The present application generally to the diagnosis and treatment of diseases resulting from the alteration of chromatin boundaries between topologically-associated domains. In particular, the present application relates to detection of mutations causing DNA hypermethylation phenotypes, CpG methylation within CTCF binding motifs, and aberrant gene expression caused by altered chromatin topology. Applicants show that IDH mutant gliomas exhibit hyper-methylation at CTCF binding sites, compromising binding of this methylation-sensitive insulator protein. Applicants also demonstrate that loss of CTCF at a domain boundary permits a constitutive enhancer to aberrantly interact with the receptor tyrosine kinase gene PDGFRA, a prominent glioma oncogene. Thus, Applicants have uncovered that IDH mutations may promote gliomagenesis by disrupting chromosomal topology and allowing aberrant regulatory interactions that induce oncogene expression.