Familial Amyloid Cardiomyopathy

Causes

Both FAP and FAC are caused by inherited alterations in the TTR gene. The genes in the nucleus of each cell of our bodies act like a blueprint or a recipe for building the proteins which make up the entire human body. Gene alterations lead to alterations in the construction of body proteins, just like alterations in the blueprint for building a house will lead the builders to alter the structure of the house.

The inherited TTR gene alterations that cause FAP and FAC are called mutations. People born with these inherited mutations produce abnormal, variant TTR protein all of their lives. Over 100 different mutations in the TTR gene have been observed, most of which cause production of variant TTR with a tendency to misfold into amyloid fibrils, which then form TTR amyloid deposits in the tissues, mainly in the nerves and heart, sometimes in the eyes and rarely in the kidneys, thyroid, adrenals and blood vessels.

Amyloid deposits tend to build up slowly, over the course of many years, so organ damage accumulates slowly, leading to the symptoms of FAP or FAC which can appear at any time from early adult life to old age.

Symptoms of FAP tend to present earlier than symptoms of FAC, but there is still much variability. For example, in Portugal, FAP commonly presents up to 25 years earlier than it does in Sweden although the mutation Val30Met is the same. Very rarely, young adults may develop FAC, but FAC is far more common in elderly people. The most common FAC mutation (Val122Ile) is most frequent in men of African ethnic origin over the age of 60 years.

The clinical symptoms of FAC are very similar to those of senile systemic amyloidosis (SSA), which is caused by amyloid deposits made of normal wild type TTR in people without mutations in the TTR gene.

FAC, FAP and SSA are compared in more detail in this Table.

Inheritance

FAP and FAC are inherited in a manner known as ‘autosomal dominant’. This means that the condition may be passed down to children either from the mother or from the father. Only one copy of the mutated gene is sufficient to cause the disease.

As shown in the Figure here, an affected parent has a 50% chance of passing on the mutated gene to each child. Girls and boys have an equal chance of inheriting the mutated gene. Any children who receive the mutated gene then also have a 50% chance of passing it on to each of their children. Children of an affected parent who did NOT inherit a mutated gene cannot pass the condition on to their own children. Brothers and sisters of a patient with FAP or FAC have a 50% chance of having the mutated gene.

The situation is further complicated by an additional factor known as ‘incomplete penetrance’. This means that inheritance of a TTR gene mutation does not always lead to symptoms of FAP or FAC. Some people inherit a TTR gene mutation but do not develop any TTR amyloid deposits, while others develop small TTR deposits but no symptoms. FAP is equally common in men and women. FAC that is caused by the Val122Ile mutation is more common in men than in women although girls and boys have an equal chance of inheriting the Val122Ile mutation. Many people carry a TTR mutation all their lives but do not develop TTR amyloidosis. The reason for this is unclear.

Sometimes a patient diagnosed with FAP or FAC may be unaware of any other affected family members. This may be because other family members did not develop disease despite carrying the mutation. Alternatively, the mutation may have arisen for the first time in that patient, or other affected family members may have not been correctly diagnosed, or may have died of other causes before reaching the age when they would have developed symptoms.

Healthy family members of patients with FAP or FAC may be concerned about their own risk of developing the disease. Risk assessment can be complicated, and a doctor with expertise in amyloidosis should be consulted. In order to give personalized genetic counselling regarding the likelihood that someone with the TTR mutation will actually develop FAP or FAC, doctors will require information on family health history in addition to genetic testing for TTR mutations. Genetic testing of healthy people can identify mutations in the TTR Val122Ile gene but cannot predict whether or not the person will develop FAC, FAP or both.

Symptoms & Signs

The symptoms of FAP and FAC are described in the table below.

In FAP, symptoms are usually first detected after age 30, but sometimes can occur as early as age 20 or as late as age 80.

Symptoms of FAC usually appear after age 50. If there are small TTR amyloid deposits in the heart, they may cause no symptoms at all. When the deposits are large, they can cause symptoms of heart disease like those described in the table below. Carpal tunnel syndrome (pain and tingling in the wrists and hands) often appears several years before heart disease. It may be caused by TTR amyloid deposits in the wrists.

