Thalassaemia Classifications
1. Alpha thalassaemia
is due to a deletion or mutation in one or more of the 4 alpha globin gene copies. The more genes affected, the less alpha globin produced. The four different types of alpha thalassaemia include:
Silent Carrier State (1 affected gene). The silent carrier will have normal haemoglobin levels red cell indices which are normal or show a slightly decreased MCH (hypochromia). Carriers can pass on the affected gene to their offspring. Often these individuals are identified only after having a child with HbH disease or alpha thalassaemia trait.
Alpha Thalassaemia Trait (2 affected genes). Patients who have alpha thalassaemia trait have smaller (microcytic), paler (hypochromic) red blood cells and a mild chronic Anaemia but do not generally experience any symptoms. This is an Anaemia that does not respond to iron supplements. Diagnosis of alpha thalassaemia trait is usually by exclusion of other causes of microcytic Anaemia. Confirmatory testing by DNA analysis is available but is not routinely done.
Haemoglobin H Disease (3 affected genes). With this condition, the large decrease in the amount of alpha globin chains produced causes an excess of beta chains which then aggregate into beta4 tetramers (groups of 4 beta chains), known as Haemoglobin H. HbH disease can cause moderate to severe Anaemia and splenomegaly (enlarged spleen). The clinical picture associated with HbH disease is extremely variable, however. Some individuals are asymptomatic while others have severe Anaemia. Haemoglobin H disease is found most often in individuals of Southeast Asian or Eastern Mediterranean descent.
Alpha Thalassaemia Major (also called hydrops fetalis, 4 affected genes). This is the most severe form of alpha thalassaemia. In this condition, no alpha globin is produced, therefore, no HbA or HbF are produced. Fetuses affected by alpha thalassaemia major become anemic early in pregnancy. They become hydropic (retain fluids), and frequently have enlarged hearts and livers. This diagnosis is frequently made in the last months of pregnancy when a fetal ultrasound indicates a hydropic fetus. About 80% of the time the mother will have toxaemia and can develop severe postpartum hemorrhage. Fetuses with alpha thalassaemia major are usually miscarried, stillborn, or die shortly after birth.
Individuals with alpha thalassaemia may be misdiagnosed as iron deficient by unwary doctors, as iron deficiency also leads to small pale (microcytic hypochromic) red cells. It is important that iron therapy in thalassaemic patients is only given when specific iron tests (LINK TO FERRITIN, SERUM IRON, TIBC&TRANSFERRIN) have confirmed iron deficiency. This is especially important in alpha thalassaemia, where there is a small potential for dangerous iron overload to develop.
Alpha thalassaemia is found most commonly in individuals with an ethnic background of Southeast Asia, Southern China, the Middle East, India, Africa and the Mediterranean.