Genomic difference analysis by two-dimensional DNA fingerprinting reveals typical changes in human low-grade gliomas

Cytogenetic and molecular analyses such as allelotyping studies have revealed several genetic changes typical for human glial neoplasms. However, most studies to date have involved malignant gliomas and thus are likely to reflect late events of tumor progression. To elucidate the initial events of glial tumor growth, we performed a genome-wide search for genetic alterations in the DNA of 43 low-grade gliomas as compared to the constitutional DNA of the patients' peripheral blood leucocytes using the two-dimensional (2D) DNA fingerprint approach. Reliable results were obtained for 28 blood/tumor sample pairs (13 astrocytomas, 9 pilocytic astrocytomas, 1 oligodendroglioma, 3 oligoastrocytomas, and 2 ependymomas). DNA was digested with the restriction enzyme HaeIII and the resulting fragments were separated on 2D gels according to size and sequence in the first and second dimensions, respectively. Patterns of hundreds of spots were generated by hybridization with four different mini- and microsatellite core probes. A total of 655 to 1,122 spots could be visualized per sample. Comparison of blood and tumor spot patterns revealed two to 11 reproducible changes per patient. Most of the differences were spot losses (77.1%), while the others appeared to be gains or amplifications. Exactly the same changes were found in tumor recurrences which lacked histological signs of progression. When comparing different patients, many of the affected spots tended to cluster in particular areas of the gel as revealed by computer-aided comparison of all spot patterns. Eleven different spot clusters were identified which may correspond to several major deletion targets. This study provides the basis for the future molecular cloning of the candidate tumor suppressor genes affected by the common spot losses and will allow new insights into the genetic mechanisms of glial tumorigenesis.