No evidence of trisomy 12 or t(11;14) by molecular genetic techniques in chronic lymphocytic leukemia cells with a normal karyotype.

Chromosome analysis of B-cell mitogen-activated cells from patients with B-cell chronic lymphocytic leukemia (CLL) show clonal abnormalities in approximately one half of the cases. Among the most frequent aberrations are trisomy 12 and t(11;14). In the other half, no clonal chromosomal abnormalities are found. We wished to determine whether these CLL clones are cytogenetically normal or whether the apparently normal karyotype results from an inability of the malignant cells to enter metaphase in vitro, leaving only the few remaining normal cells to be karyotypically studied. Probes that can detect restriction fragment length polymorphisms (RFLPs) on chromosome 12, which makes it possible to determine the copy number of this chromosome, as well as bcl-1 probes that can detect t(11;14) were used. Of 13 CLL cases with normal karyotypes, none showed evidence for either trisomy 12 or t(11;14). This finding indicates that CLL cases with an apparently normal karyotype do not have two of the most common clonal chromosomal aberrations and may be karyotypically normal. The study also shows that Southern blot analyses, using probes that can detect RFLPs on chromosome 12, can be used for rapid and simple detection of trisomy 12 in CLL patients.