Caused by over-gaming. The most common cause is hand-held consoles, the most prominent now being the awkwardly designed Nintendo DS. It causes the the hand to cramp up while attempting to play videogames.
"Now to play some 'Super Mario 64 DS' ...arrgghh... my hand! ..it won't move! AAAH LOOK AT ME! ...don't look at me... Loo~ook at meeee...