Werner's syndrome is one in which people age almost twice as fast as usual. Studies of the disease and of the genetics related to that disease, has identified at a cellural and biochemical level why this happens and in the process identifying one of the key mechanisms involved in aging in humans.
The results are reported in Zhang, et al., "A Werner syndrome stem cell model unveils heterochromatin alterations as a driver of human aging." Science (30 April 2015).
Basically, Werner's syndrome mutates genes responsible for a protein called WRN that governs how bundles of DNA called heterochromatin organize themselves, which causes heterochromatin to become disorganized. This phenomena is found both in Werner's syndrome sufferers and also in people without Werner's syndrome who are advanced in age.
The hope, of course, is that treatments targeting heterochromatin organization could retard or reverse the human aging process.