HEMOGLOBIN TUNIS-BIZERTE - A NEW ALPHA(1)-GLOBIN 129-LEU-]PRO UNSTABLE VARIANT WITH THALASSEMIC PHENOTYPE

A Leu-->Pro substitution at position 129 of the alpha(1) globin gene w as detected in three members of a Tunisian family by sequencing the wh ole alpha(2) and alpha(1) DNA. The mutation was verified by dot-blot a llele-specific hybridization as well as by digestion of PCR and RT-PCR products with Nci I, since the alpha(1)(129T-->C) mutation creates an additional recognition site for the above-mentioned enzyme. The alpha (1)(129(H12)Leu-->Pro) substitution disturbs helix H resulting in alph a-thal trait most probably because the unstable alpha-globin chain var iant cannot form alpha beta dimers. A search for the abnormal Hb and f or the abnormal alpha globin chain by isoelectric focusing, carboxymet hyl cellulose chromatography and electrospray ionization mass spectrom etry was negative. In the heterozygous state, the alpha(1)(129(H12)Leu -->Pro) variant is manifested by microcytosis (MCV similar to 73 fl), whereas in the homozygous state there is moderate anaemia with marked microcytosis (Hb 11.6 g/dl, MCV 65 fl).