Final answer:
Alzheimer's disease is the most common neurodegenerative disease significantly affecting millions in the U.S., with numbers expected to rise due to an aging population.
Step-by-step explanation:
Alzheimer's disease is indeed the most common neurodegenerative disease, not just in the U.S., but globally, particularly affecting the elderly population. Contrary to the 1 million figure mentioned, the prevalence is much higher. In 2012, an estimated 5.4 million Americans were affected by Alzheimer's disease, with projections suggesting this number could rise to as many as 13 million by the year 2050. This condition is the leading cause of dementia, characterized by the presence of amyloid plaques and neurofibrillary tangles, alongside a shrinking of brain volume observed in patients. Researchers continue to explore genetic factors and other causes to find a cure for this devastating disease.