Thalassemia

Overview

Thalassemia variant alleles are common in patients from Africa, Mediterranean countries and parts of the Asian continent. Sickle cell trait is distributed throughout the world with high prevalence in sub-Saharan Africa, some Mediterranean countries and the Middle East.

Alpha-thalassemia

Alpha-thalassemias are caused by gene deletions (sometimes mutations) on one of the 4 alpha globin genes:

• Silent carrier status (1 missing gene) - Asymptomatic with normal red blood cells
• Alpha-thalassemia trait (2 missing genes) - Mild anemia with hypochromia and microcytosis
• Hemoglobin H disease (3 missing genes) - These patients should be referred to a Hematologist

If a patient has any of the alpha-thalassemia alleles and is planning a pregnancy, their partner should also be tested. If there is any risk of hemoglobin H disease or hydrops fetalis (4 missing genes), they should be referred to Medical Genetics for pre-conception counselling.

Beta-thalassemia

Beta-thalassemias are caused by mutations on one of the 2 beta globin genes. The mutations can cause either reduced expression (β+) or absence of expression (β0).

• Beta-thalassemia major (β0/β0 or β0/β+) - Severe life-long transfusion-dependent anemia
• Beta-thalassemia intermedia - Variable severity
• Beta-thalassemia trait (β/β0 or β/β+) - Usually asymptomatic with mild anemia and marked microcytosis

Both major and intermedia patients should be referred to a Hematologist.