Alzheimer's Disease

Alzheimer's Disease

Alzheimer’s disease (AD) is one of the seven common multifactorial genetic inheritance disorders and is one of the most devastating brain disorders among elderly humans. It is a neurologic disorder characterized by progressive or continuous mental and social decline. AD is an undertreated and most times under-detected disease that is becoming a major public health problem. It causes the brain to shrink (atrophy) and brain cells to die. Alzheimer's disease is the most common cause of dementia — a continuous decline in thinking, behavioral and social skills that affect a person's ability to function independently.
It was determined by Alois Alzheimer in 1906 using continuous memory loss, disorientation, and pathological markers criteria. Early signs of the disease include forgetting recent events or conversations. As the disease progresses, a person with Alzheimer's disease will develop severe memory impairment and lose the ability to carry out everyday tasks.
Out of the approximately 50 million people worldwide with dementia, between 60% and 70% are approximated to have Alzheimer's disease.

Initially, the assumption was that AD was a rare condition, but later, it was considered to be an automatic consequence of aging. The stigma attached to growing old and other factors slowed down aggressive research into, and treatment of patients with AD, but these misapprehensions are waning, and treatments, though, at first moderate in effectiveness, are becoming available.

AD can be classified as early-onset or late-onset. The signs and symptoms of the early-onset form appear between a person's thirties and mid-sixties, while the late-onset form appears during or after a person's mid-sixties.
The early-onset form is much less common than the late-onset form, accounting for less than 10 percent of all cases of the disease.

The main neuropathological features of AD appear to be senile plaques and neurofibrillary tangles. The senile plaques seem to develop first in brain areas associated with cognition and spread to other cortical areas as the disease progresses. The senile plaques consist, among other components, of insoluble deposits of amyloid p-peptide (Aβ), a fragment of the amyloid precursor protein (APP).
Early-onset familial Alzheimer’s disease is inherited in an autosomal dominant pattern, which means one copy of an altered gene in each cell is sufficient to cause the disorder. In most cases, an affected person inherits the altered gene from one affected parent.
The inheritance pattern of late-onset Alzheimer’s disease is uncertain. People who inherit one copy of the apolipoprotein E (APOE) E4 allele have an increased chance of developing the disease and those who inherit two copies of the allele are at even greater risk.
Not all people with Alzheimer’s disease have the e4 allele, and not all people who have the e4 allele will develop the disease.

A recent meta-analysis of more than 14 000 patients with AD and controls showed that the APOE-4 allele represents a major risk factor for AD in both men and women from a large number of racial and ethnic groups across all ages between 40 and 90 years. The genetic risk of AD attributable to APOE-4 is estimated at 45% to 60%. It appears that APOE-4 does not act by increasing Aβ production, but by enhancing Aβ aggregation or decreasing its clearance. Another recently identified putative risk factor is lipoprotein(a), which appears to protect against late-onset AD in noncarriers and is an additional risk factor for late-onset AD in carriers of the APOE-4 allele.


References
“Alzheimer Disease: Medlineplus Genetics.” MedlinePlus, U.S. National Library of Medicine, https://medlineplus.gov/genetics/condition/alzheimer-disease/.
“Alzheimer's Disease Genetics Fact Sheet.” National Institute on Aging, U.S. Department of Health and Human Services, https://www.nia.nih.gov/health/alzheimers-disease-genetics-fact-sheet#:~:text=Early%2DOnset%20Alzheimer's%20Disease,-Early%2Donset%20Alzheimer's&text=Some%20cases%20are%20caused%20by,1%20(PSEN1)%20on%20chromosome%2014.
Bekris, Lynn M, et al. “Genetics of Alzheimer Disease.” Journal of Geriatric Psychiatry and Neurology, U.S. National Library of Medicine, Dec. 2010, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3044597/.