Corpus Callosum blogs about the study, "Transgenerational Transmission of Cortisol and PTSD Risk" by Rachel Yehuda and Linda M. Bierer, which discovered that lower cortisol levels were observed in the offspring of Holocaust survivors, suggesting a link between parental experiences of PTSD and an increased risk of their children experiencing PTSD.
Epigenetics is still a new field, but there appears to be great potential for epigenetic models to explain intergenerational changes in genetic expression, an idea that challenges the traditional rejection of acquired traits being transmissible to later offspring. It is possible that the paradigmatic shifts inspired by epigenetics could be to genetics what Einsteinan physics was to Newtonian physics.
In light of this, it is reasonable to predict that in the next twenty years, we will see a wave of new medical and psychological conditions as the children of Iraq War veterans are born and grow up. Perhaps by then we will not only understand why they are affected as they are, but we will be developing treatments and cures to mitigate these impacts.
For a quick introduction to epigenetics, I strongly recommmend Survival of the Sickest, by Sharon Moalem. I am currently reading Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life, by Eva Jablonka and Marion J. Lamb, and while I have not yet gotten to the part on epigenetics, it is a good book for discussing the paradigms and ideas behind the theories of genetics that were developed.