Types of thalassaemia

What are the different types of thalassaemia?

The main types of thalassaemia are called alpha thalassaemia and beta thalassaemia. (The alpha and beta refer to which haemoglobin gene is affected, and which of the haemoglobin chains is faulty.) There are some rarer types too.

Each type of thalassaemia (alpha and beta) is then classified into more types, according to how severe the condition is. This mainly depends on how many thalassaemia genes are involved. The mildest types are called thalassaemia trait (or thalassaemia minor). The more severe beta types are beta thalassaemia major and beta thalassaemia intermedia. The more severe alpha forms are Hb Barts (very severe) and Hb H disease (moderate). These are explained below. There are also some rarer types of thalassaemia such as delta beta thalassaemia, or combinations of a beta thalassaemia gene with another abnormal haemoglobin gene such as HbE.

Thalassaemia trait (thalassaemia minor)

This means that you carry a thalassaemia gene, but can still make enough normal haemoglobin. So, you will not have any symptoms or problems from the thalassaemia. You will not know you have it unless you have a special blood test. However, it can be useful to know your diagnosis because:

• Some types of thalassaemia trait give you a very mild type of anaemia, where your red blood cells are smaller and paler than usual (described in lab reports as 'microcytic and hypochromic'). This can be mistaken for iron deficiency.
• Your children can inherit the gene. By itself this is not a problem. However, if your partner also has a similar gene, your children might get a double dose of the abnormal haemoglobin gene and could inherit a severe form of thalassaemia. It is possible to arrange tests for parents or for an unborn baby, to see whether the baby could be affected.

There are three types of thalassaemia trait:

• Alpha plus thalassaemia trait. This means that you have one missing alpha haemoglobin gene. (Normally there are four of these genes.) This trait can ONLY cause a problem if your partner has alpha zero thalassaemia trait - in which case your children might inherit Hb H disease (explained below). Apart from that situation, it will not affect you or your children.
• Alpha zero thalassaemia trait. This means you have two missing alpha haemoglobin genes (out of the normal four alpha genes). It will not make you ill, but if your partner also has alpha zero thalassaemia trait, your children might inherit a severe condition called Hb Barts (explained below). Or, if your partner has alpha plus thalassaemia trait, then your children might inherit Hb H disease (see below).
• Beta thalassaemia trait. This means you have one abnormal beta haemoglobin gene (out of the normal two beta genes). It will not make you ill. But, if your partner also has beta thalassaemia trait, then your children could inherit beta thalassaemia major or beta thalassaemia intermedia (see below). Beta thalassaemia trait can also interact with other abnormal haemoglobin genes which are not thalassaemias. For example, if your partner has a gene for sickle cell anaemia, then your children might inherit a serious condition called sickle cell/beta thalassaemia (see below).

Beta thalassaemia major

A person with beta thalassaemia major has two beta thalassaemia genes. Most of their haemoglobin is abnormal and does not work. This causes severe anaemia starting around the age of 4-6 months. Before that, the baby is not affected. This is because until age 3-6 months the baby makes a different type of haemoglobin called fetal haemoglobin which is not affected by the thalassaemia gene. With beta thalassaemia major, you need regular blood transfusions, plus other treatment to prevent complications.

Beta thalassaemia intermedia

As the name suggests, this type is less severe than beta thalassaemia major. You have two beta thalassaemia genes but can make some haemoglobin which works reasonably well. This may be because your particular combination of thalassaemia genes is (in effect) less severe, or because of some other protective factor. Although less severe than thalassaemia major, thalassaemia intermedia does need regular monitoring for life and often needs some treatment to prevent complications.

Sickle cell/beta thalassaemia

This can occur if one parent has a beta thalassaemia gene, and the other parent carries a gene for a different haemoglobin disorder called sickle cell anaemia. If their child inherits one of each gene, the combination is called sickle cell/beta thalassaemia - also called 'sickle cell disease'. This condition behaves like sickle cell anaemia (not like thalassaemia) and is treated in the same way as sickle cell anaemia. See separate leaflet called 'Sickle Cell Disease and Sickle Cell Anaemia' for more detail.

Hb H disease

This is a type of alpha thalassaemia. It is due to having three missing alpha haemoglobin genes (normally each person has 4 of these genes). This can happen if one parent has alpha plus thalassaemia and the other has alpha zero thalassaemia. It usually causes a mild but persistent anaemia. Sometimes Hb H causes more symptoms and is similar to beta thalassaemia intermedia (explained below). Some people with Hb H disease need blood transfusions.

Hb Barts

This is the most severe form of thalassaemia, where all the alpha haemoglobin genes are abnormal or missing. It occurs if a baby inherits two alpha zero thalassaemia genes. In this condition, no normal haemoglobin can be made, even before birth. It is the most serious form of thalassaemia - so serious that the baby will usually die in the womb from severe anaemia. There have been rare cases where the baby was saved by giving blood transfusions in the womb, and then continuing the transfusions after birth.

Link : http://www.patient.co.uk/showdoc/23068993/