Alzheimer Disease Health Article

Definition

Alzheimer disease is a neurological disorder characterized by slow, progressive memory loss due to a gradual loss of brain cells. Alzheimer disease significantly affects cognitive (thought) capabilities and, eventually, affected individuals become incapacitated. Alzheimer-related issues can cause emotional and financial upheaval for both the individuals with the disease and their families. Alzheimer disease is the most common form of dementia (loss of intellectual function) and, according to the National Institutes of Health (NIH), it is the fourth leading cause of death in adults.

Description

The condition was first described in 1906 by Alois Alzheimer, a German physician. Alzheimer characterized two abnormal structures in the brain of a woman with dementia that are now considered the hallmarks of the disease: amyloid plaques and neurofibrillary tangles. The nature of Alzheimer disease is progressive. Initially, dementia is manifested by barely noticeable memory deficits. Eventually, the memory loss becomes more severe until it is incapacitating. Other symptoms such as confusion, the inability to articulate words correctly, and hallucinations occur with varying degrees. Emotional problems such as easy agitation, poor judgment, and feelings of withdrawal are also common in the early stages. Affected individuals are also likely to develop seizures, hypertonicity (increased muscle movements), and incontinence. Without treatment or supervision, death often results from malnutrition or pneumonia. From the initial symptoms, disease progression can last up to 25 years, although typically the duration ranges from eight to 10 years.

Demographics

Dementia is thought to affect between 25–50% of individuals 85 years or older. The risk of developing Alzheimer disease increases with age and is independent of sex or geographical location (although there are environmental toxic agents that can impair various cognitive functions, including memory loss). A genetic association has been found for higher risk of developing Alzheimer disease in individuals with mutations in a particular gene who are also African American or Caribbean Hispanics. This association is greatest in individuals with a positive family history of dementia.

Approximately 10% of people 65 years or older are at risk for developing significant memory loss. More than half of these individuals (5% of all individuals 65 years or older) have Alzheimer disease. Approximately four in 10,000 individuals between the ages of 40 and 60 are at risk for having Alzheimer disease.

Causes and symptoms

Although there are several known causes of Alzheimer disease, about 75% of cases are sporadic and occur without a clear cause; this percentage represents people without a family history of the disorder. Scientists assume that these cases are due to a combination of unknown genetic predisposing factors and environmental exposures. Although various narcotics, therapeutic drugs, viruses, and toxins have been implicated in the etiology of the disease, there is currently no proof that they can cause Alzheimer disease.

Genetic basis for Alzheimer disease

Of all persons with Alzheimer disease, up to 25% of cases are thought to be part of a familial-based inheritance pattern and therefore are only determined based on family history or genetic test results. In general, these forms of Alzheimer disease are inherited as an autosomal dominant disorder, meaning that affected individuals have a 50% chance of passing on the mutated gene to their offspring in each pregnancy. There is a late-onset familial form (AD2), three early-onset familial forms (AD1, AD3, AD4), and a form of Alzheimer disease associated with Down syndrome.

Down syndrome and Alzheimer disease

Less than 1% of all cases of Alzheimer disease are due to a chromosomal defect called trisomy 21 (also known as Down syndrome). This occurs when there are three copies of genes found on chromosome 21, usually due to a person having an extra chromosome 21. These individuals usually develop Alzheimer disease after the age of 40. The APP gene, which encodes the amyloid precursor protein and is implicated in the pathogenesis of Alzheimer disease, is localized to chromosome 21; it is felt that people with Down syndrome overproduce this protein, resulting in its accumulation in the brain. The excess protein is thought to cause the disease.