This would be so cool! In the beginning, when creating your sim, you could give them a disease or defect at birth or somewhere is the settings be able to turn it off. You could make them have cancer, ...
Obviously there would be a way to turn it off in the settings, like aging, and knowing the Sims, theyw ould definately have a cure in a special store of some sort. This would just be interesting for people who think the sims is too easy, and it would also be hard having enough money to pay for the cure, (Like real life) It's just an idea.