- By Terri Malloy
Expert Alert: Cardiac amyloidosis masquerades as other conditions; 1 type affects more black Americans
ROCHESTER, Minn. ― Human bodies constantly produce thousands of perfectly folded proteins, but some proteins get misfolded. An excess of these misfolded proteins can overwhelm the body's ability to remove them. When that happens, the rogue proteins bind together and form a substance called amyloid. Webs of amyloid can deposit in any tissue or organ, but some types affect the heart.
Martha Grogan, M.D., a Mayo Clinic cardiologist and director of the Cardiac Amyloid Clinic at Mayo Clinic in Rochester, says the treatment approach depends on two important factors: early diagnosis and knowing which type of amyloid a person has.
Three types of amyloid can affect the human heart:
- Light chain amyloid
This type progresses quickly and has the worst prognosis. It is produced in the bone marrow and can be deposited in any tissue or organ. This type of amyloid causes organ failure or neurological damage. Treatment may include chemotherapy or stem cell transplant with a patient's own cells.
- Wild type transthyretin amyloid
This type originates in the liver and becomes unstable. It typically shows up in men over age 60. Carpal tunnel syndrome or spinal stenosis is common, often occurring six to 10 years before wild type transthyretin is diagnosed. New medication options are available to stabilize protein or prevent protein folding.
- Hereditary type transthyretin amyloid
This type originates in the liver. It is caused by mutations of the transthyretin gene. A single copy of the gene variation is enough to cause the condition. Effects vary. Not everyone with the gene variation gets amyloidosis. This type is rare, except in black Americans. Treatment can include a liver or heart transplant. New medication options are available to prevent the protein from being produced, or to stabilize protein and prevent misfolding.
Each type causes irreversible thickening of the heart muscle and can lead to congestive heart failure. But each of these cardiac amyloid types has distinct differences. For example, people of African or Caribbean descent are at increased risk of hereditary type transthyretin amyloid.
Dr. Grogan says amyloidosis is tricky to diagnose because layers of amyloid build up over time. At first, there are no symptoms. Later, the symptoms often imitate other conditions. A health care provider may suspect cardiac amyloidosis if a patient's echocardiogram or MRI shows certain heart characteristics, such as thickened walls, abnormal strain and restricted filling of blood. A patient may have unexplained heart failure, stroke or atrial arrhythmia that can be traced back to amyloid. Kidney disease, an unexplained rise in lipids and signs of neural damage also may be present.
"When cardiac amyloid is suspected, the first thing is to find out what type it is because that will guide treatment. There is no medication available at this time that has been proven to take amyloid out of the heart, but we can stop more amyloid from being produced by treating the underlying protein problem," says Dr. Grogan.
Using a tissue biopsy taken from the fat, bone marrow, kidney or heart, a pathologist uses a technique called mass spectrometryto examine the tissue and determine the type of amyloid. If light chain amyloid is ruled out by blood and urine tests, then a biopsy is not always needed. In this setting, a pyrophosphate scan may be used to see if transthyretin amyloid is present in the heart. If the patient has transthyretin type, the next step is genetic testing to see if there is an inherited variation that is causing the amyloid.
"The hereditary form of transthyretin amyloid is generally rare. However, we know that approximately 4% of the black population in the U.S. carries the gene. Not all of these people develop amyloidosis, but this is a huge population at risk," says Dr. Grogan.
To interview Dr. Grogan, contact firstname.lastname@example.org.
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- Terri Malloy, Mayo Clinic Public Affairs, 507-284-5005, email@example.com