Posted by Larry Hoover on January 17, 2009, at 20:19:46
There's a new way of looking at genetic influences upon illnesses. How is it that two people with the same genes, such as identical twins, often have one member ill while the other is healthy, even though the disorder is considered to be genetically linked? The answer is non-genetic changes to DNA, modifications superimposed on the genes, called epigenetics. Epi- means "in addition to".
I remember when I was 11, and we were being taught about the development of a human being from one fertilized ovum. One cell was the source of all the different tissues in the body. But we were also taught that nerve cells reproduced to form other nerve cells. Muscle cells begat muscle, and so on. There was an inherent paradox in that. How did cell types differentiate, if they could only reproduce copies of themselves? It turns out that the differentiation is mediated by epigenetic factors, i.e. genes are switched on or off.
Flying in the face of standard genetic theory, epigenetic changes leading to adaptation of a parent to his or her environment can be passed along in germ cells to their progeny. So, it is possible that not only genes, but gene regulation is heritable.
http://biology.mcgill.ca/undergrad/c524a/articles2007/Chandler_Cell128.pdf
A recent paper out of North America's only lab studying epigenetic influences on mental illness offers some insight into epigenetic changes and psychosis in bipolar disorder and schizophrenia.
I wouldn't be surprised to discover that kindling, the idea that recurrence of mental illness becomes more likely the more times it occurs, is actually an epigenetic phenomenon. Or that PTSD is an epigenetic phenomenon.
We're only just scratching the surface on the subject so far, but seeking purely genetic factors for disease may have to take a back seat to epigenetics.
Lar
poster:Larry Hoover
thread:874594
URL: http://www.dr-bob.org/babble/20090104/msgs/874594.html