There are two main groups of structurally abnormal haemoglobins in human beings including the thalassaemias. The polymorphic haemoglobins comprise four abnormal haemoglobins (Hb) with high frequencies. The best known is the sickle-cell gene. The sickle-cell gene is found with a frequency of up to 20% in some East African tribes and is common throughout most of central and west Africa. The disease has a wide and irregular distribution and can also be found in the Indian subcontinent, South Arabia, Scicily, Greece and Turkey.
Heterozygotes for thalassaemia show high levels of A2, and the biochemical lesion of retardation of the synthesis of the beta-polypeptide haemoglobin chain. This form is widespread in the Mediterranean region including Greece, France and Turkey. It is also common in the middle east such as Israel, Iran and Iraq). It occurs in India, south east Africa as well as the East Indies. Thalassaemia H2’s occur in up to 20% of the afflicted in Sardinia and other parts of Italy. Typical thalassaemia H2 cases have elevated levels of H2 with up to 11% in southern Liberia.
Haemoglobin C shows H2’s in as many as 30% in some tribes in northern Ghana and the adjacent High Volta. Either side of these regions the incidence decreases and is restricted mainly to west Africa. Haemoglobin E is widespread in south east Asian countries. The frequency of H2′ is up to 35% in Cambodia, but may be an over-estimate. Both haemoglobin E and thalassaemia are common in many south east Asian populations.
Lower frequencies are found with the borderline haemoglobin polymorphisms. Lower frequencies are found in certain populations. In India several populations show only 1 to 2% for HbD, which is also the level for Algeria. Three haemoglobin variants are found in the Punjab, the Gujerat and Cyprus. It is known that, using analysis of the peptides, that these D variants are distinct from one another. It is worth noting that haemoglobin K and N occur with a frequency of 0.5 to 2% in many tribes in west Africa. Among the Berbers of Algeria up to 13.7% of haemoglobin is similar to HbK. Another polymorphism is HbO or Buginese X where 1% of the Buginese tested in positive Sulawesi (formerly Celebes) but absent in others.
Abnormal foetal haemoglobins have been found that include Bart’s or gamma chains. There is the Alexandra type and the Augusta-1 which is entirely composed of beta-polypeptide chains. Abnormal foetal haemoglobins are widely distributed in tropical countries that include Africa, Singapore, and Greece. The Bart’s Hb and adult HbH are thought to be associated with a variant of thalassaemia (which consists entirely of beta-polypeptide chains that affect the alpha-chain. There are numerous Hb’s in still lower frequencies.
Derived from lecture notes at Oxford Polytechnic (1986).