New player implicated in Alzheimer's and other dementias

Why do neurodegenerative diseases such as Alzheimer’s affect only the elderly? Why do some people live to be over 100 with intact cognitive function while others develop dementia decades earlier?More than a century of research into the causes of dementia has focused on the clumps and tangles of abnormal proteins that appear in the brains of people with neurodegenerative diseases.