Haemoglobinopathy

Sickle-cell anaemia is hereditary disease found widely in tropical Africa and also in American blacks whose ancestors came from that part of Africa. It is characterize by sickle-shaped (crescentic) red blood cells formed under low oxygen conditions.

Change in the shape of red blood is due to the presence in hem of a defective type of haemoglobin called sickle-cell haemoglobin, or haemoglobin S. The molecule of haemoglobin S has a different shape from that of the normal haemoglobin A molecule.

Because of their inflexibility, the sickle-shaped cell, cannot easily squeeze through narrow capillaries. The sickled cells get stuck in the small capillaries and reduce circulation the regions supplied by these vessels. The sickled cells also break down easily, decreasing the number of RBC leading to anaemia.

Poor circulation and anaemia are other secondary effects of the pleiotropic genes. These effects deprive the tissues of oxygen. This also produces a variety of other symptoms such as tiredness, headache, fever, muscle cramps, poor growth, jaundice, low resistance to infection, and possibly failure of heart and kidney.

Alteration one nucleotide pair in DNA results in the substitution of one amino acid - valine for glutamic acid - which is the sixth amino acid in the beta polypeptide chain of haemoglobin.