Familial amyloid polyneuropathy (FAP) is a genetic disease caused by the abnormal deposits of transthyretin (TTR) proteins or amyloids around peripheral nerves and other tissues.
There are currently no approved therapies that can reverse the process of TTR amyloid fibrils formation. However, there are certain treatments that can help manage the symptoms of the disease and slow down the progression of TTR amyloid deposition, preventing complications.
Liver transplant
Almost all the TTR amyloid fibrils in the bloodstream are made in the liver and form amyloid deposits everywhere in the body except in the eye and the blood vessels around the brain.
A liver transplant is therefore considered the first-line intervention for patients with defective TTR proteins. The patient’s liver, which makes abnormal TTR proteins, is removed and replaced by a donor’s liver which produces normal TTR. The goal is to prevent the formation of further amyloid deposits.
Liver transplant therapy presents higher success outcomes when performed in patients with the TTR Val30Met mutation, the most common type of FAP-causing mutation. Likewise, performing the surgery at a young age and early in the disease course before the heart or nerves sustain too much damage can also lead to a positive outcome.
Amyloid deposits sometimes continue to be formed and the process may even be accelerated after the transplant procedure. It is thought that the existing abnormal TTR amyloid deposits act as a template encouraging normal wild type TTR from the donor’s liver to also form TTR amyloid fibrils, leading to a continuous accumulation of TTR amyloid. This problem arises most often in older patients with mutations other than TTR Val30Met.
Symptoms management
The management of symptoms associated with peripheral neuropathy and autonomic dysfunction should be initiated immediately following diagnosis. Symptomatic treatment may include painkillers, anti-diarrhea drugs, and drugs to treat drops in blood pressure and faintness that happen when standing up from a sitting or lying-down position.
There are also a number of experimental treatments currently being evaluated in clinical trials for FAP.
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