Autism

Sarah Jane Smith's niece Lily is autistic. This manifests in many ways, including her tendency to scream whenever prevented from doing something she loves, such as playing in the snow, or her habit of attacking other children (simply hitting them. )(PROSE: Lily)

Ryan Scott, who was also autistic, would sing to isolate himself from the world. (PROSE: Into the Silence)

Olivia Jennings thought that the Sixth Doctor might be autistic. (AUDIO: The Curious Incident of the Doctor in the Night-Time)