CHROMOSOME FRAGILITY AND PREDISPOSITION TO CHILDHOOD MALIGNANCIES

In order to clarify the possible connection between autosomal folate s ensitive Fragile Sites (FS) and genetic susceptibility to haemopoetic disease in children we investigated the frequency and distribution of FS in the Peripheral Blood Lymphocytes (PBL) of 56 children with newly diagnosed and untreated haematologic malignancies and their parents. The incidence was compared with that of 146 normal controls (children and adults). In all patients the Bone Marrow (BM) karyotype was also d etermined. Heritable FS were detected in 49 patients (87.5%). 20 child ren had more than one FS and in all cases it was inherited from one of their parents, although there was a significant excess of transmittin g mothers. 19 different FS were identified: 14 common, 4 rare and one, 22q11, which has not been previously reported, but it is considered a s important as it coincides with the cancer breakpoint resulting in th e formation of the Philadelphia (Ph) chromosome. The frequency of FS i n the PBL of the patients was significantly higher than in the control s and this increase was independent of any abnormality detected in the malignant cells of the BM. However, patients with an abnormal BM kary otype displayed increased frequency of FS induction as compared to pat ients with a normal karyotype. In three cases the heritable FS was fou nd to be at or near the breakpoints of the chromosomal rearrangments d etected in the malignant cells. The findings are discussed with regard to cancer specific breakpoints, oncogene loci and sites where viral D NA can be inserted to the genome. The results of this study suggest th at autosomal folate sensitive FS may increase the risk for haematologi c malignancies through a complex mechanism which remains to be clarifi ed.