Alzheimer's Disease: Symptoms, Causes and Treatments
The dementia that occurs in the elderly is one of the most frightening and devastating neurological conditions. The most common cause for this condition is Alzheimer’s disease (AD). Each decade after 60 years of age the prevalence increases. It is estimated that by 2040, 14 million individuals in the United States will be affected.
The earliest noticeable symptoms are forgetfulness, memory loss, disorientation in time and space and difficulty with concentration, calculation and language. In some patients, severe behavioral changes and disturbances might be a symptom. As it is a progressive disease, the patient is incapable of self-care in the final stages. Thus far, no effective treatments exist and those that are affected usually die from complications.
The causes and underlying mechanisms of the brain abnormalities are not yet fully understood. But great progress is being made through genetics, biochemistry and cell biology. Researchers, through examination of microscopic brain tissue, have learned that AD patients show accumulations of a small fibrillar peptide, called a beta amyloid, in the spaces around synapses, and abnormal accumulations of a modified form of the tau protein in the cell bodies of the neurons.
Furthermore, a reduction in neurotransmitter marker levels occurs, for example in acetylcholine, monoamine and glutamate, which allow cells to communicate with each other. The damage in these neural systems, which are responsible for learning, memory and other higher cognitive abilities, is believed to be the cause of the clinical symptoms.
Recently, mutations have been identified in AD-linked genes on three chromosomes. On chromosome 21, the gene encoding the amyloid precursor protein can be found. More mutations have been identified in the presenilin 1 and 2 genes, on chromosomes 14 and 1 respectively. Apolipoprotein E (apoE), a gene on the 19th chromosome influences susceptibility in late life and exists in three form, with apoE4 clearly associated with increased risk.
At present, treatments are only available for some symptoms, such as agitation, sleep disturbances and depression. Some drugs are available to treat the cognitive symptoms in patients with mild to moderate Alzheimer’s. However, their effects are only temporarily.
Several other approaches are being tested. Mice models are being developed by introducing some of the aforementioned genes in mice. It is anticipated that these animal models will teach us a lot about the mechanisms of the condition. A final approach is using knock out genes. Through enzymes, beta and gamma secretase, cleave the amyloid peptide from the precursor and block the production of amyloid.