Familial amyloid polyneuropathy is a rare inherited progressive disease caused by mutations in the TTR gene. The disease is characterized by abnormal TTR protein deposits, or amyloids, around nerves and in tissues. These deposits cause damage to the nervous system and are associated with a number of symptoms.
The autonomic nervous system is part of the nervous system that controls and regulates the internal organs without conscious recognition. Autonomic neuropathy, or damage to the autonomic nervous system, is the most severe problem in FAP because it has a significant impact on patients’ daily lives. Symptoms of autonomic neuropathy commonly occur before sensory and motor nervous system symptoms become visible.
Autonomic dysfunction is more common in patients with early-onset FAP, which occurs before age 50. In late-onset FAP, which occurs after age 50, severe autonomic dysfunction is less common. The severity and onset of symptoms also depend on the type of mutation in the TTR gene.
These autonomic neuropathy symptoms commonly occur in FAP patients:
The autonomic nervous system controls blood pressure by regulating the dilation and constriction of blood vessels. Postural hypotension is a drop in blood pressure upon standing. It causes dizziness and fainting, which is associated with a high risk of injury due to falls.
The autonomic nervous system also controls the heart muscle, and autonomic neuropathy can cause an irregular heartbeat in patients with FAP.
Because the dilation of blood vessels is impaired in autonomic neuropathy, blood flow is decreased, most prominently in the extremities, causing cold hands and feet.
Decreased blood flow in the extremities makes hands and feet vulnerable to pressure ulcers.
The autonomic nervous system controls gastrointestinal (digestive) function. Constipation and diarrhea, which can occur alternatingly, are common symptoms in people with autonomic neuropathy. In severe cases, diarrhea can cause fecal incontinence. Nausea and vomiting are also common. Vomiting can be so severe that patients may become unable to retain a sufficient amount of food.
Continuous weight loss is observed as a consequence of gastrointestinal dysfunction.
Impaired bladder function
Common symptoms of bladder dysfunction are incontinence, frequent urination, and urine retention (incomplete emptying of the bladder). Urine retention increases the risk of recurrent bladder infections.
Pupils must adapt to light and darkness, which is mediated by the autonomic nervous system. Autonomic neuropathy can, therefore, cause pupillary dysfunction in patients with FAP.
The inability to sweat is a common symptom in FAP patients.
Impaired glucose tolerance
Autonomic nerves control the endocrine function of the pancreas. The pancreas secretes the hormone insulin in response to an increase in blood sugar. Insulin is necessary to get glucose into cells. When blood sugar is too low, the pancreas produces glucagon, a hormone that breaks down stored glycogen in the liver into glucose. FAP patients commonly experience a drop in blood sugar that is not adequately compensated by hormonal function.
Female sexual dysfunction is not well-studied in people with FAP, but impotence is common in male patients.
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