Tough to say.
From what we understand so far, people may be prone to it at varying levels. Genes, and the ability to create neural links though external resources seem to be the driving factor of keeping a healthy brain, healthy.
There may be a smoker who runs through an entire pack on a daily basis and has been doing so for the past 20 years, yet shows no signs of lung cancer. On the other hand, you may pick up a cigarette tomorrow and smoke casually for the next 5 years and develop symptomatic signs of lung disease, as your genetic makeover was simply more prone to the illness.
The same analogy can apply to MMA.