Thalassemias also called in their major form anemia or Cooley’s disease (Thomas Benton Cooley), are forms of hereditary anemia, part of hemoglobinopathies (qualitative or quantitative abnormalities in the hemoglobin of red blood cells). This results in reasonably significant anemia. There is also an enlargement of the spleen and deformities of the skull and long bones. The popular name also knows the disease of “Mediterranean disease.”

Even if there are two kinds of thalassemia (alpha and beta), due to the rarity of the first, the thalassemias “without precision” correspond, in fact, to beta thalassemias.

Caused

These are genetic diseases that affect the production of hemoglobin. The latter is formed by four subunits, two alpha and two beta, in the case of adult hemoglobin (HbA). We speak of alpha thalassemias or beta thalassemias, depending on the type of subunits reached.

Alpha Thalassemia

Alpha-thalassemias are characterized by a deficiency of the globin-alpha chain in hemoglobin. They affect the synthesis of the three types of hemoglobin: HbA, HbA2, and HbF, because all contain the alpha chain; in these cases, life is only possible thanks to the formation of significant amounts of abnormal hemoglobin consisting only of chains whose synthesis is not hindered: HbH and Barts Hemoglobin.

These rare diseases have a localized ethnic distribution (some regions of Africa, Saudi Arabia, India, or Thaïland).

Beta thalassemia
Beta-thalassemias, also called “red blood cell diseases,” are characterized by the absence of the β chain of hemoglobin. Only the synthesis of HbA is hindered. Nearly 200 alleles have been described, concerning either the β-chain gene or, much more rarely, regulatory genes. They affect 60,000 children at birth worldwide every year.

In the world
The thalassemic gene is widely distributed among the populations occupying the shores of the Mediterranean (Thalassa = the sea in ancient Greek), in Corsica, in Italy, and in particular in the Po delta, in Sardinia, in Sicily; in Greece, Crete, Cyprus, Lebanon, Syria, and Turkey. Other outbreaks (perhaps due to a different allele) exist in Thailand, Laos, India, China, the Philippines, and some regions of Africa.

The highest frequencies (carriers of the gene) are found in Cyprus (14% of the population), Sardinia (10%), and Southeast Asia6. Due to migrations and interbreeding, the gene is found in all parts of the world, in 1.5% of the world’s population (80 to 90 million people).

The overall prevalence of β-thalassemia is estimated at 288,000 cases, of which 60 to 80% require treatment. The annual incidence of symptomatic cases would be of the order of 1 per hundred thousand inhabitants in the world and 1 in ten thousand in Europe.

In the United States and the European Union, the prevalence is estimated at 15,000 cases, with 1,500 children being born each year with the disease. In most other regions (North Africa, the Middle East, and Asia), access to treatment is limited and patients are exposed to an increased risk from an early age.

Diagnosis of beta thalassemia

Thalassemia is clinically presented in three degrees of severity: major, intermediate, and minor.

Major form
Thalassemia major is secondary to a homozygous form (two alleles affected in the same way, on both chromosomes) or to a compound heterozygous form (a deficient allele but in a different way on each chromosome).

The diagnosis is most often made at 6 months to 2 years old. Anemia is typically microcytic and hypochromic. The hemoglobin level may be less than seven g/100 mL.

Hemoglobin electrophoresis makes the diagnosis show a constantly increased percentage of HbF while the percentage of HbA2 is normal or elevated.

Free hyper bilirubin ism is the witness of hemolysis.

Minor and intermediate form
These forms include moderate anemia that does not require repeated transfusions.

For beta-thalassemia minor: there is no clinical symptomatology. However, there may be slight splenomegaly. Biology shows a microcytosis without anemia or only moderate, a pseudo-polycythemia with red blood cells in a number greater than 5 to 7 million/mm, a hypochromic, and an HbA2 level greater than 3.5%.

In the case of frank anemia, it is necessary to look for an aggravating cause and determine the martial status to make the differential diagnosis with iron deficiency anemia (no iron deficiency in thalassemia).

Treatments

Thalassaemia minor is most often asymptomatic and does not require specific treatment. The aim of screening for heterozygotes is to identify couples at risk to inform and manage them (genetic counselling)

Definitives

Marrow transplantation is only proposed in severe forms.
It can be done by allogeneic bone marrow transplant, with a marrow donor: used in many blood diseases, notably leukaemia.