Sara Jane Mckenzie

Molecular diagnosis of the Philadelphia chromosome translocation. A comparison of isotopic and chemiluminescent Southern blotting.

Southern blotting using radiolabeled probes is a well established technique for the detection of the Philadelphia translocation in the diagnosis of chronic myelogenous leukemia (CML). However, the use of radioisotopes in the clinical setting is often problematic. Because of this we investigated the use of a digoxigenin-labeled probe and chemiluminography in the detection of the Philadelphia translocation. In this study DNA was extracted from 19 bone marrow or blood samples from patients with CML or other malignancies and subjected to Southern blotting with a probe specific for the Philadelphia translocation, Phl/bcr3. The probe was labeled with either, 32P or digoxigenin to determine the relative sensitivity and specificity of autoradiography and chemiluminography in the molecular diagnosis of the BCR/abl fusion gene. All 19 samples were tested by both methods. All blots were performed and interpreted by individuals blind to the initial patient diagnosis. In addition, 12 samples (6 positive for CML, 6 negative for CML as determined by Southern blotting with 32P-labeled probe) were subjected to triplicate Southern-blot analyses, with three separate lots of digoxigenin-labeled probe to assay batch to batch variability in the efficacy of the probe. Radiolabeled and digoxigenin-labeled probes resulted in identical diagnoses in all cases. All results obtained by molecular analysis correlated perfectly with the clinical diagnoses of the patients from whom the samples had been obtained. Preanalysis of patient samples with different batches of digoxigenin-labeled probe gave highly reproducible results. With digoxigenin-labeled probe, diagnostic results were obtained after exposure times of less than 1 h at room temperature. Comparable results with radiolabeled probe required the use of enhancing screens and a 3–4-day exposure at −70°C. Overall, we have found the use of the digoxigenin-labeled probe Phl/bcr3 and chemilumines-cence using the substrate CSPD to be at least as good and in some respects superior to the use of radiolabeled probe and autoradiography in the molecular diagnosis of CML.