To date, there are several disadvantages that have been well documented. First, there's the potential effects of aging, somatic mutation, and improper imprinting. Additionally, there are currently few laws governing ethical control and implementation of genetic manipulation. There is also the problem with the genetically manipulated interbreeding with the natural organisms present in the environment and thus mutating entire generations in ways that we are not able to predict with current technology. When it gest to this point we would be unable to control the effects (good or bad). Many give this idea the term 'genetic pollution'.