Organ affected by TTR amyloid deposits	Symptoms
Nerve disease (neuropathy) affecting: peripheral nerves (control sensation and movement in the arms and legs) autonomic nerves (control automatic body functions like blood pressure, digestive system, sexual function)	Peripheral neuropathy: numbness, tingling, pins and needles in the feet and hands weakness and pain in the arms and legs loss of sensation
	Autonomic neuropathy: postural hypotension (blood pressure drops on standing leading to dizziness or fainting) disturbed bowel function – alternating diarrhea and constipation, nausea, vomiting urinary retention impotence reduced sweating
Heart disease (restrictive cardiomyopathy): amyloid deposits in the heart cause stiffening and thickening of the heart muscle, so the heart cannot pump the blood around the body as efficiently as usual.	Heart failure: shortness of breath, sometimes just after mild exertion, sometimes when lying flat palpitations due to abnormal heart rhythms, most frequently atrial fibrillation or atrial flutter ankle swelling (edema) fatigue, nausea, weight loss dizziness and fainting, may occur after exertion, or after eating disrupted sleep angina (chest pain)
Sometimes: Eye Rarely: Kidneys Thyroid gland Adrenal glands Blood vessels	Local symptoms related to the organ affected: blurred vision, blindness, protein loss in the urine, kidney failure, goiter (thyroid swelling), etc.

Different TTR gene mutations and different types of FAP and FAC

More than 100 different TTR gene mutations have been reported in the medical literature.  The disease spectrum is wide and different mutations have been associated with different disease courses resulting in considerable variability in the type and severity of symptoms.  The same mutation can cause different clinical features in different families, and even within the same family.  For example, some mutations cause mostly neuropathy, while others cause mostly heart disease, and others cause equal amounts of both. Some mutations seem to cause severe, early onset disease in all affected family members, while others cause quite mild, late onset disease.

In patients from Portugal and Japan with the Val30Met mutation (the most common FAP-causing mutation), symptoms of neuropathy usually appear after age 30, while patients from Sweden with the Val30Met mutation often develop neuropathy after age 50. Heart disease is less common with the Val30Met mutation than with other mutations.  In contrast, patients with Val122lle typically present only with FAC and have little involvement of the peripheral nerves.

The Thr60Ala mutation is most common in people with Irish ancestry, and they usually develop both neuropathy and heart disease.

The presence of a TTR gene mutation known to cause TTR amyloidosis does not necessarily mean that symptoms will develop. There have been case reports of people over 60 years of age with two copies of the TTR gene mutation which produces the amyloidogenic Val30Met TTR protein but no symptoms of FAP.

Diagnosis

Tests that help to diagnose TTR amyloid in the heart

Blood tests: cardiac biomarkers

Amyloid deposits in the heart can cause damage leading to abnormally high concentrations of NT-proBNP (N-terminal fragment of brain natriuretic peptide) and high sensitivity troponin in the blood. These are known as ‘cardiac biomarkers.’

EKG (ECG)

The EKG test is a safe, rapid, routine and painless way of detecting the electrical impulses controlling the heart’s contractions. The impulses are measured and represented on graph paper and can then be interpreted by doctors. EKG appearances test results may raise the suspicion of amyloidosis in the heart.

Echocardiography

Echocardiography is an ultrasound test of the heart. It is safe, routine, and painless with no exposure to radiation. Advanced amyloid deposits in the heart are usually readily detected by an experienced echocardiography operator. At the early stages of amyloid heart disease the findings, cardiac amyloid deposits may be more difficult to detect.

Cardiac magnetic resonance imaging (CMRI)

CMRI is a type of magnetic resonance imaging (MRI) scan. Detailed pictures of the heart are obtained using a magnetic field and radio waves. It is safe and painless, with no exposure to radiation. CMRI can be more helpful than echocardiography in determining whether heart wall thickening is due to amyloidosis or to another cause such as high blood pressure (hypertension). The amyloid deposits within the heart walls, between the heart cells, can be seen clearly in CMR scans. Methods have been developed recently to precisely quantify this so-called interstitial volume and it may therefore become possible in the future to use CMR to obtain accurate measurement of the quantity of amyloid within the heart wall. This would then allow doctors to follow amyloid deposit build-up and to assess regression with treatment.

Radionuclide imaging (DPD scan)

99mTc-DPD, also known as just DPD for short, is a radioactive tracer that homes in specifically on TTR amyloid deposits in the heart. DPD has been used in Europe for bone scans for many years. It has recently been shown to be a valuable method of assessing amyloid deposits in the heart, most useful when the deposits are of TTR type. The amount of DPD taken up by the heart correlates with the amount of TTR amyloid present. Asymptomatic, ‘early stage’ TTR amyloid in the heart can sometimes be detected by DPD scan, when other heart tests appear normal.  Similar types of radionuclide imaging methods are used in other places outside of Europe.  For example, Tc-PYP is often used in the United States.

