Intraclonal heterogeneity observed in tumor VH gene sequences at the MGUS stage in case 1 is identified as residual, persisting clones at the myeloma stage of disease.
The mutational frequency of variations in clonal sequences exceededTaq error in sample 1/1 from the MGUS stage, with repeated nucleotide changes seen in 2 clones from separate PCRs (codons 107 and 120) confirming intraclonal heterogeneity. In sample 1/2 from the MM stage, some of these mutations were again identified (codons 68 and 107), clearly excluding Taq error. The mutational frequency of intraclonal variation, however, was comparable with the backgroundTaq misincorporation rate in this sample, suggesting a cessation of somatic mutation at the MM stage. Most likely, variant clones here represent residual MGUS cells, as disease evolution was remarkably rapid. Only informative codon sequences at the nucleotide level are shown, with homology to the donor germ line gene V3-11 depicted as dashes. Mutations repeatedly observed in MGUS and MM samples are marked with an asterisk. Numbers of clones with each sequence varied (n = 1-26). FR3 indicates framework region 3; and JH, joining (H) gene.
