I was hoping that the Epigenetics Tsunami would have abated a bit by now, but it’s still washing over the public. And the new video below, produced by TED-Ed, doesn’t help, for it distorts what we know about epigenetics. The organization should be named “TED-anti-ED”:
Just a few of the erroneous claims that you’ll hear in the video:
- All of differential regulation of genes during development (how an original undifferentiated cell turns into an organism having diverse tissues) is caused by epigenetic markers on those genes or on the histone proteins that are the scaffolds for genes. That’s not correct. The differential regulation occurs through the differential expression of transcription factors and small RNA molecules that activate or inactivate genes, with the heritability across mitotic generations caused by positive feedback. Any associations between “epigenetic markers” and gene expression are probably due to the modification of genes after they’re already been expressed or suppressed by transcription factors. Ibn other words, the association is not causal, but a correlation. See here for further explanation.
- The difference between identical twins is due to different epigenetic markers caused by their different life experiences. Again, this is not known; any associations may be correlations rather than the markers causing differential expression of identical genes in identical twins.
- Inherited epigenetic markers (methylated DNA bases in genes) can be passed on to future generations, so that an environmentally-induced change in the genetic material, affecting morphology, physiology, or behavior, could be passed on to future human generations. While this is the case for up to two or three generations in some species, no long-term changes of that type are known (ergo “epigenetic changes” cannot be the basis of a kind of Lamarckian evolution). Further, this is not known to happen in humans, although there is some evidence that parental experiences can affect the offspring’s phenotype or behavior—for only a generation or two. The video contends that “Your mother’s or your father’s experiences as a child, or choices as adults, could actually shape your own epigenome.” There is not a SHRED OF EVIDENCE for that claim. (Note that the video’s title is “How the choices you make can affect your genes.”)
- A healthy diet, exercise, and avoidance of exposure to contaminants can give you a healthy epigenome. Shades of Chopra! Can “epigenetic cleanses” be far behind? That’s just complete hogwash.
- Epigenetics can explain the origin of cancer, heart disease, mental illnesses, and other diseases. In other words, the study of epigenetics can help us cure disease. In fact, there’s no evidence for this contention either. In a piece in the July 1 New York Times, “Growing pains for field of epigenetics as some call for overhaul“, Carl Zimmer highlights a new paper in PLoS Genetics by Ewan Birney, George Davy Smith and John M. Greally (reference and free link below)—a paper that severely criticizes the evidence that diseases can be caused by epigenetic modifications. It entirely possible that such modifications, if they’re real, are likely to be the consequences of disease.
Zimmer’s piece says this:
In May, Duke University researchers claimed that epigenetics could explain why people who grow up poor are at greater risk of depression as adults. Even more provocative studies suggest that when epigenetic marks change, people can pass themto their children, reprogramming their genes.
But criticism of these studies has been growing. Some researchers argue that the experiments have been weakly designed: Very often, they say, it’s impossible for scientists to confirm that epigenetics is responsible for the effects they see.
Three prominent researchers recently outlined their skepticism in detail in the journal PLoS Genetics. The field, they say, needs an overhaul.
“We need to get drunk, go home, have a bit of a cry, and then do something about it tomorrow,” said John M. Greally, one of the authors and an epigenetics expert at the Albert Einstein College of Medicine in New York.
Among other criticisms, he and his co-authors — Ewan Birney of the European Bioinformatics Institute and George Davey Smith of the MRC Integrative Epidemiology Unit at the University of Bristol in England — argue that in some cases, changes to epigenetic marks don’t cause disease, but are merely consequences of disease.
And here’s one way that this claim has been investigated:
Some studies, for example, have found that people with a high body mass index have unusual epigenetic marks on a gene called HIF3A. Some researchers have suggested that those marks change how HIF3A functions, perhaps reprogramming fat cells to store more fat.
If that were true, then drugs that reverse these changes might be able to help obese people lose weight. But Dr. Smith and his colleagues have found that overweight subjects experienced epigenetic changes to HIF3A only after they put on weight.
And one more caveat:
Dr. Greally and his colleagues note another source of confusion: Normal genetic variation leads some people to produce different epigenetic marks than others.
If researchers were to find that alcoholics carry an unusual epigenetic mark, for instance, that wouldn’t necessarily mean that it resulted from heavy drinking. These people may have a genetic variation that puts them at risk of alcoholism and, perhaps coincidentally, creates an unusual epigenetic mark on their DNA.
Dr. Greally said these possibilities have been neglected because scientists have been so captivated by the idea that epigenetic marks can reprogram cells.
“Since you don’t talk about anything else, you interpret the results solely through that little sliver of possibility,” he said.
He and his colleagues go so far as to claim that no published results on the links between epigenetic marks and disease “can be said to be fully interpretable.”
From what I know (and I’ll admit this isn’t my field), these criticisms are on the mark. But read the PLoS Genetics article below if you want to go deeper into this field. In the meantime, it’s just irresponsible for TED to promulgate the video below, which makes about as many mistakes as can be made in a five-minute presentation. I’d suggest that TED consider removing this misleading presentation. In the meantime, my advice to the layperson reading popular articles about epigenetics is this: unless the article is by Carl Zimmer, take everything it says with a grain of salt.
The misguided TED video: