Isochromosome 22q- was identified by in situ hybridization of abl gene in a case of CML in blastic crisis. A 19-year-old male had been treated with busulfan for Ph1 positive CML. Two years later, he developed blastic crisis with a type of tumor formation and died in the full developed leukemic conditions. At the stage of blastic crisis, almost all Ph1 chromosomes seemed to be disappeared and many small metacentiric chromosomes were found, instead of Ph1 chromosomes. In situ hybridization of the metaphase chromosomes by 3H-labelled v-abl (2.3 kb) resulted in highly significant labelling on these small metacentric chromosomes and band 9q34. Therefore, the small metacentric chromosomes were identified to be isochromosome of translocated #22 chromosome; i (22q-), originated from Ph1 chromosome.
By in situ hybridization of abl gene, the karyotype in blastic crisis was determined: 52, XY, +X, +Y, -4, +5, -9, +17, -18, -19, -22, +mar1, +mar2, del(7)(p11), +der(9) t(9;22)(q34;q11), +i(22q), +i(22q-), +der(19) t(1;19)(q11;q13), +der(19) t(1;19)(q11;q13). Thus, in situ hybridization of genes, those chromosomal localization have been mapped, seems one of the useful tool for the analysis of complicated chromosome abnormalities.
