Autism

Sarah Jane Smith's granddaughter Lily was autistic. This manifested in many ways, including her tendency to scream if prevented from doing something she loved, like playing in the snow, or her habit of attacking other children. (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)