Translocations as a mechanism for homozygous deletion of 13q14 and loss of the ATM gene in a patient with B-cell chronic lymphocytic leukemia.

Chromosomal aberrations detected by fluorescence in situ hybridization (FISH) on interphase nuclei are important prognostic markers in chronic lymphocytic leukemia (CLL). Deletions in 13q14 and in 11q22.3 are two of the most frequent aberrations in this disease entity (55 and 18%, respectively) and are usually effected by interstitial deletions. Here, we report on the case of a 66-year-old woman with CLL who was analyzed by conventional metaphase cytogenetics as well as fluorescence in situ hybridization. Deletion-specific probes detected a homozygous loss of two anonymous loci in chromosomal band 13q14 in parallel with a heterozygous loss of the ATM gene located in chromosomal band 11q22.3. Karyotype analysis indicated reciprocal but unbalanced translocations involving chromosomes 3, 11, and 13. Deleted sites on 13q14 appeared to be located within the breakpoint regions of the translocations. We show that mechanisms other than interstitial deletions may lead to loss of critical chromosomal regions in CLL.