Digestive Problems in FAP – How Do You Deal With Them?

A majority of familial amyloid polyneuropathy (FAP) patients report problems with their digestive system. Here is some information about how FAP affects the digestive system, and tips on how to manage complications.

How does FAP affect the digestive system?

FAP is a rare genetic disorder caused by a mutation in the TTR gene. This gene encodes for the transthyretin proteins. When the gene is mutated, transthyretin proteins become misshapen and amyloid fibrils form. These fibrils accumulate in different parts of the body, such as the nerve cells, causing damage.

Damage to the autonomic nervous system, especially the enteric nervous system (ENS), can lead to the gastrointestinal (GI) symptoms that many with FAP experience. The ENS controls the secretions and motion of the GI tract. When nerve cells in the ENS are damaged due to amyloid buildup, movement within the digestive tract tends to diminish.

The most common GI symptoms in patients with FAP are early satiety (getting full very quickly), diarrhea, constipation, nausea, and vomiting. Difficulties with stomach emptying or abnormal bowel movements can cause all these symptoms. As the disease progresses and patients age, these GI symptoms can lead to malnourishment.

Managing symptoms

It is important to stop the progression of GI problems and relieve symptoms in order to improve patients’ nutrition and quality of life. Patients should inform their physicians about their GI symptoms, and will likely be asked to undergo testing.

Some medications can target the processes of TTR protein production. These include small-molecule TTR stabilizers that help to prevent TTR misfolding, like Vyndaqel, which is approved Europe but not in the U.S. There are also gene silencing approaches that could reduce the production of misfolded TTR proteins. Tegsedi is one such treatment, approved in the U.S., Europe and elsewhere for adults with FAP. Laxatives, such as polyethylene glycol (PEG), may help relieve constipation.

Dietary changes, such as eating small meals with low fiber and fat content, can help with upper digestive tract problems such as nausea and vomiting. Nutritional supplements can help keep patients from becoming malnourished, but patients should always consult with their doctor before taking a supplement. Increased fiber intake is not usually effective in relieving constipation in FAP.

A liver transplant may be considered for FAP patients at earlier stages (stage 1 and possibly 2) of this disease. The new liver can help in producing TTR proteins needed to slow new amyloid formation and prevent disease worsening. But it does not address existing amyloids, and patients will need to be on antirejection medications for the rest of their lives. These medications can make people more prone to infections.

Last updated Sept. 17, 2020

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