Histone H3 lysine 9 (H3K9) and lysine 27 (H3K27) trimethylation are properties of stably silenced heterochromatin whereas H3K9 dimethylation (H3K9me2) is important for euchromatic gene repression. In colorectal cancer cells, all of these marks, as well as the key enzymes which establish them, surround the hMLH1 promoter when it is DNA hypermethylated and aberrantly silenced, but are absent when the gene is unmethylated and fully expressed in a euchromatic state. When the aberrantly silenced gene is DNA demethylated and reexpressed following 5-aza-2V -deoxycytidine treatment, H3K9me1 and H3K9me2 are the only silencing marks that are lost. A series of other silenced and DNA hypermethylated gene promoters behave identically even when the genes are chronically DNA demethylated and reexpressed after genetic knockout of DNA methyltransferases. Our data indicate that when transcription of DNA hypermethylated genes is activated in cancer cells, their promoters remain in an environment with certain heterochromatic characteristics. This finding has important implications for the translational goal of reactivating aberrantly silenced cancer genes as a therapeutic maneuver. (Cancer Res 2006; 66(7): 3541-9)

Malan syndrome is an overgrowth disorder described in a limited number of individuals. We aim to delineate the entity by studying a large group of affected individuals. We gathered data on 45 affected individuals with a molecularly confirmed diagnosis through an international collaboration and compared data to the 35 previously reported individuals. Results indicate that height is > 2 SDS in infancy and childhood but in only half of affected adults. Cardinal facial characteristics include long, triangular face, macrocephaly, prominent forehead, everted lower lip, and prominent chin. Intellectual disability is universally present, behaviorally anxiety is characteristic. Malan syndrome is caused by deletions or point mutations of NFIX clustered mostly in exon 2. There is no genotype‐phenotype correlation except for an increased risk for epilepsy with 19p13.2 microdeletions. Variants arose de novo, except in one family in which mother was mosaic. Variants causing Malan and Marshall‐Smith syndrome can be discerned by differences in the site of stop codon formation. We conclude that Malan syndrome has a well recognizable phenotype that usually can be discerned easily from Marshall–Smith syndrome but rarely there is some overlap. Differentiation from Sotos and Weaver syndrome can be made by clinical evaluation only.

Mendelian disorders of the epigenetic machinery are a newly delineated group of multiple congenital anomaly and intellectual disability syndromes resulting from mutations in genes encoding components of the epigenetic machinery. The gene products affected in these inherited conditions act in trans and are expected to have widespread epigenetic consequences. Many of these syndromes demonstrate phenotypic overlap with classical imprinting disorders and with one another. The various writer and eraser systems involve opposing players, which we propose must maintain a balance between open and closed chromatin states in any given cell. An imbalance might lead to disrupted expression of disease-relevant target genes. We suggest that classifying disorders based on predicted effects on this balance would be informative regarding pathogenesis. Furthermore, strategies targeted at restoring this balance might offer novel therapeutic avenues, taking advantage of available agents such as histone deacetylase inhibitors and histone acetylation antagonists.