Amyloidosis refers to the accumulation of proteins called amyloid in the tissues of the body. Although the proteins do not interfere with any chemical reactions, they physically hamper the normal functions of cells. In Alzheimer's disease, a localized form of amyloidosis occurs as beta amyloid protein builds up in the brain as part of an extensive network of deposits called plaques.
Beta Amyloid Protein
In the brains of patients with Alzheimer's disease, plaques form that consist of an abnormal protein fragment-called a beta-protein fragment-of a precursor to the beta-amyloid protein. The beta fragment sometimes associates with apolipoprotein E, which can alter how the plaques accumulate. Genetic mutations that alter the way the body processes the amyloid precursor protein cause an early-onset form of Alzheimer's, and alterations in the gene encoding apoplipoprotein E can increase the risk of Alzheimer's disease or protect against it, depending on the nature of the changes and how they affect the deposit of beta-protein.
Role
Alzheimer's disease eventually kills brain cells. The role of the beta-amyloid deposits in Alzheimer's disease is not clear. Doctors do not know if the abnormal protein deposits cause the symptoms or merely correlate with them, but MayoClinic.com says that evidence favors the hypothesis that the beta-amyloid proteins might be the cause of cellular death. In any case, the clumpy plaques interfere with the normal connections and communications between the nerve cells of the brain in people with Alzheimer's disease.
Sites
In Alzheimer's disease, beta-amyloid proteins accumulate in the cerebral cortex, the surface layer of the brain area critical for memory, language, and analytical thinking, and in the neurons in the tissue layer just below the cortex. According to MayoClinic.com the abnormal protein deposits can also build up around the blood vessels in the cerebral lobe of the brain, causing a cerebral hemorrhage, or bleeding into the brain.
Diagnosis
Using memory and thinking tests and ruling out other possible cause of dementia with blood tests or images of the brain, doctors can accurately diagnose about 90 percent of all cases of Alzheimer's disease, says MayoClinic.com. A definite confirmation of the diagnosis, however, requires testing of the brain cells under a microscope after death to verify the presence of the beta-protein plaques.
Treatments
The current treatments for Alzheimer's disease do not target the build-up of beta-protein, but instead they aim to improve behavioral symptoms of the disease, or slow its course, by targeting signals that might be malfunctioning due to the presence of plaques. Cholinesterase inhibitors such as donepezil and galantamine work by increasing the level of nerve signaling chemicals in the brain, while memantine protects vulnerable brain cells from the damaging effects of a chemical signal called glutamate.