Tissue biopsy:

Biopsy is the ‘gold standard’ test for diagnosing amyloidosis. This means that it is the best available test, and all other tests should be compared to it. To perform a biopsy, a needle is used to remove a small tissue sample from the body. The sample is then processed in the laboratory using special techniques for identifying amyloid fibrils and examined under a microscope.

Heart biopsy

Heart muscle biopsy is the most definitive way to detect amyloid deposits in the heart. A cardiologist or cardiothoracic surgeon removes a small sample of heart muscle which is then examined under the microscope to detect amyloid deposits. The procedure generally takes less than an hour. The patient is given a sedative medication to put him to sleep. Then the doctor numbs a small area of skin in the neck, and inserts a long, narrow tube called a catheter into a blood vessel. The catheter is threaded through to the heart and its position is checked using X-rays to ensure that the tip is next to the heart wall. Then a tiny heart tissue sample is removed with a grasping device at the end of the catheter. The catheter is then withdrawn, bringing the heart tissue with it. The tissue is sent to the laboratory for analysis.

The procedure is usually safe and painless, and does not require admission to hospital.

Abdominal fat biopsy

Patients with all types of TTR amyloidosis may have amyloid deposits in the fat under the skin, in the stomach area. Sampling of this fat is called an abdominal fat biopsy. The procedure is simple, quick, safe and relatively painless and may be easily performed in an outpatient clinic.

For performance of an abdominal fat biopsy, a doctor numbs a small area of the skin in the abdomen with local anesthetic then inserts a needle into the numb area to take out some fat tissue from underneath the skin.

The fat tissue is then preserved and sent to the laboratory for analysis.

Biopsy tissue processing and examination

The gold standard laboratory test for identification of amyloid in tissue biopsies is staining with the dye called ‘Congo red’, followed by examination of the stained tissue under intense, cross polarized light. When all these techniques are performed correctly, amyloid has a characteristic ‘apple green’ appearance which changes to red as the plane of polarized light is rotated.

If any step in the process is not performed correctly, amyloid may be missed. For this reason, it is important for biopsies to be performed or checked in medical centers experienced in the diagnosis of amyloidosis. False positive and false negative biopsies are quite common when biopsies are performed in insufficiently experienced facilities. Amyloidosis specialist centers may request preserved biopsy slides for review in their own laboratories when seeing patients who were diagnosed elsewhere.

After positive Congo red staining has identified amyloid deposits, further tests are used to identify the type of amyloid present. A technique called immunohistochemistry uses specific antibody molecules that recognize and distinguish between different types of amyloid. If antibodies to TTR stick to the amyloid deposits, this shows that the fibrils are formed from TTR. Another technique that can be useful is called proteomics. This involves use of a laser to cut out amyloid deposits from a section of tissue. The amyloid deposit is then digested with enzymes to break down all the proteins into smaller fragments which can then be precisely identified in a machine called a mass spectrometer. The precise type of TTR amyloidosis can be identified by detection of specific TTR variants in FAP and FAC, and wild type TTR in SSA.

Genetic Testing

Genetic testing involving examination of the DNA from the patient’s blood cells can help doctors to reach an accurate diagnosis. Ordinary blood samples drawn from the patient’s vein are used.

Genetic techniques can identify mutations in the TTR gene. The precise mutation identified may provide information about the likely clinical course. For example, the most common TTR gene mutation worldwide, the Val30Met mutation, often causes FAP with amyloid deposits mostly in the nerves.  In contrast, the Val122lle mutation usually leads to FAC with amyloid deposits mostly in the heart, not in the nerves. If amyloid fibril analysis detects wild type TTR protein and genetic testing does not detect any TTR gene mutations, then the diagnosis is SSA.

Management

The principles of currently available treatment for TTR amyloidosis are listed below.  Unfortunately, no treatments are currently approved for FAC or SSA except supportive care.

1. Reduce the supply of TTR protein
2. Stabilize the TTR tetramer
3. Support the function of organs containing amyloid.

Reducing the TTR supply

At present the only available treatment that reduces the supply of precursor proteins in TTR amyloidosis is liver transplantation for some types of FAP. Liver transplantation is not used to treat TTR cardiac disease, like FAC or SSA. Some new drugs that are currently under evaluation in clinical trials may also reduce TTR amyloid precursor protein supply, such as Ionis’ clinical development program.

