Amyloidosis is a group of diseases in which abnormally folded proteins build up in your organs and tissues, gradually interfering with how they work. These protein deposits, called amyloid, can accumulate in the heart, kidneys, liver, nerves, and other organs, eventually leading to organ damage or failure if untreated. It’s uncommon but not rare: in the United States alone, the most common form (AL amyloidosis) is diagnosed at a rate of roughly 17 cases per million adults per year, and that number has been climbing.
How Amyloid Proteins Form
Your body produces thousands of proteins that normally fold into precise three-dimensional shapes to do their jobs. In amyloidosis, certain proteins misfold. When a protein loses its proper shape, parts of its structure that are normally buried inside flip outward. These exposed regions are sticky, and the misfolded proteins begin clumping together into long, thread-like fibers called amyloid fibrils.
This clumping follows a two-phase pattern. First, a slow buildup phase where small clusters of misfolded proteins form a kind of seed. Once that seed reaches a critical size, it acts as a template, and new misfolded proteins rapidly latch on, growing the fibril like a chain reaction. The resulting fibrils are tough, insoluble, and the body has no efficient way to clear them. They accumulate between cells in organs and tissues, physically disrupting the organ’s architecture and poisoning cells with toxic protein fragments.
The Main Types of Amyloidosis
Amyloidosis is classified by which protein is misfolding. The type determines which organs are most at risk, how the disease behaves, and how it’s treated.
AL (Light Chain) Amyloidosis
This is the most commonly diagnosed systemic form. It starts in the bone marrow, where a small population of abnormal plasma cells (the same type of immune cell involved in multiple myeloma) begins producing defective antibody fragments called light chains. These light chains are structurally unstable and prone to misfolding. They circulate through the bloodstream and deposit as amyloid in distant organs, most often the heart, kidneys, liver, and nerves. The organ damage comes both from the physical buildup of fibrils and from the direct toxic effects of the misfolded light chains on cells. AL amyloidosis tends to be biased toward a specific type of light chain (lambda), which appears especially prone to misfolding.
ATTR (Transthyretin) Amyloidosis
In this form, the misfolding protein is transthyretin, a protein made by the liver that normally carries thyroid hormone and vitamin A in the blood. ATTR comes in two varieties. Wild-type ATTR (sometimes called senile amyloidosis) has no genetic cause. It predominantly affects men over 60 and targets the heart, causing it to stiffen. Hereditary ATTR results from an inherited gene mutation that makes the transthyretin protein less stable. It often strikes earlier in life and can affect the nerves, heart, and kidneys. The nerve involvement typically shows up as a rapidly worsening neuropathy along with problems in the autonomic nervous system, which controls things like digestion and blood pressure.
AA Amyloidosis
AA amyloidosis develops as a complication of chronic inflammatory conditions like rheumatoid arthritis, inflammatory bowel disease, or chronic infections. The culprit protein is serum amyloid A, an inflammation marker that stays elevated when the body is fighting a long-term disease. Over years, the excess protein misfolds and deposits primarily in the kidneys, liver, and spleen.
Symptoms and Organ Involvement
Amyloidosis is notoriously difficult to recognize early because its symptoms mimic many other conditions. What you feel depends entirely on where the amyloid is building up.
When the heart is involved, the walls of the heart thicken and stiffen, making it harder to pump blood effectively. This leads to shortness of breath, fatigue, and swelling in the legs and ankles. Cardiac involvement is the single biggest factor in determining how serious the disease becomes.
Kidney involvement disrupts the organ’s filtering system, often first showing up as foamy urine (from protein leaking into it) and swelling in the legs. Left unchecked, it can progress to kidney failure. Nerve damage causes numbness, tingling, or pain in the hands and feet. If the nerves controlling the gut are affected, you might experience alternating bouts of constipation and diarrhea. Damage to the nerves that regulate blood pressure can cause lightheadedness or fainting when you stand up quickly.
