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 con trol genes may play an important role in its pathogenesis. Tuberous scleros is is associated with hamartomas and cortical tubers, consisting of both gl ial and neuronal cellular components. MBs can also show markers of these li neages, raising the question of the potential involvement of TSC genes in t hese malignant tumors. Here we investigated tuberous sclerosis 2 (TSC2), on e 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 exam ined for this polymorphism located in intron 4, 3 base pairs 5' to the firs t coding nucleotide of exon 5. The distribution of the alleles was signific antly different in MBs as compared to 208 control samples, (P=0.0017, Chi-s quare 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%. Microsat ellite analysis of the TSC2 region in 50 tumors did not identify allelic lo sses. 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 pat terns and normal expression levels or the TSC2 transcript. These findings m ay indicate that the presence of the rare TSC2 allele is associated with a predisposition for the development of MBs.