Autism

Sarah Jane Smith's granddaughter Lily was autistic. This manifested in many ways, including her tendency to scream when prevented from doing something she loved, 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) Indeed, the Eighth Doctor spoke positively on many autistic children's "phenomenal" abilities to recall shapes and numbers, (PROSE: Fear Itself) a skill the Doctor would often employ to their advantage. (TV: Logopolis, Wild Blue Yonder, et al.)

Behind the scenes

Bethany Black, who appeared in Sleep No More, confirmed that she was autistic. (REF: THWR 250, THWR 251)