Exaggerated CpH methylation in the autism-affected brain.
Shannon E Ellis, Simone Gupta, Anna Moes and 2 others
PMID 28316770WHAT IT FOUND
Autistic brain tissue showed no significant differences at specific gene sites compared to controls.
However, it displayed a global increase in methylation at non-CpG sites. This pattern was linked to repetitive genome regions and human-specific regulatory areas, suggesting broad epigenetic changes rather than single-gene defects.
Key findings
01Analysis of post-mortem brain tissue found no individual CpG or CpH sites that were significantly differentially methylated between autism cases and controls.
02There was a significant global increase in methylation at CpH sites in autistic brains, with 65.2% of sites showing hypermethylation.
03Hypermethylated CpH sites were enriched in repetitive genomic regions, human-specific 'beacon' regions, and areas with deactivating histone marks.
STILL TO COME
How it was doneWhat they found
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What it does not show
The study used RRBS, which only sequences CpG-rich regions, so methylation changes in other parts of the genome were not measured. The sample size was small (63 brains total), and the study had 80% power only to detect mean methylation differences of 2.6% or larger. The method cannot distinguish between methylated cytosine (5mC) and hydroxymethylated cytosine (5hmC), so some observed 'methylation' changes might reflect 5hmC levels. The direction of effect for some previously reported regions did not match earlier studies, and the raw data for these overlaps did not account for covariates.
Declared interests
Funded by the Simons Foundation and the National Institute of Mental Health.
The easy way to misread this
Do not interpret the global CpH hypermethylation as a diagnostic marker or a target for treatment. The study found no significant differences at any specific gene site, and it remains unclear whether these broad epigenetic changes cause autism, result from it, or are benign.