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Amyloidosis diseases are a group of diseases with certain characteristics in common. The main characteristic of these diseases is the presence of abnormally shaped proteins. In renal amyloidosis, malformed proteins are deposited in the kidneys, causing progressive kidney disease and kidney failure. There are more than 20 known proteins that can cause amyloidosis. Most of these are associated with rare hereditary forms of the disease.
Protein structure is an essential aspect of protein function, to the extent that an abnormally structured protein will not function in a normal fashion. All proteins have a three-dimensional structure that is dictated by chemical interactions between different amino acids in the protein chain. Amyloidosis diseases develop because of genetic mutation, a disease such as lymphoma, chronic inflammation or an environmental factor that causes one or more proteins fold incorrectly. These mutated or misfolded proteins therefore cannot function normally. In addition, as these abnormally structured proteins build up, they are deposited in the spaces between cells, forming a matrix that progressively disrupts the function of healthy organs and tissues.
Renal amyloidosis generally does not occur alone, but is a common effect in people with systemic amyloidosis. The systemic form of the disease results in the deposition of abnormal proteins in organs and tissues all over the body. When the kidneys become affected, the end result is renal failure, which can be treated only with a kidney transplant. Kidney amyloidosis often develops as part of an inherited syndrome. Familial renal amyloidosis sometimes is known as Ostertag type amyloidosis, named for Berthold Ostertag, the doctor who first characterized the disease in 1932.
All forms of hereditary renal amyloidosis are caused by mutations in a single protein. The most common type of kidney amyloidosis is called transthyretin (TTR) amyloidosis, and it occurs as a result of mutations in proteins such as lysozyme, fibrinogen or apolipoprotein. Symptoms of kidney amyloidosis develop as abnormal protein deposits grow larger and begin to disrupt kidney function. One of the most prevalent symptoms is the presence of slightly enlarged kidneys and very large amounts of protein in the urine. This protein is present because the affected kidneys are unable to filter protein out of waste water.
Renal amyloidosis usually is a systemic disease, so these symptoms are accompanied by symptoms related to abnormal function of other organs. These might include liver disease and enlargement, heart failure, nerve disease, thyroid enlargement and gastrointestinal tract problems. Systemic amyloidosis often is a fatal disease because of multiple organ involvement, but the progression of the disease and available treatments can vary depending on the protein abnormality involved. For example, when the abnormal protein is produced in the liver, progression of the disease sometimes can be halted with a successful liver transplant.