A few signs are more distinctive to amyloidosis specifically. Purplish bruising around the eyes (periorbital purpura) is one of the classic visual clues. An enlarged tongue that looks rippled along its edges is another. Easy bruising, skin thickening, and severe unexplained fatigue round out the picture. None of these symptoms alone proves amyloidosis, but certain combinations, especially heart failure with neuropathy or unexplained kidney disease with purpura, should raise suspicion.
How Amyloidosis Is Diagnosed
The gold standard for confirming amyloidosis is a tissue biopsy stained with a dye called Congo red. Under polarized light microscopy, amyloid fibrils stained with Congo red produce a characteristic color shift, traditionally described as “apple-green birefringence.” In practice, the colors can also appear yellow or orange depending on the optical setup. The International Society of Amyloidosis updated its diagnostic criteria to accept green, orange, or yellow birefringence as evidence of amyloid. Biopsies can be taken from the affected organ itself or from easier-to-access sites like abdominal fat or the gums.
For suspected ATTR cardiac amyloidosis specifically, a nuclear imaging scan using a bone-tracing radioactive marker has proven highly sensitive and specific. This scan can often confirm ATTR heart involvement without requiring a heart biopsy, which is a significant advantage. It reliably distinguishes ATTR deposits from AL deposits in the heart, though it works best in patients with the cardiac-dominant forms of the disease.
Once amyloid is confirmed, identifying the exact type is critical because treatments differ completely. Blood and urine tests looking for abnormal light chains help identify AL amyloidosis. Genetic testing can distinguish hereditary ATTR from the wild-type form.
Treatment by Type
Treatment strategies vary dramatically depending on which protein is causing the problem.
For AL amyloidosis, the goal is to wipe out the abnormal plasma cells in the bone marrow that are producing the toxic light chains. The current standard of care is a four-drug combination that includes a targeted antibody therapy (originally developed for multiple myeloma) paired with chemotherapy agents and a steroid. This regimen was established through the ANDROMEDA clinical trial and represents a major improvement over older treatment approaches. When the source of abnormal light chains is eliminated, organ damage can stabilize and sometimes partially reverse.
For ATTR amyloidosis, treatments take a fundamentally different approach. One strategy stabilizes the transthyretin protein so it doesn’t fall apart and misfold. Medications in this class have been available for over five years and remain the cornerstone of ATTR heart disease treatment, with a newer stabilizer recently gaining approval. The other strategy uses gene-silencing technology to stop the liver from making transthyretin altogether. These therapies, delivered as injections, break down the genetic instructions for building the protein before it’s ever produced. Several gene-silencing agents are either approved or in late-stage trials.
For AA amyloidosis, treatment focuses on controlling the underlying inflammatory disease. When the chronic inflammation is brought under control, levels of the problem protein drop, and amyloid deposits can slowly clear.
Prognosis and What Drives Outcomes
Survival with amyloidosis depends heavily on the type, which organs are affected, and how early treatment begins. Heart involvement is the most important prognostic factor across all types.
In AL amyloidosis, doctors use staging systems based on blood markers of heart stress and the level of circulating abnormal light chains to predict outcomes. In a large study of over 1,275 uniformly treated patients, overall median survival was about 82 months (nearly 7 years). But outcomes varied enormously by stage. Patients caught early, before significant heart damage, had survival times so long that the median wasn’t even reached during the study period. Those with moderate heart involvement had median survival around 3 years. Patients with the most advanced cardiac disease and the highest levels of heart stress markers faced a median survival of only about 5 months, highlighting how critical early detection is.
ATTR amyloidosis, particularly the wild-type cardiac form, generally progresses more slowly than AL amyloidosis. With the newer stabilizer and gene-silencing therapies, outcomes have improved substantially compared to even a decade ago. Hereditary ATTR can vary widely depending on the specific genetic mutation involved, with some mutations causing primarily nerve disease and others targeting the heart.
Across all forms of amyloidosis, the trend in recent years has been toward earlier recognition, better diagnostic tools that can identify the disease without invasive biopsies, and targeted therapies that address the root cause rather than just managing symptoms. The rising incidence numbers likely reflect improved awareness and detection rather than the disease itself becoming more common.