Analysis of the TSC2 gene in human medulloblastoma

Medulloblastoma (MB) represents the most frequent malignant brain tumor of childhood. Recent studies have shown that deregulation of developmental control genes may play an important role in its pathogenesis. Tuberous sclerosis is associated with hamartomas and cortical tubers, consisting of both glial and neuronal cellular components. MBs can also show markers of these lineages, raising the question of the potential involvement of TSC genes in these malignant tumors. Here we investigated tuberous sclerosis 2 (TSC2), one of the two genes responsible for tuberous sclerosis, in sporadic MBs. We analyzed MBs for allelic losses at the TSC2 locus and for the frequency of a polymorphism first described in gangliogliomas. Sixty-eight MBs were examined for this polymorphism located in intron 4, 3 base pairs 5' to the first coding nucleotide of exon 5. The distribution of the alleles was significantly different in MBs as compared to 208 control samples, (P=0.0017, Chi-square test). In MBs the frequency of the rare allele (A2) was 0.184 (18.4%), whereas in the control group it occurred in a frequency of 8.7%. Microsatellite analysis of the TSC2 region in 50 tumors did not identify allelic losses. TSC2 mRNA transcript was detectable via reverse transcription-PCR in all tumors as well as in normal cerebellum. Northern blot analysis of an MB cell line homozygous for the rare allele of the polymorphism and two other cell lines homozygous for the frequent allele revealed normal splicing patterns and normal expression levels of the TSC2 transcript. These findings may indicate that the presence of the rare TSC2 allele is associated with a predisposition for the development of MBs.