This 2018 German review was comprehensive for its subject, epigenetic control of variation and stochasticity in metabolic disease. I’ll focus on one aspect, phenotypic variation:
“Phenotypic [Mendelian] variation can result both from gain- and loss-of-function mutations. Because of the extreme interconnectivity of cell regulatory networks, even at the cellular level, predicting the impact of a sequence variant is difficult as the resultant variation acts:
- In the context of all other variants and
- Their potential additive, synergistic and antagonistic interactions.
This phenomenon is known as epistasis.
∼98.5% of our genome is non-protein-coding: it is pervasively transcribed, and its transcripts can support regulatory function. Among the best functionally characterized non-coding RNAs (ncRNAs) arising from these sequences are microRNAs (miRNAs)
Environmental [non-Mendelian] variation or ‘stimuli’ occurring during critical windows of susceptibility can elicit lifelong alterations in an individual’s phenotype. Intergenerational metabolic reprogramming [in fruit flies] results from global alterations in chromatin state integrity, particularly from reduced H3K27me3 and H3K9me3 [histone] domains.
The broad variation of fingerprints in humans is thought to depend to a large degree on stochastic variation in mechanical forces. These clear examples of inducible multi-stable or stochastic variation highlight how little we know about the landscape of potential phenotypic variation itself.
Consensus estimates of heritability for obesity and T2D are ∼70% and ∼35% respectively. The remaining, unexplained component is known to involve gene–environment interactions as well as non-Mendelian players.”
Although the above graphic displays transgenerational inheritance for humans, the reviewers didn’t cite any human studies that adequately demonstrated causes for and effects of transgenerational epigenetic inheritance.
I’ve read the cited Swedish and Dutch studies. Their designs, methods, and “correlate with” / “was associated with” results didn’t provide incontrovertible evidence from the F0 great-grandparents, F1 grandparents, F2 parents, and F3 children. It’s necessary to thoroughly study each generation to confirm definitive transgenerational epigenetic inheritance causes and effects.
As noted in How to hijack science: Ignore its intent and focus on the 0.0001%, there aren’t any such published studies to cite. Researchers urgently need to do this human research, and stop using these poor substitutes  to pretend there are already adequately evidenced transgenerational epigenetic inheritance human results.
I downgraded the review for treating research of this and other subjects as faits accomplis. It’s opposite ends of the evidential spectrum to state “how little we know about the landscape of potential phenotypic variation,” and in the same review, speciously extrapolate animal experiments into putative human results.
https://www.sciencedirect.com/science/article/pii/S2212877818301984 “Epigenetic control of variation and stochasticity in metabolic disease”
 As an example of the poor substitutes for evidence, a researcher referred me to the 2013 “Transgenerational effects of prenatal exposure to the 1944–45 Dutch famine” which is freely available at https://obgyn.onlinelibrary.wiley.com/doi/full/10.1111/1471-0528.12136 as a study finding human transgenerational epigenetic inheritance.
The methods section showed:
- The study’s non-statistical data was almost all self-reported by a self-selected sample of the F2 grandchildren, average age 37.
- No detailed physical measurements or samples were taken of them, or of their F1 parents, or of their F0 grandparents, all of which are required as baselines for any transgenerational epigenetic inheritance.
- No detailed physical measurements or samples were taken of their F3 children, which is the generation that may provide evidence for transgenerational findings if the previous generations also have detailed physical baselines.
The study’s researchers drew enough participants (360) such that their statistics package allowed them to impute and assume into existence a LOT of data. But the scientific method constrained them to make factual statements of what the evidence actually showed. They admitted:
“In conclusion, we did not find a transgenerational effect of prenatal famine exposure on the health of grandchildren in this study.”
Yet this study is somehow cited for evidence of human transgenerational epigenetically inherited causes and effects.