Alzheimer's disease

Alzheimer's disease was a disease that would make people senile, and thus affected memory. It was quite common for victims to remember snippets from their childhoods or lives. (TV: Out of Time)

Ace asked the Seventh Doctor if Time Lords could suffer from Alzheimers. He told her they got much worse diseases. (PROSE: Relative Dementias)

Cases

 * Bea Nelson-Stanley was an Alzheimer's sufferer. (TV: Eye of the Gorgon)
 * Alan Ellis began to suffer from the disease. (TV: Out of Time)
 * Doctors believed that Katie Russell had Alzheimer's. She in fact had a parasitic tumour. (TV: Fragments)
 * Henrietta Goodheart suffered from Alzheimer's but still remained lively. (PROSE: Beautiful Chaos)