sickle-cell disease

Hereditary chronic blood disorder common among people of black African descent; also found in the eastern Mediterranean, parts of the Gulf, and in northeastern India. It is characterized by distortion and fragility of the red blood cells, which are lost too rapidly from the circulation. This often results in anaemia.

People with this disease have abnormal red blood cells (sickle cells), containing defective haemoglobin. The presence of sickle cells in the blood is called sicklemia. The disease is caused by a recessive allele. Those with two copies of the allele suffer debilitating anaemia; those with a single copy paired with the normal allele, suffer with only mild anaemia and have a degree of protection against malaria because fewer normal red blood cells are available to the parasites for infection.

In the USA there were approximately 65,000 African-Americans suffering from sickle-cell disease in 1996; there were about 5,500 British sufferers. Worldwide, 100,000 babies are born with the disease annually. Those born in developing countries are unlikely to survive for long.

Bone marrow transplantation can provide a cure, but the risks (a fatality rate of 10% and a complications rate of 20%) are so great that it is only an option for the severely ill. US researchers announced in April 1995 that patients treated with a drug called hydroxyurea showed a reduction in the number of sickle cells. The drug works by reducing the amount of defective haemoglobin produced, and reviving the production of fetal haemoglobin. Fetal haemoglobin is not affected by sickling. Partial (40%) bone marrow transplants used during early 2001 in sickle-cell treatment trials in the USA also proved successful in combating the disease.