Alzheimer Disease (AD) is a progressive and fatal disease of the brain and is the most common form of dementia. The disease is characterized by progressive destruction of brain cells, resulting in serious memory, cognitive, and behavioral problems. Symptoms of AD begin slowly. Initial symptoms may be mild forgetfulness and is easily confused with age-related forgetfulness. However, as the disease progresses, the forgetfulness takes on a more serious nature, and affected people fail to recognize even close family members or caregivers, and more importantly, can forget how to perform simple daily activities. They may also have difficulties in speaking and understanding, and at times, turn aggressive and/or anxious. Patients are also prone to additional health problems, such as infections and frequent falls, mostly due to their inability to take care of themselves. Thus, affected patients need to be cared for and continuously looked after.
The most important risk factor for AD is recognized as age. Researchers have estimated that the number of affected people doubles every 5 years beyond the age of 65. In most industrialized countries, about 14% of people over 65 years of age and over 40% of people over 80 years of age are estimated to be affected with AD.
The anatomic pathology in AD is recognized as the presence of neurofibrillary tangles and senile plaques, accompanied by cerebrocortical atrophy. However, the tangles and plaques need to be present in sufficient numbers and in a characteristic distribution. A definite diagnosis of AD can only be confirmed upon autopsy of the brain tissue. Therefore, if the person is alive, only a 'probable' diagnosis of AD is possible. However, most physicians can analyse the medical history of the patient, and conduct basic medical tests, mental status evaluation, and neuropsychological tests and diagnose AD in 90% of the cases. The condition has no cure. Treatment can only be symptomatic, where certain medicines can be used to control the behavioral features of the condition. Caregivers are a very important aspect of patients' lives.
Several forms of AD have been noticed to occur in families, indicating the role of genetics in the development of the condition. The most important one is the early-onset form of AD, which occurs between the ages of 30 and 60 years. A fairly significant number of affected families worldwide have been found to carry mutations in the Presenilin-1 gene on chromosome 14. A smaller number of affected families have also been shown to carry mutations in the presenilin 2 gene on chromosome 1 or the Amyloid Precursor Protein (APP) gene on chromosome 21.
The more common version of AD, the late-onset form, does not have such a clear genetic component. It is thought that this form involves interplay of both genetic and environmental factors. The most important gene thought to be related to this form of the condition is the Apolipoprotein E (ApoE) gene. One variant of this gene, ApoE4, has been shown to be associated with an increased risk for developing AD. Interestingly, the ApoE4 variant is also a known risk factor for vascular dementia.
