If a translocation is followed by loss of one of the two derivative chromosomes, the result is an unbalanced translocation, showing monosomy for the segments making up the lost derivative. We have found that in most unbalanced translocations, a third event takes place: a morphologically normal copy of one of the two translocation participants is added to the karyotype. This creates a complex abnormal karyotype with monosomy, disomy, and trisomy for different segments of the translocation participants. We have examined 82 unbalanced translocations from 77 patients, 73 of whom had a myeloid hemopoietic malignancy. Acquisition of a normal copy of a translocation participant was found in 49 translocations. Twenty-five of these showed trisomy for 1q. In 16 of the 25 1q-trisomic cases the translocation was t(1;7)(q10;p10) (trisomy for 1q and monosomy for 7q). Patients with trisomy for 1q were younger than the remaining patients. Whereas those with t(1;7))(q10;p10) showed brief survivals, those with trisomy 1q but monosomy for regions other than 7q survived longer than the remaining patients. We conclude that most unbalanced translocations involve a partial trisomy, that 1q is trisomic far more frequently than any other segment, and that partial trisomy is associated with patient age and survival.
Copyright 2000 Wiley-Liss, Inc.