ABSTRACT
Each molecule of haemoglobin normally contains four globin chains. At birth, 50-80% of haemoglobin is fetal haemoglobin (HbF=α2γ2) and 15-40% is adult haemoglobin (HbA=α2ß2). A small proportion is HbA2=α2δ2. By 6 months of age HbF represents less than 5% of the total. By 3 years HbA represents 98-99% with one α-chain and one ß-chain inherited from each parent. Sickle cell anaemia (HbSS) is a disorder of haemoglobin synthesis due to a single amino acid substitution (valine for glutamine) in the ß-globin chain. Other ß-chain variants include haemoglobin C (HbC). The thalassaemia syndromes result from impaired globin chain synthesis which may affect either the α-or ß-chains. Each haemoglobinopathy can exist in the heterozygous or homozygous state. Mixed haemoglobinopathies, e.g. HbS/HbC or HbS/ß-thalassaemia, occur and tend to be milder than HbSS.
