our report tonight from our chief science correspondent robert bazell. >> reporter: richard wanamaker, 62 years old, is suffering twice because of his military service. an initial traumatic brain injury or tbi. now, decades later, increasing memory loss. today's study looked at the medical records of almost 300,000 veterans, 55 and older, over seven years, and included wanamaker's situation is hardly unique. >> among veterans that have been exposed to tbi, they have an increase of two-fold risk during other study follow-up of dementia. >> wanamaker was awaiting deployment when a vietcong threw a bomb. >> i walked into it, along with six fellow sailors. >> reporter: he always had some memory problems after his injury. >> i would always find a shortcut, write things down. >> reporter: he eventually won an appointment, deputy undersecretary in the department of affairs. he had to give it up. >> has it gotten worse over the years? >> nine times out of ten i can't remember my password. it may happen a couple of times during the day. i get lost out mowing the lawn. i have a riding lawn mowe

robert bazell speaks to families known to carry a gene that brings on the disease. >> reporter: when there is a cure for alzheimer's disease, this family will likely have played a role. their father vince had a rare gene that brought it on at an early age. he was diagnosed in his 40s. each of his children has a 50/50 chance of carrying the gene and if they have it, there's a 50/50 chance that they pass it on to their children. >> it's something that we talk about openly. we don't want to keep it inside. >> reporter: the family has volunteered for countless medical tests and medical psychological evaluations. >> we started this back in the '70s and -- actually, late '60s. >> i'm proud of the fact that we're not just setting back and letting it control our lives. >> reporter: already there is a discovery out today with one study with huge implications for drug development. >> brain changes that ultimately result in alzheimer's dementia occur 15 to 20 years before there are any signs of symptoms of dedementia. >> reporter: the family constantly faces crucial decisions. >> each of you ha

it's our "making a difference" report and here's the story from nbc's robert bazell. >> reporter: dr.raim engelman keeps regular hours for arthritis patients at the university of california san francisco. he directs the rosalind russell medical research center for arthritis and frequently meets with colleagues to discuss research. >> your hands look pretty good. >> reporter: none of that would be unusual except that dr. engelman just celebrated his 100th birthday and has no plans to slow down. would you ever consider retiring? >> no. not unless i have to. >> reporter: it would be difficult to exaggerate the changes in medicine in the course of his 75-year career. >> the treatment for arthritis was aspirin. people would come in wheelchairs and gurneys. we don't see that anymore. people walk in. they're not necessarily cured, but they're much better. >> reporter: his advice for achieving longevity is not exactly the wisdom. >> i think exercise is mostly overrated. and totally unnecessary. and the use of vitamins, forget it. and i don't encourage a lot of doctors. >> reporter: so what do