Alzheimer's disease

Meaning: Alzheimer's disease is a progressive neurodegenerative disorder and a leading cause of dementia, a decline in memory, language, judgment and daily function beyond normal aging. Brain tissue shows beta-amyloid plaques outside neurons and neurofibrillary tangles of tau protein inside them. Acetylcholine levels fall and the hippocampus is damaged early, so forming new explicit memories fails first (anterograde amnesia). Older memories fade later, and procedural memory tends to be preserved longer.

On the MCAT: A passage describes an older patient who repeats questions, forgets recent events and gets lost. You identify the structure involved (hippocampus), the memory type lost first (new explicit memory), the type spared longer (procedural), or the neurotransmitter that is reduced (acetylcholine). Age is the main risk factor, and a biochemistry passage may use the plaques as an example of protein misfolding and aggregation.

Common confusion: Students equate it with Parkinson's disease, which involves loss of dopamine neurons in the substantia nigra and mainly motor symptoms such as tremor and rigidity. Alzheimer's is chiefly cognitive. Also, dementia is the syndrome and Alzheimer's is one cause of it, so the two terms are not synonyms.