Yes, this is something that the Medical Pro's do not seem to get or understand. A defective gene rarely actually causes someone to develop a problem or illness.It is mostly that the defective gene increases the risk of suffering some form of malnutrition.
In some cases, Iodine deficiency is a major creator of health issues and certain deficient genes aggravate the condition. The same is very true of Vitamin D.
The real problem about this for me is that Jolie has set a very bad example for how to handle the problem. All that I can say is "good thing she was not at risk for brain cancer instead".