alpha-thalassaemia masked by beta gene defects and a new polyadenylation site mutation on the alpha2-globin gene.

We report three examples of chronic anaemia involving complex combinations of alpha- and beta-globin gene defects. The first case had a potential Hb H disease caused by the classic SEA/RW deletions masked by Hb E [beta26(B8)Glu-->Lys] in the homozygous state. The second had an unusual Hb H disease caused by compound heterozygosity for two different alpha2 polyadenylation site mutations masked by a beta-thalassaemia heterozygosity. The third had an intermediate alpha-thalassaemia with considerable anaemia caused by an as yet unknown polyadenylation site (AATAAA>AATAAC) mutation in combination with a common RW deletion masked by a common Hb C [beta6(A3)Glu-->Lys] heterozygosity. Diagnostic methods, genotype/phenotype correlations and the chance of overlooking these combinations during risk assessment in a multiethnic society are discussed.