Autism
From Tardis Wiki, the free Doctor Who reference
Sarah Jane Smith's niece Lily was autistic. This manifested 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 or 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)
