The most common clinically relevant Hb variants are Hb S (beta codon 6 GAG;Glu ->GTG;Val)., Hb C (beta codon 6 GAG;Glu-> AAG;Lys), Hb D-Punjab (beta 121 GAA;Glu->CAA;Gln), Hb O-Arab (beta 121 GAA;Glu->AAA;Lys), and Hb E (codon 26 (GAG;Glu -> AAG;Lys). These variants can be characterised and presumptively diagnosed using haemoglobin electrophoresis and High Performance Liquid Chromatography (HPLC). For a definitive diagnosis DNA analysis is offered. Sickle cell disease: Seventy per cent of sickle cell disease is caused by homozygosity for the sickle cell mutation located at codon 6 of the beta-globin gene (GAG;Glu ->GTG;Val). This amino acid substitution alters the structure of the globin molecule so that it crystallizes and deforms the red cell into a sickle shape under hypoxic conditions. Twenty-nine per cent of cases are compound heterozygotes for Hb S and Hb C. Less than 1% account for Hb Sβ thalassaemia followed by rarer genotypes of Hb S/D Punjab, Hb S/Lepore and Hb S/O-Arab. Other Hb variants: Most Hb variants are benign affecting both the alpha and beta globin genes. Alteration of the charge of the Hb molecule is detected by haemoglobin electrophoresis, HPLC and Isoelectric Focusing (IEF). Clinical disorders caused by Hb variants include chronic haemolysis, high and low oxygen affinity Hb variants, hypochromic microcytic anaemia e.g. Hb E, Hb Lepore and hyperunstable Hbs. All these variants are identifiable by direct sequence analysis and/or direct mutation analysis.
Factors affecting results or interpretation: Presence of heparin anticoagulant will inhibit PCR applications. Clotted samples are unsuitable for DNA analysis. Samples must be clearly labelled with the patients first name, surname, D.O.B, hospital number and the date the sample was taken. The details on the sample must correspond to the request form. Unlabelled samples will not be accepted.