Globin mRNA in beta-thalassemia heterozygotes with different beta-thalassemia alleles and in heterozygotes for hereditary persistence of fetal hemoglobin.

Abstract

Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to determine the alpha 2/alpha 1-, alpha/beta-, and gamma/beta-mRNA ratios in subjects with beta-thalassemia (beta-thal), hereditary persistence of fetal hemoglobin (HPFH), and normal adults. The alpha- and beta-globin gene mutations were characterized with gene mapping, PCR, and DNA sequencing. The average alpha 2/alpha 1-mRNA ratio was the same in normal adults and beta-thal heterozygotes with four alpha-globin genes (2.61-2.63) or with an alpha-thal-2 trait (1.48-1.55). The average alpha/beta-mRNA ratios were 4.47 and 3.84 in normal adults with four alpha-globin genes and with alpha-thal-2 trait (-alpha/alpha alpha), respectively. There was an increase of approximately 50% in beta-thal heterozygotes with transcriptional mutants [-88 (C-->T) and -29 (A-->G)] with lower values (approximately 25%) in those with alpha-thal-2 trait (-alpha/alpha alpha). High alpha/beta ratios were also observed for heterozygotes for nonsense or frameshift mutants located in exon 1 or exon 2. Increases of approximately 150-165% were seen in subjects with RNA processing defects; an exception was the IVS-1-110 (G-->A) mutation with a normal value in the heterozygote. The increases were also less pronounced in heterozygotes for the codon (CD) 121 (G-->T) mutation and the CDs 134-137 insertion/deletion. Normal alpha/(gamma + beta) values were seen in 3 heterozygotes each with a different deletion involving part of the beta-globin gene. The presence of the silent beta-thal allele, -101 (C-->T), in trans to a CD 8 (-AA) allele has a minor effect on the alpha/beta-mRNA ratio. The alpha/beta-mRNA ratio in HPFH heterozygotes was approximately 145% of normal, but with a gamma-mRNA level of 35.4-44.7% the calculated alpha/(gamma + beta) ratio became as in normal adults. The RT-PCR methodology appears useful in expression studies in beta-thal (and HPFH) and values of mRNA appear to correspond to the type of prevailing mutation(s) and concomitant alpha-thal.