Medulloblastoma arises in the cerebellum and is the most common malignant brain 
tumour of childhood, however its molecular basis is not well understood. To 
assess the role of aberrant epigenetic events in medulloblastoma and identify 
critical genes in its development, we profiled the promoter methylation status 
of 11 candidate tumour-suppressor genes (TSGs; p14(ARF), p15(INK4b), p16(INK4a), 
CASP8, HIC1, EDNRB, TIMP3, TP73, TSLC1, RIZ1 and RASSF1A) in medulloblastoma 
cell lines, primary tumours and the normal cerebellum. Gene-specific TSG 
methylation was a significant feature of both medulloblastomas and the 
cerebellum. Extensive hypermethylation of RASSF1A was detected frequently in 
medulloblastomas but not in the normal cerebellum (41/44 primary tumours versus 
0/5 normal cerebella). In contrast, complete methylation of HIC1 and CASP8 in a 
subset of primary tumours (17/44 and 14/39) occurred against a consistent 
background of partial methylation in the normal cerebellum. These data therefore 
indicate that extensive methylation of RASSF1A, HIC1 and CASP8 are 
tumour-specific events in medulloblastoma. Moreover, methylation of these genes 
in medulloblastoma cell lines was associated with their epigenetic 
transcriptional silencing and methylation-dependent re-expression following 
treatment with the DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine. The 
remaining genes studied showed either low frequency methylation (p14(ARF), 
p16(INK4a), RIZ1; <7% of cases), no evidence of methylation (p15(INK4b), TIMP3, 
TP73, TSLC1), or comparable patterns of methylation in the normal cerebellum 
(EDNRB), suggesting that their hypermethylation does not play a major role in 
medulloblastoma. Our data demonstrate that tumour-specific hypermethylation 
affects only a subset of genes, and does not support the existence of a 
concordant methylation phenotype in this disease. We conclude that epigenetic 
TSG inactivation is a significant feature of medulloblastoma, and identify 
RASSF1A, HIC1 and CASP8 as potentially critical genes in its pathogenesis. 
Furthermore, methylation observed in the normal cerebellum emphasises the 
requirement for appropriate control tissues when assessing the 
tumour-specificity of TSG hypermethylation.