The breakpoint of the Philadelphia chromosome 22 in chronic myeloid leukaemia is distal to the immunoglobulin lambda light chain constant region genes.

Somatic cell hybrids containing chromosomes from a patient with chronic myeloid leukaemia were used as a source of DNA for filter hybridizations with immunoglobulin lambda light chain constant region and c-onc probes. The results show that at least part of the human lambda constant region locus remains on the abnormal chromosome 22 (the Philadelphia chromosome) and therefore that this translocation occurs distal to these genes. Further, in the patient studied the c-abl gene has been translocated to the abnormal chromosome 22, thus creating a new genetic linkage between C lambda and c-abl genes.