Chronic lymphocytic leukemia (CLL) presents a varying incidence of karyotypic abnormalities whose detection is complicated by difficulties in obtaining mitosis for analysis in this type of mature lymphocyte disorder. Since the introduction of molecular cytogenetics (FISH = fluorescent in situ hybridization), applying centromeric probes for chromosome 12 has made it possible to detect a higher percentage of trisomy 12 cases. The objective of the present study was to detect trisomy 12 by FISH (alpha satellite probe) in 13 patients with CLL whose karyotypes by G-banding were either normal or inadequate. Using this method trisomy 12 was detected in three patients in a percentage of positive cells varying from 55.5% to 79%, showing that FISH is a sensitive and highly specific method for trisomy detection and should be routinely performed when the karyotype is normal.
