Alzheimer's disease (AD) is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death. It was first described by German psychiatrist and neuropathologist Alois Alzheimer in 1906 and was named after him. Most often, AD is diagnosed in people over 65 years of age, although the less-prevalent early-onset Alzheimer's can occur much earlier. In 2006, there were 26.6 million sufferers worldwide. Alzheimer's is predicted to affect 1 in 85 people globally by 2050.

Although Alzheimer's disease develops differently for every individual, there are many common symptoms. Early symptoms are often mistakenly thought to be 'age-related' concerns, or manifestations of stress. In the early stages, the most common symptom is difficulty in remembering recent events. When AD is suspected, the diagnosis is usually confirmed with tests that evaluate behaviour and thinking abilities, often followed by a brain scan if available, however, examination of brain tissue is required for a definitive diagnosis. As the disease advances, symptoms can include confusion, irritability, aggression, mood swings, trouble with language, and long-term memory loss. As the sufferer declines they often withdraw from family and society. Gradually, bodily functions are lost, ultimately leading to death. Since the disease is different for each individual, predicting how it will affect the person is difficult. AD develops for an unknown and variable amount of time before becoming fully apparent, and it can progress undiagnosed for years. On average, the life expectancy following diagnosis is approximately seven years. Fewer than three percent of individuals live more than fourteen years after diagnosis.

The cause and progression of Alzheimer's disease are not well understood. Research indicates that the disease is associated with plaques and tangles in the brain. Current treatments only help with the symptoms of the disease. There are no available treatments that stop or reverse the progression of the disease. As of 2012, more than 1,000 clinical trials have been or are being conducted to test various compounds in AD. Mental stimulation, exercise, and a balanced diet have been suggested as ways to delay cognitive symptoms (though not brain pathology) in healthy older individuals, but there is no conclusive evidence supporting an effect.

Because AD cannot be cured and is degenerative, the sufferer relies on others for assistance. The role of the main caregiver is often taken by the spouse or a close relative. Alzheimer's disease is known for placing a great burden on caregivers; the pressures can be wide-ranging, involving social, psychological, physical, and economic elements of the caregiver's life. In developed countries, AD is one of the most costly diseases to society.

Causes

The cause for most Alzheimer's cases is still mostly unknown except for 1% to 5% of cases where genetic differences have been identified. Several competing hypotheses exist trying to explain the cause of the disease:

Cholinergic hypothesis: The oldest, on which most currently available drug therapies are based, is the cholinergic hypothesis, which proposes that AD is caused by reduced synthesis of the neurotransmitter acetylcholine. The cholinergic hypothesis has not maintained widespread support, largely because medications intended to treat acetylcholine deficiency have not been very effective.

Amyloid hypothesis: The amyloid hypothesis postulates that extracellular beta-amyloid (Aβ) deposits are the fundamental cause of the disease. The theory holds that an amyloid-related mechanism that prunes neuronal connections in the brain may be triggered by ageing-related processes in later life to cause the neuronal withering of Alzheimer's disease.

Genetics: Mutations in the TREM2 gene have been associated with a 3 to 5 times higher risk of developing Alzheimer's disease. A suggested mechanism of action is that when TREM2 is mutated, white blood cells in the brain are no longer able to control the amount of beta amyloid present.

Tau hypothesis: The tau hypothesis is the idea that tau protein abnormalities initiate the disease cascade. In this model, the tau protein triggers neurofibrillary tangles inside nerve cell bodies. When this occurs, the microtubules disintegrate, collapsing the neuron's transport system. This may result first in malfunctions in biochemical communication between neurons and later in the death of the cells.

Prevention

At present, there is no definitive evidence to support that any particular measure is effective in preventing AD. Global studies of measures to prevent or delay the onset of AD have often produced inconsistent results. Epidemiological studies have proposed relationships between certain modifiable factors, such as diet, cardiovascular risk, pharmaceutical products, or intellectual activities among others, and a population's likelihood of developing AD. Only further research, including clinical trials, will reveal whether these factors can help to prevent AD.

Treatment

There is no cure for Alzheimer's disease; available treatments offer relatively small symptomatic benefit but remain palliative (relieving and preventing the suffering of patients) in nature. Current treatments can be divided into pharmaceutical, psychosocial and caregiving.

Epidemiology

Regarding incidence, studies provide rates between 10 and 15 per thousand person–years for all dementias and 5–8 for AD, which means that half of new dementia cases each year are AD. Advancing age is a primary risk factor for the disease and incidence rates are not equal for all ages: every five years after the age of 65, the risk of acquiring the disease approximately doubles, increasing from 3 to as much as 69 per thousand person years. There are also sex differences in the incidence rates, women having a higher risk of developing AD particularly in the population older than 85. The risk of dying from Alzheimer’s disease is twenty-six percent higher among the non-Hispanic white population than among the non-Hispanic black population, whereas the Hispanic population has a thirty percent lower risk than the non-Hispanic white population.

Notable Cases

As Alzheimer's disease is highly prevalent, many notable people have developed it. Well-known examples are former United States President Ronald Reagan and Irish writer Iris Murdoch, both of whom were the subjects of scientific articles examining how their cognitive capacities deteriorated with the disease. Other cases include the retired footballer Ferenc Puskás, the former Prime Ministers Harold Wilson (United Kingdom) and Adolfo Suárez (Spain), the actress Rita Hayworth, the actor Charlton Heston, the novelist Terry Pratchett, Indian politician George Fernandes, and the 2009 Nobel Prize in Physics recipient Charles K. Kao.

History

The ancient Greek and Roman philosophers and physicians associated old age with increasing dementia. It was not until 1901 that German psychiatrist Alois Alzheimer identified the first case of what became known as Alzheimer's disease in a fifty-year-old woman he called Auguste D. He followed her case until she died in 1906, when he first reported publicly on it. During the next five years, eleven similar cases were reported in the medical literature, some of them already using the term Alzheimer's disease. The disease was first described as a distinctive disease by Emil Kraepelin. He included Alzheimer's disease, also named presenile dementia by Kraepelin, as a subtype of senile dementia in the eighth edition of his Textbook of Psychiatry, published in 1910.

Source and more information:
Wikipedia article Alzheimer's disease

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