A genetic disease that shows some (but not all) characteristics of aging, greatly accelerated. These include osteoporosis, short stature, cataracts, and deficiency of fat tissue. Most Werner's sufferers die by the time they reach their forties.
What is most interesting about this disease is that it has been traced to mutations on one specific gene located on chromosome 8. It codes for a protein that resembles DNA helicases.
So here's the rub-- if just one broken gene can cause a complex disease with many different symptoms similar to aging... perhaps 'normal' aging itself can be traced down to just a few points of failure instead of everything failing at once, as many people seem to assume. It also makes sense that it's a helicase-- if it's involved in DNA replication, it's enough of a low-level process to cause the seemingly unrelated symptoms that are observed. If that's the case, then perhaps life-extension is something that we may yet benefit from in our own lifetimes, if we can learn enough about Werner's, progeria, Down's Syndrome, diabetes, and other diseases that serve as models for the 'normal' process of senescence.