p53 allelic imbalance in astrocytoma detected using fluorescent PCR of microsatellite repeat polymorphisms.

Previous reports have shown that p53 gene alteration plays an important role in tumourigenesis. Allelic loss of 17p in astrocytomas was detected in previous studies by restriction fragment length polymorphisms (RFLP). In this study we have analysed 47 cases of astrocytic tumours (26 glioblastomas [grade IV], 11 anaplastic astrocytomas [grade III], seven fibrillary astrocytomas [grade II] and three pilocytic astrocytomas [grade I]) for the presence of allelic imbalance at the p53 gene locus using intragenic markers. We used an informative method based on microsatellite polymorphisms at the p53 gene locus and fluorescent PCR. The fluorescently-labelled PCR products were then detected and analysed using an automated DNA sequencer with appropriate software. Seven of 47 (14.9%) cases were homozygous (uninformative). Five of the remaining 40 cases (12.5%) showed allelic imbalance at the p53 locus (three anaplastic astrocytomas [grade III] and two glioblastomas [grade IV]). None of the fibrillary astrocytomas (grade II) or pilocytic astrocytomas (grade I) showed allelic imbalance at the p53 locus. These results suggest that allelic imbalance at the p53 locus is not frequent and when it does occur is in high grade tumours.