Progeria
Progeria was a genetic disease which occurred very rarely among Human children until it was eradicated in the 22nd century. Progeria caused children to age much more rapidly than normal, usually leading to an early death.

In 2374, progeria was the only disease The Doctor could think of when Chakotay was suffering from progeria-like symptoms, though it would have been the first case in two centuries and the first ever adult diagnosis.

It was later revealed that Chakotay's condition originated in Srivani medical experiments. ()

External link
 

dE: Progeria
Medical conditions