Fill in the Blanks Complete the text. Alzheimer'sOnline version In this task you will complete the missing words related to Alzheimer by Santiago Manrique Mosquera 1 proteins toxic neurons connections healthy symptom seems disease disorder role brain Alzheimer's unravel dementia preclinical Alzheimer's is an irreversible , progressive brain that slowly destroys memory and thinking skills , and , eventually , the ability to carry out the simplest tasks . In most people with , symptoms first appear in their mid - 60s . Estimates vary , but experts suggest that more than 5 . 5 million Americans , most of them age 65 or older , may have caused by Alzheimer's . Scientists continue to the complex brain changes involved in the onset and progression of Alzheimer's disease . It likely that changes in the may begin a decade or more before memory and other cognitive problems appear . During this stage of Alzheimer's disease , people seem to be - free , but changes are taking place in the brain . Abnormal deposits of form amyloid plaques and tau tangles throughout the brain . Once - neurons stop functioning , lose with other , and die . Many other complex brain changes are thought to play a in Alzheimer's , too .