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sickle cell anaemia

(Science: haematology) disease common in races of people from areas in which malaria is endemic.

The cause is a point mutation in the allele that codes for the beta chain of haemoglobin with a substitution of (valine for glutamic acid at position 6. The defective haemoglobin (hbS) crystallizes readily at low oxygen tension.

In consequence, erythrocytes from homozygotes change from the normal discoid shape to a sickled shape when the oxygen tension is low and these sickled cells become trapped in capillaries or damaged in transit, leading to severe anaemia.

In heterozygotes, the disadvantages of the abnormal haemoglobin are apparently outweighed by increased resistance to plasmodium falciparum malaria, probably because parasitised cells tend to sickle and are then removed from circulation.

symptoms include joint pain, acute abdominal pain, and ulcerations of the lower extremities.

Origin: Gr. Haima = blood An abnormality in the formation of red blood cells caused by a mutation on chromosome eleven that is responsible for the production of functional haemoglobin. The resultant phenotype of the sufferer is evident in the malformation of red blood cells, where.