Is the chromosomal region 9q34 always involved in variants of the Ph1 translocation?

Six variants of the Ph1 translocation are described. The clinical diagnoses were chronic myeloid leukemia (CML) in 5 cases (patients 1-5) and acute lymphocytic leukemia (ALL) in patient 6. Three Ph1 variants were clear complex translocations, involving chromosomes #9, #22, and a third chromosome, i.e., #16, #11, or #14. The other three Ph1 variants appeared as "simple" translocations between chromosome #22 and chromosome #19, #4, or #12 when G- or Q-banding were used. When studied with high resolution R-banding, a small deletion of the terminal part of one chromosome #9 was visible, strongly suggesting that these variants were also complex translocations, i.e., t(9;19;22)(q34;p13;q11),t(4;9;22) (p16;q34;q11), and t(9;12;22)(q34;p13;q11). In the latter two cases, using in situ hybridization techniques, we demonstrated the presence of c-abl sequences on the Ph1 chromosome. This proved the involvement of 9q34 in these two variants. Our proposal is that most, and probably all, variants of Ph1 are complex translocations involving part of 9q34 and that the conjunction of a specific region of 22q11 with a specific segment of 9q34 (carrying the c-abl protooncogene) is essential for the development of Ph1 + CML.