Joker's Disease

 I've seen a lot of forums and blogs complaining about Joker's Vrolik's Syndrome and his movements, ship crashes and relationship with EDI, but in my mind, there is only one burning question, Why did the ME writers decide to give him this problem in the first place? It's so unusual to see anyone in a video game who suffers from any diseases or syndromes, let alone one that would so severally impact the character's life. I want to know what the original thought was behind creating the character of Jeff "Joker" Moreau, but I've been unable to find anything. Does anyone have any information from the game developers as to why Joker is the way he it?