Autism

Autistic Spectrum Disorder was a mental condition.

Sarah Jane Smith's granddaughter Lily was autistic. This manifested in her in many ways, such as her tendency to attack other children, and the fact that she would scream if prevented from doing something she loved, such as playing in the snow. (PROSE: Lily)

Ryan Scott's autism made it so that he 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)