Sickle-Cell Disease Classification

Sickle cell disease is a health condition that has the potential to lead to a number of complications, due to the altered shape of haemoglobin in the blood.

There are various different types of sickle cell disease, which are classified according to the haemoglobin abnormality. These types include:

• Hemoglobin SS
• Hemoglobin SC
• Hemoglobin Sβ0 thalassemia
• Hemoglobin Sβ+ thalassemia
• Hemoglobin SD
• Hemoglobin SE

Whilst some types are more severe with the potential to be fatal, patients with other types may not experience any symptoms at all. The most common types of sickle cell disease are discussed in more detail below.

Sickle Cell Anaemia (HbSS)

Sickle cell anemia refers to the form of the disease when there is homozygosity for the gene mutation that is responsible for causing the production of sickle haemoglobin. This occurs when a child inherits the sickle gene from both parents and is the most serious form of the disease with the potential for serious complications.

There are various names that can be used to indicate sickle cell anaemia. These may include HBSS, SS disease, sickle cell disease-SS or haemoglobin S. In the United States, sickle cell anemia is the most common form of sickle cell disease and affects 65% of US patients with the disease.

Sickle Cell Disease-SC (HbSC)

Sickle cell disease-SC affects patients with the S/C genotype and involves the inheritance of one sickle gene mutation and one HbC gene mutation. As a result of the two similar gene defects, it is associated with similar symptoms and effects.

It can also be referred to as haemoglobin C with sickling disease or HbSC and is the second most common form of the disease in the United States, accounting for 25% of patients with the disease.

Sickle Beta Thalassaemia

Thalassaemia is another inherited health condition that affects the haemoglobin in the red blood cells. If a child inherits a sickle gene mutation from one parent and a thalassemia gene mutation from the other parent, sickle beta thalassemia can present with characteristics of both blood diseases.

There are two kinds of sickle beta thalassaemia: sickle beta plus thalassaemia (HbS/β+) and sickle beta zero thalassaemia (HbS/β0). These are less common that the previous two types, accounting for 8% and 2% of patients with the disease in the United States respectively.

Sickle Cell Trait (HbAS)

Sickle cell trait refers to individuals that have inherited only one abnormal sickle gene and also possess one normal adult haemoglobin gene. This is known and heterozygous, as there are different genes present, and can people with this type can sometimes be referred to as sickle cell disease carriers.

It is unusual for people with the trait to experience symptoms. However, they have the potential to pass the gene on to any children, who may suffer from sickle cell anemia if the other parent is also a carrier of the gene mutation.

Other Types

There are also some rare types of sickle cell disease, which include:

• Haemoglobin-SD disease (HbSD)
• Haemoglobin-SE disease (HbSE)
• Haemoglobin-SO Arab disease (HbSO)

References

• http://www.ihtc.org/medical-professionals/blood-disorders/sickle-cell-disease/
• http://bestpractice.bmj.com/best-practice/monograph/100/basics/classification.html
• http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2561539/