MENTALLY CHALLENGED, otherwise known as Mentally retarded, mental retardism, PWN and other such titles, occurred when idiotic dudes couldn't decide what part of the Universe they wanted to be in, or their affiliations within the Clone Wars. So therefore many people who met them were like "Dude, you're mentally retarded." Even God was challenged in this insulting manner, but then He reflected by dropping a bombshell on Mount Sorrow, therefore proving his dick was actually a rock.
Palpatine had it. Yep, he was the one who commenced it. Palpy and all the geeks out there became obsessed with immortality, and therefore they became so obsessed with this idea that it was like they decided to wipe out all the Younglings in the Jedi Temple just to gain the idea. Palpatine indeed had the sad consciousness that he was really retarded, so therefore he approached God with the question "Am I mentally retarded?" Kyle therefore slept with his wife and pushed Palpy into the elevator shaft.
There is no cure. Sad but true.
...Well, technically, there is is cure, but revealing this secret would be much more insane than briefly revealing who cut the sock. I mean, come on, look at it. It's practically as bad as this.
Palpatine was rumored to have discovered the Cure, but then he realized how awesome that dude was and snuffed it.
Some people had to live with it. Sad, but true. Yoda was so mentally challenged that he couldn't even string a decent sentence together, but of course many Wookies were prone to the same affliction. Even Luke didn't lack this terrible bug which spread around the Universe like a poisonous gaslamp, killing everything it touched. And touched is the real word. Because if Anakin hadn't become afflicted with this illness, than many people wouldn't have snuffed it, and nothing exciting would've occurred in the Galaxy. Wowee!