Wirth: All efforts to identify a gene responsible for predisposing people to manic-depression have failed. In fact, nearly all researchers now agree that there is no manic-depression gene.  Ttherefore, if these researchers are right, any claim that some people are genetically predisposed to manic-depression is simply false. Chang: I do not dispute your evidence, but I take issue with your conclusion. Many of the researchers you refer to have found evidence that a set of several genes is involved and that complex interactions among these genes produce a predisposition to manic-depression.
The point at issue between Wirth and Chang is whether current research supports the claim that no one is genetically predisposed to manic-depression.