Alzheimers disease in people with down syndrome many but not all people with down syndrome develop alzheimers disease when they get older people with down syndrome are born with an extra copy of chromosome 21 which carries a gene that produces a specific protein called amyloid precursor protein app. As with all adults advancing age also increases the chances a person with down syndrome will develop alzheimers disease according to the national down syndrome society about 30 of people with down syndrome who are in their 50s have alzheimers dementia about 50 of people with down syndrome in their 60s have alzheimers dementia. Alzheimers disease is not inevitable in people with downs syndrome while all people with downs syndrome are at risk many adults with downs syndrome will not manifest the changes of alzheimers disease in their lifetime although risk increases with each decade of life at no point does it come close to reaching 100. In the united states estimates indicate there are between 250000 and 400000 individuals with down syndrome ds and nearly all will develop alzheimers disease ad pathology starting in their 30s with the current lifespan being 55 to 60 years approximately 70 will develop dementia and if th