Usually manifests itself in eight-year-old boys who, upon infection, will dress in black, sellotaping strips of paper to their arms and legs, cutting out cardboard discs (the same size as we used to use to make large pom poms in the olden days) and marching round the house with serious aspect at all times.
Early signs of contagion include discovering all your YouTube recommendations (based on previous searches) being related to Tron, younger siblings insisting without prompting that they are in fact not Mabel, as you previously thought (having named them that) but in fact QUORRA, and snippings of cardboard (offcuts from home-made identity discs) strewn about the floor.
You are in the full grip of the disease when your offstpring shrieks "I AM NOT CLU! I AM KEVIN!" at you when you try to enter into the spirit of things by entering the youngster's imagination games - always a mistake, as older parents will unstintingly tell you.