The Epigenetics of CHARGE Syndrome

In biology, we continue to appreciate the fact that the DNA sequence alone falls short when attempting to explain the intricate inheritance patterns for complex traits. This is particularly true for human disorders that appear to have simple genetic causes. The study of epigenetics, and the increased access to the epigenetic profiles of different tissues has begun to shed light on the genetic complexity of many basic biological processes, both physiological and pathological. Epigenetics refers to heritable changes in gene expression that are not due to alterations in the DNA sequence. Various mechanisms of epigenetic regulation exist, including DNA methylation and histone modification. The identification, and increased understanding of key players and mechanisms of epigenetic regulation have begun to provide significant insight into the underlying origins of various human genetic disorders. One such disorder is CHARGE syndrome (OMIM #214800), which is a leading cause of deaf-blindness worldwide. A majority of CHARGE syndrome cases are caused by haploinsufficiency for the CHD7 gene, which encodes an ATP-dependent chromatin remodeling protein involved in the epigenetic regulation of gene expression. The CHD7 protein has been highly conserved throughout evolution, and research into the function of CHD7 homologs in multiple model systems has increased our understanding of this family of proteins, and epigenetic mechanisms in general. Here we provide a review of CHARGE syndrome, and discuss the epigenetic functions of CHD7 in humans and CHD7 homologs in model organisms.