The two brothers -- Matthew, 39, and Michael Clark, 42 -- contracted terminal leukodystrophy last year. It usually only affects newborns and despite having jobs both now behave much like toddlers, according to news reports.

Michael, an ex-Royal Air Force regiment member, is now thought to have a mental age of 10 and giggles constantly while his elder brother Matthew, a factory worker, behaves like a small child.