Molecular screening for haemoglobin constant spring.

Haemoglobin H/Constant Spring is an important cause of severe haemoglobin H disease, but the Constant Spring protein is difficult to detect by electrophoresis. A technique for allele specific polymerase chain amplification of the 3'-end of the alpha 2 globin gene improved detection of the alpha cs alpha haemoglobin variant in DNA samples by slot-blot hybridisation. The alpha cs alpha mutation was confirmed in subjects that had been previously diagnosed by haemoglobin electrophoresis, and it was also detected in patients who were negative by protein electrophoresis. 10 of 103 unrelated Laotians with HbE were alpha cs alpha heterozygotes. Of these, 3 were negative to the normal probe because they had -alpha 3.7/alpha cs alpha with a single alpha globin deletion. 5 samples did not amplify or hybridise to either probe because they had deletions of both alpha 2 globin regions. The gene frequency for alpha cs alpha is about 0.05 for Laotians. This technique, which is highly specific and sensitive for rapid detection of the alpha cs alpha mutation, is suitable for clinical diagnoses and population studies. The true incidence of alpha cs alpha may prove to be greater than previously suspected from protein electrophoresis.