6 Types of Sickle Cell Disorder

Sickle Cell Disorder is an inherited blood disorder which used to be attributed to mainly people of African origin. However over the years especially due to cross culturalization it has been discovered that various form of sickle cell disorder exist. These various types of sickle cell  disorder (disease) occur as a result of mutations in different genes. Bear in mind that over 400 types of abnormal hemoglobin have been found to be associated with sickle cell disease.

HbSS or the genotype SS – this is the most common kind and it is inherited from parents with the ‘S’ gene trait, that is, Mother-HbS(AS) and Father-HbS(AS). Most SS sufferers tend to experience severe symptoms including frequent pain crises, chronic anemia (Low blood count), and multiple organ dysfunction.

HbSC or the genotype SC – this is the second most common kind and it is inherited when one parent has the HbC gene and the other parent has the HbS gene. SC sufferers however experience more significant bone degeneration (deterioration and loss of function), retinopathy (eye damage), acute splenic sequestration (trapping of sickled cells in the spleen), and increased risk of experiencing priapism (a painful erection that occurs without sexual stimulation or arousal, which may result in impotence if not treated. Priapism occurs when blood vessels in the penis are obstructed by sickled cells). In Nigeria, the HbC gene is largely confined to the Yoruba people of the South West for example as found in AC genotype. It is very rare among the Igbos of Eastern Nigeria.

Sickle Beta Thalassemia (Sβ) – this occurs when a person inherits one HbS gene from one parent and one beta thalassemia gene from the other parent. This gene is more common among those of Mediterranean ancestry (particularly Turkey, Cyprus, Greece and Italy).

There are two types of sickle beta thalassemia:

  • Sickle beta plus thalassemia (Sβ+): this is a “mild” form of sickle cell disorder. The red blood cells contain an abnormal hemoglobin called hemoglobin S or sickle hemoglobin in addition to a small amount of the normal hemoglobin called hemoglobin A. The red blood cells have a defect called beta plus thalassemia, which results in cells which are small in size and more pale than usual. Instead of appearing round or doughnut shaped, the red blood cells are somewhat small, pale, and misshapen. Some may appear sickled or banana shaped.
  • Sickle beta zero thalassemia (Sβ0): these sufferers often experience symptoms that are more severe than that of the SS sufferer. This is because the beta thalassemia gene produces no normal hemoglobin.

Sickle Cell SE (HbSE) – this occurs when a person inherits one HbS gene from one parent and one HbE gene from the other parent. Most SE sufferers have mild to moderate anemia (low blood count). There may be no serious symptoms or problems as SE tends to be milder than SS or SC  is most common in Southeast Asian populations. However, under certain conditions such as exhaustion, oxygen deprivation (hypoxia), severe infection, and/or iron deficiency; some mild to moderate anemia, pain crises, gallstones and pulmonary hypertension (high blood pressure in the lungs) may occur. The spleen in younger children with HbSE may be somewhat less effective in removing bacteria from the blood, thereby leading to a higher risk of serious blood infections. Over time, SE sufferers risk damage to the retina.They should be seen regularly by an ophthalmologist (an eye doctor).

Sickle cell SD (HbSD) –  this occurs when a person inherits one HbS gene from one parent and one HbD gene from the other parent and is relatively rare. SD sufferers may experience any and all sickle cell symptoms ranging from mild to severe.

Sickle Cell SO (HbSO) – this occurs when a person inherits one HbS gene from one parent and one HbO gene from the other parent and is rare as well and sufferers may experience any and all sickle cell symptoms ranging from mild to severe.

The types of sickle cell disorder discussed above are the most common variants.

Written by

Maureen Nwachi

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