This 2015 human summary study was of 44 genetic disorders that disrupt the maintenance of epigenetic modifications:
“..making them likely to have significant downstream epigenetic consequences. Interestingly, these patients often demonstrate neurological dysfunction, suggesting that precise epigenetic regulation may be critical for neuronal homeostasis. However, at the same time, it is important to keep in mind that many of these proteins have additional non-epigenetic roles.
Mutations in many of these components have now been linked to a number of well-known causes of intellectual disability. Intellectual disability is generally defined as deficits of intellectual function and adaptive behavior that occur during the developmental period.
Given the opposing activity of many of the components of the epigenetic machinery, the pathogenic sequence in these disorders involves an imbalance of chromatin states..Keeping a subset of genes under “pressure” from two opposing systems may allow the cellular system to rapidly respond to environmental stimuli.
These disorders, on average, have unusual phenotypic breadth..Similarly, there is a shift in distribution toward a higher number of organ systems affected.
In addition to developmental phenotypes (multiple congenital anomalies), in some cases there appear to be ongoing defects that remain consequential in post-natal life. An example of the latter is the hippocampal memory defects seen in many of the mouse models.
This raises the question whether cells undergoing neurogenesis and synaptogenesis are particularly sensitive to subtle defects of the epigenetic machinery and downstream epigenetic abnormalities..A major remaining question is whether neurogenesis defects and/or abnormalities of synaptic plasticity are a unifying pathophysiological process.”
The researchers also made a good representation of the 44 genetic disorders on a wheel graph. I look forward to further research that includes non-genetic disruptors of epigenetic modifications.
http://genome.cshlp.org/content/25/10/1473.full “The Mendelian disorders of the epigenetic machinery”