Molecular characterization of Hb D-Ibadan [beta87(F3)Thr-->Lys] in combination with Hb S [beta6(A3)Glu-->Val] and with beta+-Thalassemia: report of two cases.

Hb D-Ibadan [beta87(F3)Thr-->Lys] is a common variant in the Nigerian population, which has been reported in association with Hb S [beta6(A3)Glu-->Val] and with beta-thalassemia. Unlike the Hb S/Hb D-Los Angeles [beta121(GH4)Glu-->Gln] combination, compound heterozygosity for Hb D-Ibadan and Hb S does not result in a sickling disorder. We report the first case of a combination of Hb D-Ibadan with beta+-thalassemia, and the first observation of Hb S/Hb D-Ibadan in the African-American population. In both cases, the characterization of Hb D-Ibadan was achieved by sequencing of the genomic DNA. Although protein based methods such as isoelec-trofocusing and high performance liquid chromatography may suggest that the "D-like" variant is different from Hb D-Los Angeles, the definitive identification of the variant by structural analysis or molecular genetic methods should be undertaken, particularly in newborn screening programs when the variant is found in combination with Hb S.