Sickle cell disease

Sickle cell disease is a genetic and inherited blood disorder that affects hemoglobin morphology and caused red blood cells with a sickle or crescent shape.

Hemoglobin is an essential molecule of the red blood cells (or erythrocytes). The main purpose of hemoglobin is to transport oxygen through the bloodstream.

Normal red blood cells (RBCs) have a biconcave disc shape. The abnormal hemoglobin produced in this disorder, called hemoglobin S, causes the presence of red blood cells more fragile and shaped like sickles or crescents.

Sickle cell disease is a hereditary genetic disorder caused by the mutation of the HBB gene (11p15.4) located on chromosome 11.

It is an autosomal recessive disorder. It means that it requires both altered copies of the gene, one from each parent, to develop the disease.

People who only have mutated gene will carry the disease with no symptoms. Carriers may pass on the condition to his or her own children.

The mutation causes an abnormally develop of the red blood cells. The red blood cells are stiff and sticky and they may lead to anemia and obstruction of blood vessels that may result in clinical manifestations such as pain crisis, necrosis, bacterial infections, etc.

Sickle cell disease is one of the most common genetic disorders worldwide, which affects approximately 50 million people.

It is more common in equatorial Africa, Mediterranean, India, and the Middle East. It is most frequently seen in black people.

Carriers of the sickle cell trait have some resistance against malaria. They have a better survival rate against this infectious disease.

The symptoms are very diverse. There may be people asymptomatic for life, while others have repeated episodes of severe pain (crises) since childhood that require frequent hospitalization.

The symptoms are a consequence of the obstruction of blood vessels and may affect any part of the body. The obstruction may produce ischemia (lack of oxygen) of the affected area, with very intense pain.

The most common complications are:

• Chronic anemia
• Severe pain crises
• Necrosis
• Bacterial infections (pneumonia, meningitis, osteomyelitis, bacteremia)
• Enlarged spleen (sometimes requires spleen removal)
• Stroke (rare)
• Heart attack (rare complication)
• Visual impairment (in case of retinal artery occlusion)
• Priapism (prolonged and painful erection, it is a medical emergency)
• Pregnancy complications

It can also lead to long-term complications, such as:

• Chronic pain
• Heart and lung problems
• Neurological disorders
• High blood pressure and kidney failure
• Chronic ulcers
• Visual impairments

Molecular genetic testing can be performed to detect the presence of the mutated HBB gene.

It is important to study the rest of the family to avoid further transmission to the offspring.

A newborn screening for sickle cell disease is recommended to detect the disorder as soon as possible.

Generally, patients tend to be asymptomatic. Those who suffer pain crises and associated complications require hospitalization.

When symptoms are present, the course of treatment is:

• Intravenous hydration
• Analgesics and narcotics (morphine) to relieve the pain
• Antibiotics (if there are bacterial infections)
• Blood transfusions (in case of severe anemia)

Sickle cell anemia can be prevented through molecular genetic testing of the family and parents to avoid passing the mutation to the offspring.

Other recommendations include:

• Healthy balanced diet and proper hydration.
• Preventive treatment with hydroxyurea (for those who suffer frequent crises).
• Pneumococcal and Haemophilus Influenzae vaccines (for those who have had their spleen removed).