Alzheimer's disease
In 1901, a German psychiatrist named Alois Alzheimer examined a fifty-year-old woman he called Auguste D. Her symptoms included memory loss, hallucinations, and delusions that confused her family and doctors. She died in 1906, and Alzheimer published his findings on her case that same year. This marked the first recorded instance of what would become known as Alzheimer's disease. For decades, the condition was reserved for people between ages 45 and 65 who developed dementia-like symptoms. The terminology changed after 1977 when medical experts concluded that presenile and senile dementias shared identical clinical features. They eventually adopted the name Alzheimer's disease to describe individuals of all ages with this specific pattern of decline.
The course of Alzheimer's disease generally follows three distinct stages: early or mild, middle or moderate, and late or severe. In the initial phase, short-term memory loss appears as difficulty remembering recently learned facts. People may struggle with complex activities like planning or abstract thinking while retaining older memories. Language problems emerge as vocabulary shrinks and word fluency decreases. By the middle stage, speech difficulties worsen due to frequent incorrect word substitutions. Reading and writing skills fade, and motor coordination declines, increasing fall risks. Behavioral changes such as wandering, irritability, and emotional outbursts become common during this period. Approximately 30% of patients develop delusional misidentifications where they believe strangers are intruders in their homes. The final stage brings complete dependence on caregivers. Language reduces to simple phrases or single words before total loss occurs. Muscle mass deteriorates until bedridden status prevents self-feeding. Death usually results from external factors like pneumonia rather than the disease itself.
Abnormal amounts of amyloid beta protein accumulate extracellularly as dense plaques outside neurons. Tau proteins form neurofibrillary tangles inside cells by becoming hyperphosphorylated. These two misfolded proteins share features that promote disease progression through prion-like seeding mechanisms. The amyloid hypothesis suggests that accumulation of abnormal Aβ triggers a cascade leading to tauopathy and eventual degeneration. Evidence supports Aβ playing a central role because all autosomal dominant genetic causes affect either APP or enzymes generating Aβ. People with Down syndrome who carry an extra copy of the APP gene almost universally develop Alzheimer's symptoms by age 40. Conversely, rare mutations reducing Aβ production protect against the disease. Microglia serve as principal immunological cells recognizing and taking up Aβ through pattern recognition receptors. However, these same cells can become sources of pro-inflammatory mediators deleterious to neurological function. Inflammation acts as both secondary response to tissue damage and marker of immune system activity within the brain.
The strongest genetic risk factor for sporadic Alzheimer's disease is the APOEε4 allele. Between 40% and 80% of patients possess at least one copy of this specific apolipoprotein E variant. Heterozygotes carrying one copy face three times higher risk while homozygotes with two copies face fifteen times greater danger. Only 1, 2% of cases involve inherited autosomal dominant mutations causing early-onset familial Alzheimer's disease. These familial forms tend to progress more rapidly than typical late-onset cases. Mutations in genes encoding amyloid-beta precursor protein (APP) and presenilins PSEN1 and PSEN2 drive most familial instances. Less than 5% of sporadic cases show earlier onset despite being polygenic disorders. Alleles in the TREM2 gene have been linked to three to five times higher risk of developing the condition. Nigerian Yoruba people do not exhibit the relationship between APOEε4 dosage and incidence seen in other populations. Early-onset familial Alzheimer's disease can be attributed to deletions like codon 693 of APP known as the Osaka mutation found in Japanese pedigrees.
Alzheimer's disease can only be definitively diagnosed through autopsy findings examining brain tissue histologically for plaques and tangles. Clinical diagnoses remain possible or probable based on medical history, behavioral observations, and neuropsychological testing. Advanced imaging techniques include computed tomography scans, magnetic resonance imaging, single-photon emission computed tomography, and positron emission tomography. FDG-PET scans sometimes reveal bilateral asymmetric temporal and parietal reduced activity when standard tests prove unclear. FDA-approved radiopharmaceutical diagnostic agents used in PET include florbetapir approved in 2012 and flortaucipir approved in 2020. Cognitive assessments such as the mini-mental state examination help characterize disease states but lack sensitivity for mild cognitive impairment. In May 2025, the US FDA approved a blood test by Fujirebio Diagnostics' Lumipulse G device for early detection of amyloid plaques associated with AD in adults aged 55 years and older showing symptoms. Up to 23% of clinically diagnosed cases may be misdiagnosed with pathology suggesting another condition mimicking Alzheimer's features.
No treatments stop or reverse progression though some temporarily improve symptoms. Four acetylcholinesterase inhibitors including tacrine, rivastigmine, galantamine, and donepezil treat mild to severe stages. Memantine serves as an NMDA receptor antagonist intended for moderate or advanced disease phases. Benefit from these medications remains small despite evidence supporting medical efficacy in certain groups. Common side effects involve nausea and vomiting occurring in approximately 10, 20% of users due to cholinergic excess. Less frequent secondary effects include muscle cramps, decreased heart rate, reduced appetite, weight loss, and increased gastric acid production. Atypical antipsychotics modestly reduce aggression and psychosis but carry serious adverse risks like stroke or movement difficulties. Two monoclonal antibodies targeting amyloid beta, donanemab and lecanemab, have been approved in the US as of 2024. Lecanemab carries a boxed warning about amyloid-related imaging abnormalities yet was approved for sale in Japan, South Korea, China, Hong Kong, and Israel by early August 2024.
As of 2020, approximately 50 million people worldwide suffered from Alzheimer's disease. It most often begins in individuals over 65 years old though up to 10% of cases affect those aged 30s to mid-60s. About 6% of people aged 65 and older develop the condition with women affected more frequently than men. Every five years after age 65, risk doubles increasing from 3 to as much as 69 per thousand person-years. In the United States during 2020, prevalence reached 5.3% for ages 60, 74 rising to 13.8% for 74, 84 and 34.6% beyond 85. Prevalence rates are estimated to triple by 2050 reaching 152 million compared to current figures. Women show higher lifetime risk even when adjusted for age according to studies like the Framingham study finding nearly twice the risk compared to men. Tau protein accumulates faster in females while APOE4 increases AD risk more significantly among them despite equal pathology amounts observed.
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Common questions
When was Alzheimer's disease first recorded and by whom?
Alois Alzheimer examined Auguste D in 1901 and published his findings on her case that same year. This marked the first recorded instance of what would become known as Alzheimer's disease.
What are the three stages of Alzheimer's disease progression?
The course of Alzheimer's disease generally follows three distinct stages: early or mild, middle or moderate, and late or severe. The final stage brings complete dependence on caregivers before death usually results from external factors like pneumonia rather than the disease itself.
Which genetic variant is the strongest risk factor for sporadic Alzheimer's disease?
The strongest genetic risk factor for sporadic Alzheimer's disease is the APOEε4 allele. Between 40% and 80% of patients possess at least one copy of this specific apolipoprotein E variant.
How can Alzheimer's disease be definitively diagnosed?
Alzheimer's disease can only be definitively diagnosed through autopsy findings examining brain tissue histologically for plaques and tangles. Clinical diagnoses remain possible or probable based on medical history, behavioral observations, and neuropsychological testing.
When was the blood test by Fujirebio Diagnostics approved for early detection of amyloid plaques?
In May 2025, the US FDA approved a blood test by Fujirebio Diagnostics' Lumipulse G device for early detection of amyloid plaques associated with AD in adults aged 55 years and older showing symptoms.