Phobias may be passed down through generations

Do you suffer from a phobia that can't be easily explained by some traumatic event in your life? Have you always been terrified of going out on the ocean, but you've only ever seen it in pictures, or been afraid of spiders without ever having a bad experience with one? Well, according to some new research, it's possible you might have your father or grandfather to blame, then.

Researchers Brian Dias and Kerry Ressler — at Emory University School of Medicine — have published a new study in Nature Neuroscience that shows fear memories can apparently be passed down from generation to generation. They exposed mice to a particular odour (the same one used to simulate smells like almonds, cherries and strawberries) and conditioned them to fear that odour. This, in turn, actually changed the expression for the specific gene that responds to the odour, making the mice physically more sensitive to it. When these mice then went on to conceive offspring, the offspring also showed the same increased sensitivity, and this carried on to affect the 'grandchildren' of the fear-conditioned mice as well.

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The idea behind how this fear response is being passed on to subsequent generations is through what's called epigenetics. This is still a fairly new branch of research, which deals with how the sequence of a person's DNA can remain unchanged, but the expression of genes in the sequence can change over time, due to environmental factors. Although not exactly embraced by all, there's some thought that these epigenetic changes may be passed on to subsequent generations, just like genetic information is passed down.

There's been some skepticism about the study, of course. One of the issues is that the 'signal' for the heightened sensitivity to this odour would have to make it to the testes, through either the nervous system or the blood stream, to affect the sperm. However, whereas the nervous system and the blood stream certainly have access to the testes, on the whole, they apparently do not have direct contact with the tubes where the sperm are formed. So, the mechanism for how the information is transmitted is still unknown.

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Still, given how specific the evidence is, the study is compelling, and other researchers are interested in what kind of implications this may hold for human phobias, anxiety and even post-traumatic stress disorder (PTSD).

As of yet, there's nothing that says it's definitely epigenetics that's passing on these environmentally-induced traits, and there's also nothing yet that says this can be applied to human genetics and behaviour. However, according to what University of Cambridge geneticist Anne Ferguson-Smith told Virginia Hughes, over at National Geographic, there's a "growing list of compelling models telling us that something is going on that facilitates transmission of environmentally induced traits."

For now, Dias and Ressler are moving on to the next stage of the study, which is to see what happens when the original mice have offspring after they're conditioned to lose their fear of the odour. These new offspring might show the same sensitivity as their earlier siblings, or they may not show any sensitivity at all. It'll be interesting to see which it is, and what direction the research will go in from there.

(Photo courtesy Getty Images)

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