How do a person become back? Or what is the main element disturbed in a person for him/her to be mad? And what causes madness.
Madness/mental distrubance/insanity has multi-factored sources, including genetic, social, hormonal, disease and/or physical injury.
Without knowing details of the specific case, it would be impossible to know the cause(s) or suggest treatment(s).
If you have a specific person in mind, try to get him/her to a physician or psychotherapist for help.