MODERATE REDUCTION OF BETA-GLOBIN GENE TRANSCRIPT BY A NOVEL MUTATIONIN THE 5'-UNTRANSLATED REGION - A STUDY OF ITS INTERACTION WITH OTHERGENOTYPES IN 2 FAMILIES

We have identified two individuals of Greek Cypriot origin with thalas semia intermedia. Molecular analysis has shown that each individual is a compound heterozygote for a previously described beta degrees thala ssemia allele and a novel mutation, C --> G in position +33, in the 5' untranslated region of the beta globin gene. In both families the bet a +33 allele is associated with the same beta haplotype (-++-+++) sugg esting that it is likely to be of a single origin. beta-cDNAs from nor mal and mutant beta alleles were isolated from peripheral blood reticu locytes using the technique of reverse transcription-polymerase chain reaction. Because the beta +33 (C --> G) mutation creates a cutting si te for the restriction enzyme NlaIV, we could demonstrate by different ial restriction analysis that the beta gene with +33 mutation showed 2 5% to 35% residual activity compared with normal. The additive effect of this moderate deficit in beta globin production with the beta degre es thalassemia mutation would explain the clinical phenotypes observed in the two probands. In contrast, two siblings of one proband who wer e also compound heterozygotes for the same beta thalassemia mutations, as well as heterozygotes for a nondeletional alpha thalassemia varian t, and two other compound heterozygotes for the beta +33 and a beta(+) thalassemia allele were completely asymptomatic. Individuals heterozy gous for the beta +33 C-G mutation alone are clinically and hematologi cally silent, with normal red blood cell indices and normal levels of hemoglobin (Hb) A(2). A direct relationship between genotypic and phen otypic severity is clearly demonstrated in these cases with obvious im plications for prenatal diagnosis. (C) 1996 by The American Society of Hematology.