The Relative Levels of Different Types of β-mRNA and β-Globin in BFU-E Derived Colonies from Patients with β Chain Variants; Further Evidence for Somatic Mosaicism in the Hb Costa Rica Carrier [β77(EF1)HISÅG]

Abstract

We have identified and quantitated the different types of mRNA in single BFU-E derived colonies from Hb S and Hb Atlanta [β75(E19)Leu→Pro] heterozygotes and observed that the normal and mutated mRNAs were present in equal quantities. Similar studies for the different protein products gave less accurate data because high performance liquid chromatography methods were not sensitive enough for the analysis of a single colony, and as many as five colonies needed to be combined. The level of Hb S (∼40%) was the same as in red cell lysates of the Hb S heterozygote, while that of the unstable β-Atlanta chain was lower than expected from the values observed in red cells. Similar studies for a carrier of the stable Hb Costa Rica [β77(EF1) His→Arg] which was reported to be the result of a somatic cell mutation (1) gave quite different data. Dot-blot analysis with ³²P-labeled probes and allele specific amplification methodology identified numerous colonies with β^A-mRNA only, while 12-15% of the colonies contained both β^A -and β-Costa Rica-mRNA. This limited distribution of the β-Costa Rica-mRNA was confirmed by hemoglobin analysis with anion exchange high performance liquid chromatography. These results are considered to provide additional and convincing evidence for a somatic mosaicism for the CACc`C mutation at codon 77 of the β gene which occurred during the development of the embryo and results in the presence of only some 6-8% of the abnormal Hb Costa Rica in the circulating red cells.