PROLIFERATION ENHANCEMENT BY SPONTANEOUS MULTIPLICATION OF CHROMOSOME-7 IN RHEUMATIC SYNOVIAL-CELLS IN-VITRO

Mosaic trisomy of chromosome 7 is known to occur in a variety of non-n eoplastic hyperproliferative disorders. In long-term cell cultures est ablished from rheumatic synovium with mosaic trisomy 7, we observed a continuous increase in the proportion of cells with trisomy 7 to over 50% by the 10th in vitro passage. Simultaneous in situ hybridization w ith a repetitive chromosome-7-specific DNA probe and fluorescent Ki-67 labelling showed a strong correlation between trisomy 7 and an elevat ed proliferation index in cultured rheumatic synovial cells. Moreover, we observed a fraction of rapidly proliferating cells with up to eigh t copies of chromosome 7 as the sole cytogenetic change. Frequent soma tic pairing of centromeres of two chromosomes 7 in interphase nuclei s uggests either atypical non-disjunction with a persisting centromere o r selective endoreduplication of chromosome 7.