Abnormal HAEMOGLOBIN formation occurs in the haemoglobinopathies, which are hereditary haemolytic anaemias, genetically determined and related to race. The haemoglobin may be abnormal because: (1) there is a defect in the synthesis of normal adult haemoglobin as in THALASSAEMIA, when there may be an absence of one or both of the polypeptide chains characteristic of normal adult haemoglobin; or (2) there is an abnormal form of haemoglobin such as haemoglobin S which results in sickle-cell disease (see ANAEMIA). This abnormality may involve as little as one amino acid of the 300 in the haemoglobin molecule. In sickle-cell haemoglobin, one single amino-acid molecule – that of glutamic acid – is replaced by another – that of valine; this results in such a de?cient end product that the ensuing disease is frequently severe.
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