TTR Gene

Transthyretin amyloidosis is a slowly progressive condition characterized by the buildup of abnormal deposits of a protein called amyloid (amyloidosis) in the body's organs and tissues. These protein deposits most frequently occur in the peripheral nervous system, which is made up of nerves connecting the brain and spinal cord to muscles and sensory cells that detect sensations such as touch, pain, heat, and sound. Protein deposits in these nerves result in a loss of sensation in the extremities (peripheral neuropathy). The autonomic nervous system, which controls involuntary body functions such as blood pressure, heart rate, and digestion, may also be affected by amyloidosis. In some cases, the brain and spinal cord (central nervous system) are affected. Other areas of amyloidosis include the heart, kidneys, eyes, and gastrointestinal tract. The age at which symptoms begin to develop varies widely among individuals with this condition, and is typically between ages 20 and 70.

There are three major forms of transthyretin amyloidosis, which are distinguished by their symptoms and the body systems they affect.

The neuropathic form of transthyretin amyloidosis primarily affects the peripheral and autonomic nervous systems, resulting in peripheral neuropathy and difficulty controlling bodily functions. Impairments in bodily functions can include sexual impotence, diarrhea, constipation, problems with urination, and a sharp drop in blood pressure upon standing (orthostatic hypotension). Some people experience heart and kidney problems as well. Various eye problems may occur, such as cloudiness of the clear gel that fills the eyeball (vitreous opacity), dry eyes, increased pressure in the eyes (glaucoma), or pupils with an irregular or "scalloped" appearance. Some people with this form of transthyretin amyloidosis develop carpal tunnel syndrome, which is characterized by numbness, tingling, and weakness in the hands and fingers.

The leptomeningeal form of transthyretin amyloidosis primarily affects the central nervous system. In people with this form, amyloidosis occurs in the leptomeninges, which are two thin layers of tissue that cover the brain and spinal cord. A buildup of protein in this tissue can cause stroke and bleeding in the brain, an accumulation of fluid in the brain (hydrocephalus), difficulty coordinating movements (ataxia), muscle stiffness and weakness (spastic paralysis), seizures, and loss of intellectual function (dementia). Eye problems similar to those in the neuropathic form may also occur. When people with leptomeningeal transthyretin amyloidosis have associated eye problems, they are said to have the oculoleptomeningeal form.

The cardiac form of transthyretin amyloidosis affects the heart. People with cardiac amyloidosis may have an abnormal heartbeat (arrhythmia), an enlarged heart (cardiomegaly), or orthostatic hypertension. These abnormalities can lead to progressive heart failure and death. Occasionally, people with the cardiac form of transthyretin amyloidosis have mild peripheral neuropathy.

Carpal tunnel syndrome is a disorder caused by disturbances in nerve function (neuropathy), leading to pain and numbness or tingling (paresthesia) primarily in the wrist and hand. While carpal tunnel syndrome can occur at any age, it most often affects people between the ages of 40 and 60. In more than half of cases, both hands are affected; however, the severity may vary between hands. When only one hand is affected, it is most often the hand used for writing (the dominant hand).

In carpal tunnel syndrome, the pain or paresthesia is usually felt in the wrist, the palm, and the first four fingers of the hand. These signs and symptoms often develop during sleep and are noticeable upon waking. Affected individuals typically shake their hand to get rid of the pain and numbness, a characteristic move known as the flick sign. As the condition advances, the signs and symptoms begin to occur during the day as well. Affected individuals may have difficulty performing manual tasks such as turning doorknobs, fastening buttons, or opening jars. The symptoms of carpal tunnel syndrome may be triggered by certain activities that flex or extend the wrist, such as driving, typing, or holding a telephone.

Over time, people with carpal tunnel syndrome can have muscle and nerve wasting (atrophy) in the affected hand and a reduced ability to detect sensations, which can be mistaken for an improvement of symptoms.