By Joshua Green
A study published, in the November 17th issue of the journal Cell, suggests there are epigenetic modifications that are common between individuals of rare and common forms of autism. The study itself was headed by co-senior study authors Shyam Prabhakar (from the Genome Institute of Singapore) and Daniel Geschwind (from the David Geffen School of Medicine at UCLA). The study also opens up the idea that this common trait, seen in individuals with autism, could be the cause or basis of the diverse manifestations of autism.
What what did they actually spot (with a dumbed down explanation)
The paper talks of a “epigenetic modification”. Something that is epigenetic, in a biological context, is something that ‘arises from non-genetic influences on gene expression’. It is known generally that environmental and genetic factors contribute to autistic spectrum disorders (ASD). Many studies have focused on looking at structural changes to the genome, for example, however there has been a shift in the studies which now focuses on factors that do not affect the DNA sequence of an individual. Epigenetic modifications are changes in genetic activity that does not alter DNA sequences.
Researchers have been previously looking at a chemical modification of DNA known as methylation. Methylation is an epigenetic mechanism that cells use to express genes. It can be used to ‘fix’ non-expressed genes from the “off” position. It is argued that this method ignores the complicated nature of gene expression associated with ASD conditions. In this new study the role of histone acetylation with ASD was explored.
The study reports how the researchers focused on a ‘tag’ which is known as an acetylation mark. This tag, called H3K27ac, was used as a sign of gene activation. The researchers analysed post-mortem brain samples of individuals and found that 68% of the total sample shared a ‘common histone acetylation pattern’ despite the other large amount of environmental factors and genetic factors causing a ASD condition affecting the samples. It was also found that a strong correlation, after 12 months from birth, linked gene activation in the brains to increased acetylation observed. This link that was established lends itself to the conclusion that acetylation has a significant role in the relevant genes, associated with ASD conditions, being expressed. This 12 month after birth analysis is possible due to researchers using ‘BrainSpan’ which is an ‘atlas’ of a developing brain.
The authors are planning to follow up this study with further research questions. This study is seen to be powerful, however, it shows more about shared processes between autistic individuals rather than establishing causal links between the modifications and ASD conditions. There is speculation that, due to how these processes point to specific genes and pathways in ASD-individual’s brains, new targets could be established for novel drug delivery. These drugs could be used to treat ASD conditions in some manner, however, there still needs to be much more extensive research.