This 2017 review provided evidence for epigenetic effects on a disease widely considered to be of genetic origins:
“..for a T1D [type 1 diabetes] identical twin the concordance rate (both twins affected)..is consistently less than 100%, which implies a non-genetically determined effect. However, the concordance rate declines with age at diagnosis of the index twin, indicating that in adult-onset T1D the genetic impact is limited, and certainly lower than that in childhood-onset disease.
Genes associated with T1D are well-established and have four broad functions..However, T1D is unlikely to be a single disease since there is disease heterogeneity..the incidence of T1D has even increased several-fold in the last 30 years-a timeframe which rules out genetic evolution. In addition, studies of the incidence of T1D in migrant populations have shown a convergence towards the risk of the host population.
Alongside histone modifications and transcription factors, several cis-regulatory elements, including enhancers, promoters, silencers and insulators, are crucial to the function of the genome..There are more than a million enhancers; therefore, many more than there are genes, so that a number of genes are regulated by the same enhancer, which may co-localise with CpGs. Gene enhancers can be found upstream or downstream of genes and do not necessarily act on the closest promoter..Enhancers may be accompanied by insulators, which are located between the enhancers and promoters of adjacent genes and can limit phenotypic gene expression despite genetic activation.”
The review was weak in a few areas. The authors repeated a laughable claim for gross national product as a non-genetic effect for Type 1 diabetes. They also made other hyperbolic statements such as “..this observation illustrates the power of epigenetic analysis to identify those cells which are actively using the genes associated with a given tissue, given that all cells contain every gene..” that were out of place with the review’s evidential bases.
https://link.springer.com/article/10.1007/s11892-017-0916-x “The Role of Epigenetics in Type 1 Diabetes”