"Both of them are very childlike now”

Matthew Clark, 39, of Lincoln, England and his brother Michael Clark, 42, last year were diagnosed with a rare neurological disorder described as “terminal leukodystrophy,” causing them to lose the ability to think and behave as adults, The Telegraph reported.

After a phase of throwing temper tantrums and watching cartoons, the brothers have gradually lost the ability to talk and walk, leaving them crawling around their parents’ home, the U.K. tabloid Mirror reported…

Is it really possible for adults to revert to a childlike state? Experts in the U.S. told The Huffington Post that it is–though it occurs very rarely.