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Specific sites on human chromosomes appear to have a tendency to rearrange in so-called "sporadic translocations," which are found in approximately 1 of 1000 metaphases from peripheral blood lymphocyte cultures. We now present data that implicates four sites in the human genome as displaying this distinct type of chromosomal instability (7p13, 7q34, 14q11, and 14q32). Chromosome 14q11 was found to be involved in sporadic translocations most often, followed by 7p13 greater than 7q34 greater than 14q32. The 14q11 locus also shows the highest frequency of spontaneous sister chromatid exchange. It is proposed that these sporadic translocations involving chromosomes #7 and #14 arise following recombinational errors occurring at sites of T- and B-cell genes known to be located at these four sites. Evidence is presented that in some cases "fixation" of a sporadic translocation might be involved in malignancy of lymphoid origin.

We describe herein a translocation, t(1;3)(p36;q21), that was found in the bone marrow of a patient with acute myelomonocytic leukemia preceded by a long lasting myelodysplastic phase. An identical translocation has been reported in three other myelodysplastic patients. one of whom also developed an acute myelomonocytic leukemia. The possible significance of this specific translocation is briefly discussed.

A translocation t(1;7)(p11;p11), previously reported in patients with myelodysplasia or leukemia has been found in seven new cases. The present report briefly reviews the cytogenetic and clinical features of 22 patients with this translocation. The majority of these patients had a history of occupational or therapeutic exposure to toxic substances or radiation. Trisomy 8 or 21 were the most common additional abnormalities, especially in leukemic patients. The t(1;7) should be added to the group of specific cytogenetic abnormalities observed frequently in secondary myelodysplasia and leukemia.

Eight patients with various hematologic disorders had an identical chromosomal aberration in their bone marrow or unstimulated peripheral blood, a translocation t(1;7) interpreted as t(1;7)(p11;p11). The translocation chromosome replaced one normal chromosome #7; therefore, the karyotype of the abnormal cells was trisomic for 1q and monosomic for 7q. Including four cases from the literature, a total of 12 patients (4 women, 8 men) with this translocation are known at the moment. The translocation does not seem to be associated with a specific disorder, but almost all patients had a preleukemic syndrome during some stage of their disease. It is very remarkable that 11 of the 12 patients lived in the Netherlands, and 7 patients had a history of iatrogenic exposure to alkylating agents or irradiation; one patient was a radiation worker and another one had a history of toxic exposure to chloramphenicol. It is suggested, therefore, that the t(1;7) is a possibly induced chromosomal aberration with a clearly nonrandom geographic distribution.