that, "with treatment, patients have a fairly good life expectation, and about 70 percent will live to age 50." But, as with any other chronic condition in any other geographic area, he said, survival and quality of life depend on the development and adherence to a treatment plan. â€”By Anna Azvolinsky
- Haldane JBS. The rate of mutation of human genes. Hereditas. 1949;35:267-73.
- National Institutes of Health. Genetics Home Reference. "Beta thalassemia." Accessed December 11, 2018.
- ViganÃ³ C, Hass C, RÃ¼hli FJ, Bouwman A. 2,000 year old Î²-thalassemia case in Sardinia suggests malaria was endemic by the Roman period. Am J Phys Anthropol. 2017;164:362-70.
- World Health Organization. "Malaria." Accessed December 11, 2018.
- Opi DH, Ochola LB, Tendwa M, et al. Mechanistic studies of the negative epistatic malaria-protective interaction between sickle cell trait and Î±+thalassemia. EBioMedicine. 2014;1:29-36.
- Allison AC. The distribution of the sickle-cell trait in East Africa and elsewhere, and its apparent relationship to the incidence of subtertian malaria. Trans Royal Soc Trop Med Hyg. 1954;48:312-8.
- Friedman MJ, Roth EF, Nagel RL, Trager W. Plasmodium falciparum: physiological interactions with the human sickle cell. Exp Parasitol. 1979;47:73-80.
- Leffler EM, Band G, Busby GBJ, et al. Resistance to malaria through structural variation of red blood cell invasion receptors. Science. 2017;356:eaam6393.
- Willcox M, BjÃ¶rkman A, Brohult J, et al. A case-control study in northern Liberia of Plasmodium falciparum malaria in haemoglobin S and beta-thalassaemia traits. Ann Trop Med Parasitol. 1983;77:239-46.
- Fowkes FJ, Allen SJ, Allen A, et al. Increased microerythrocyte count in homozygous Î±+-thalassaemia contributes to protection against severe malarial anaemia. PLoS Med. 2008;5:e56.
- De Sanctis V, Kattamis C, Canatan D, et al. Î²-thalassemia distribution in the Old World: an ancient disease seen from a historical standpoint. Mediterr J Hematol Infect Dis. 2017;9:e2017018.
- Cappellini MD, Viprakasit V, Taher A, et al. The Believe trial: results of a phase 3, randomized, double-blind, placebo-controlled study of luspatercept in adult beta-thalassemia patients who require regular red blood cell (RBC) transfusions. Abstract #163. Presented at the 2018 ASH Annual Meeting, December 1, 2018; San Diego, CA.
- Thompson AA, Walters MC, Kwiatkowski J, et al. Gene therapy in patients with transfusion-dependent Î²-thalassemia. N Engl J Med. 2018;378:1479-93.
Highlights of ASH in the Mediterranean
March 15 – 16, 2019
At this new event, co-hosted by the Hellenic Society of Hematology, internationally recognized experts will analyze the latest updates in hematology research from the 2018 American Society of Hematology annual meeting.
Visit hematology.org/Highlights/Mediterranean for more information.