What is it?
Alzheimer‘s disease (AD) is an irreversible form of dementia characterised by memory loss, a progressive decline in intellectual ability, deteriorating language and speech skills, and by personality and behavioural changes that eventually interfere with daily living. According to Alzheimer's Australia there are over 320,000 people with dementia in Australia and it is predicted that this will grow to almost 900,000 by 2050. Approximately 55% of these will have Alzheimer's disease.
Although AD mimics some changes found in the brain as we age, it is not a normal part of the aging process. It causes nerve cell injury and death and is characterised by the build-up of senile plaques and neurofibrillary tangles (twisted protein fragments that clog nerve cells) in the brain. The destruction of nerve cells also decreases levels of acetylcholine and other neurotransmitters (chemicals necessary for communication between nerve cells) in the brain. Over time, AD results in decreased interaction between different areas of the brain.
Relationship with ageing
The risk of having AD and other dementias increases greatly with age. About 10% to 12% of the population will have dementia by the time they are over 65 years old, with the risk increasing to 50% for those who reach the age of 100. Most of the time AD is ‘late onset,’ beginning after the age of 65, and sporadic (does not seem to be family-related). ‘Early onset’ AD, starting before the age of 65, is more rare and more likely to be family-related. (It accounts for about 5% to 10% of all AD cases).
Alzheimer‘s disease appears to be caused by a variety of factors; although many of the factors are not yet well understood, some have a genetic component. We know that there are a few rare cases, associated with early onset Alzheimer‘s disease, where there is a clear genetic inheritance within specific families. These are families where members inherit genetic faults on chromosomes 21, 14 or 1. In these cases half of the children of the person with Alzheimer‘s disease are likely to have the genetic defect. All those who inherit the gene will go on to develop Alzheimer‘s disease.
Another gene, ApoE, has been associated with an increased susceptibility to early onset AD. This gene directs the production of apolipoprotein E, a protein that forms part of the body’s lipoproteins (such as HDL cholesterol) and is involved in lipid transportation and clearing dietary fats from the body. The ApoE gene normally exists in three forms: e2, e3 and e4. Everyone has two copies of the ApoE gene, in some combination of the three forms. ApoE e4 has been associated with an increased risk of AD.
There is a higher incidence of Alzheimer’s disease in those with Down syndrome and in families who have siblings and/or parents with AD and/or several generations of family members with AD. Researchers have been aware of a connection between Down syndrome and Alzheimer‘s disease since the 1940s. People with Down syndrome, who inherit an extra copy of chromosome 21, develop the same 'plaques' and 'tangles' in their brains as people with Alzheimer‘s disease.
Tests and treatment
There are no laboratory tests available that will positively diagnose Alzheimer’s disease. Currently, the only definite diagnosis of AD is to microscopically examine a section of the patient’s brain tissue after death. Pathologists look for senile plaques and neurofibrillary tangles characteristic of AD. Since plaque and tangle formation is also seen in normal ageing, the sample must be compared to a control sample (normal, non-AD brain tissue) from a person the same age as the patient.
However, doctors currently use a variety of tests and procedures to rule out other causes for dementia, such as anaemia, infection, disorders of the thyroid gland, or vitamin B12 deficiency, before diagnosing patients with ‘possible AD’ (meaning that the dementia could be due to another cause, such as a stroke). A hallmark of Alzheimer‘s disease is that it’s appearance is a subtle, progressive decline in function. If the onset of the patient’s problems is abrupt or happened in a step-wise fashion, then the cause is most likely something other than AD.
When a patient presents with symptoms of dementia, the doctor will evaluate his or her personal and family history (preferably of several generations); perform a physical examination; determine the age of onset, and give the patient neuropsychological tests to measure his or her memory, language skills and other cognitive functions. In some cases, computed tomography (CT) or magnetic resonance imaging (MRI) scans may be used to look for evidence of trauma, tumours or stroke that could be causing dementia and to look for brain atrophy (shrinkage, usually only seen later in the Alzheimer‘s disease progression).
It is possible to test for biomarkers in the CSF to help diagnose Alzheimer’s disease. However, this testing is not done routinely.
There is currently no prevention or cure for Alzheimer’s disease. Patients may live with AD for 1 to 25 years, but the average is 8 to 10 years. Treatment consists of attempting to slow the progression of the disease, easing symptoms, managing behavioural issues and providing the patient and carers with support and education. Early in the disease, those with AD may be able to live fairly normal lives with small amounts of assistance, such as memory aids and a structured environment. This is the time when the patient can make plans and participate in decisions about their future care.
Early diagnosis of AD may allow some people to receive moderate benefit from cholinesterase inhibitors; drugs that preserve intellectual functions by preserving the function of acetylcholine (a neurotransmitter in the brain that allows nerves and parts of the brain to communicate with each other), such as galantamine ("Reminyl"), donepezil ("Aricept") and rivastigmine ("Exelon"). Whenever possible, the patient’s other drugs will be evaluated and those that may worsen confusion, such as central nervous system depressants, antihistamines, sleeping pills and analgesics may be stopped. Later in the disease the NMDA inhibitor drug memantine may benefit some affected people and slow progression of the disease.
Throughout the progression of AD, antidepressants and other drugs may also be used in small quantities, along with environmental modification (making the home environment safer and more familiar), to moderate personality and behavioural issues such as depression, agitation, paranoia and violence, and to make the patient more comfortable.
While current research into the protective and therapeutic influences of substances, such as nonsteroidal anti-inflammatory drugs (NSAIDs), oestrogen, and antioxidants like vitamin E, is promising, these agents cannot yet be recommended. They each carry their own associated risks and side effects. Further studies are needed to determine their actual effectiveness and long-term safety.
Occasional forgetfulness is normal and should not be a cause for concern unless it significantly increases in frequency or interferes with daily living. Some of the causes of cognitive decline, besides AD, include nutritional deficiencies, such as vitamin B12 deficiency; metabolic conditions, including diabetes, electrolyte imbalance, hypertension (high blood pressure), and kidney, liver, and thyroid disorders; structural disorders like brain tumours, head injuries, normal pressure hydrocephalus, and vascular dementia; degenerative disease, including age-related cognitive decline, diffuse Lewy body disease, Huntington's chorea disease, Parkinson's disease, and Pick's disease; infectious diseases like HIV, Creutzfeldt-Jakob, meningitis, encephalitis, and syphilis; and still other causes, such as anxiety, depression, heavy metal poisoning (for example, lead poisoning), medication interactions and side effects, overmedication, and seizures.
There is no evidence at this time of any connection between Mad Cow disease and Alzheimer's disease even though the symptoms may appear similar.
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