By the looks of their home, Tony and Christine Clark are raising two rambunctious 7-year-old boys. Model train tracks and Monopoly pieces are scattered on tables and cartoons flicker on the TV set.

But the Clarks' two sons are grown men who share only the same interests and emotional fluctuations of little boys. Like the character portrayed by Brad Pitt in the 2008 film "The Curious Case of Benjamin Buttons," Matthew, 39, and Michael, 42, are aging backwards.

Diagnosed with a terminal form of leukodystrophy, one of a group of extremely rare genetic disorders that attack the Myelin, or white matter, in the nervous system, spinal cord, and brain. In the Clarks' case, the condition has not only eroded their physical capacities, but their emotional and mental states as well.
Only six years ago