We used high-resolution SNP genotyping to identify regions of genomic gain and 
loss in the genomes of 212 medulloblastomas, malignant pediatric brain tumors. 
We found focal amplifications of 15 known oncogenes and focal deletions of 20 
known tumor suppressor genes (TSG), most not previously implicated in 
medulloblastoma. Notably, we identified previously unknown amplifications and 
homozygous deletions, including recurrent, mutually exclusive, highly focal 
genetic events in genes targeting histone lysine methylation, particularly that 
of histone 3, lysine 9 (H3K9). Post-translational modification of histone 
proteins is critical for regulation of gene expression, can participate in 
determination of stem cell fates and has been implicated in carcinogenesis. 
Consistent with our genetic data, restoration of expression of genes controlling 
H3K9 methylation greatly diminishes proliferation of medulloblastoma in vitro. 
Copy number aberrations of genes with critical roles in writing, reading, 
removing and blocking the state of histone lysine methylation, particularly at 
H3K9, suggest that defective control of the histone code contributes to the 
pathogenesis of medulloblastoma.