THE RELATIVE LEVELS OF DIFFERENT TYPES OF BETA-MESSENGER-RNA AND BETA-GLOBIN IN BFU-E DERIVED COLONIES FROM PATIENTS WITH BETA-CHAIN VARIANTS - FURTHER EVIDENCE FOR SOMATIC MOSAICISM IN THE HB-COSTA-RICA CARRIER [BETA-77(EF1)HIS-]ARG]

We have identified and quantitated the different types of mRNA in sing le BFU-E derived colonies from Hb S and Hb Atlanta [beta 75(E19)Leu--> Pro] heterozygotes and observed that the normal and mutated mRNAs were present in equal quantities. Similar studies for the different protei n products gave less accurate data because high performance liquid chr omatography methods were not sensitive enough for the analysis of a si ngle colony, and as many as five colonies needed to be combined. The l evel of Hb S (similar to 40%) was the same as in red cell lysates of t he Hb S heterozygote, while that of the unstable beta-Atlanta chain wa s lower than expected from the values observed in red cells. Similar s tudies for a carrier of the stable Hb Costa Rica [beta 77(EF1) His-->A rg] which was reported to be the result of a somatic cell mutation (1) gave quite different data. Dot-blot analysis with P-32-labeled probes and allele specific amplification methodology identified numerous col onies with beta(A)-mRNA only, while 12-15% of the colonies contained b oth beta(A)- and beta-Costa Rica-mRNA. This limited distribution of th e beta-Costa Rica-mRNA was confirmed by hemoglobin analysis with anion exchange high performance liquid chromatography. These results are co nsidered to provide additional and convincing evidence for a somatic m osaicism for the CAC-->CGC mutation at codon 77 of the beta gene which occurred during the development of the embryo and results in the pres ence of only some 6-8% of the abnormal Hb Costa Rica in the circulatin g red cells.