Liver transplantation

All of the TTR in the bloodstream is made in the liver. TTR from the liver forms the amyloid deposits everywhere in the body except in the eye and the blood vessels around the brain. Liver transplantation is therefore a treatment option for some patients with FAP. Surgery is performed to remove the patient’s own liver which forms the abnormal, variant TTR. It is replaced by a donor liver making normal, wild type TTR. The aim is to prevent the formation of further amyloid deposits by reducing the supply of the amyloid forming precursor variant TTR.

Since the procedure was introduced in 1991 in a collaboration between Swedish physicians and surgeons and the team from the UK National Amyloidosis Centre, and shown by them to be effective in 1993, hundreds of liver transplantations for FAP have been performed throughout the world. In many patients this has led to stabilization of disease. Most successful outcomes have occurred in patients with the TTR Val30Met mutation, especially if transplantation was performed at a young age and early in the disease course before the heart or nerves sustained too much damage. See The Familial Amyloidotic Polyneuropathy World Transplant Register (FAPWTR) and the Domino Transplant Register: http://www.fapwtr.org/

Unfortunately, amyloid deposits sometimes continue progressing and may even accelerate after transplantation. The existing TTR amyloid deposits apparently act as a template encouraging normal wild type TTR from the donor liver to also form TTR amyloid fibrils and TTR amyloid may therefore continue to accumulate. This problem arises most often in older patients with mutations other than TTR Val30Met.

Liver transplantation is not a treatment for FAC or senile systemic amyloidosis (SSA), because the cardiomyopathy continues to progress due to continued deposition of wild type TTR in the heart.

Stabilizing the TTR tetramer

Tafamidis:

Tafamidis was first developed as a specific drug for FAP. It works by binding and stabilizing TTR in the blood to make it less amyloidogenic. In a trial of tafamidis in 128 patients, early FAP neuropathy progressed at a slower rate in patients who received the drug than in those who did not (Neurology 2012;79:785–792). Tafamidis was approved in Europe to treat Stage 1 FAP in 2012 and in Japan for all stages in 2013.  Tafamidis has not been approved in the U.S. Tafamidis is now being tested in cardiac TTR amyloidosis but has not received approval for this indication.  Information on the safety profile of tafamidis can be found in the product label.

Diflunisal:

Diflunisal is a “non-steroidal anti-inflammatory” (NSAID). This type of drug is often prescribed as a pain killer, for conditions such as arthritis. Diflunisal works by binding and stabilizing TTR in the blood to make it less amyloidogenic. Diflunisal has not been approved for use for TTR amyloidsis by any regulatory body, but a placebo controlled Phase 3 study to look at the efficacy of diflunisal in FAP patients was published in January 2014 (JAMA 2013;310(24):2658-2667). In this study neuropathy progressed at a slower rate in 64 patients with FAP who received diflunisal for 2 years relative to 66 patients who received placebo (dummy pills).  Information on the safety profile of diflunisal can be found in the product label.

Supporting amyloidotic organ function

In TTR amyloidosis, supportive treatment is necessary for heart disease and/ or neuropathy, depending on the symptoms.

TTR amyloid deposits in the heart cause it to stiffen so it cannot pump the blood around the body efficiently, and symptoms of heart failure appear. Standard medications used for heart failure are not helpful for patients with cardiac amyloidosis but simple measures with a focus on careful fluid balance can be helpful.

Fluid balance – the 3Ds

Fluid build- up due to heart stiffness causes leg swelling (edema) and breathlessness due to fluid in the lungs. This problem may be exacerbated if the patient drinks too much fluid. So doctors may recommend that patients with TTR cardiac amyloidosis should limit their fluid intake.

Medical recommendations may include paying attention to the 3 Ds:

1. Diet: steady intake of up to 1.5 liters per day and limitation of salt consumption may be recommended.
2. Diuretics: doctors may prescribe water tablets, known as diuretics, such as furosemide or spironolactone. These increase urine production, so excess salt and water are removed from the body, improving ankle edema and breathlessness.
3. Daily weights: doctors may recommend that patients weigh themselves daily on the same scales, at the same time of day, ideally in the morning, wearing just underclothes, and report weight fluctuations to the doctor. Small weight increases may be an early sign of fluid excess.

Support stockings may be recommended for patients with leg edema (swelling).

If there is light-headedness, fatigue on minor exertion or fainting due to blood pressure drops, doctors may advise careful position changing from lying to sitting, sitting to standing and standing to walking.

Special medication considerations

Doctors may recommend that the following drug classes should be used with caution by patients with TTR amyloid in the heart:

• calcium channel blockers
• digoxin
• angiotensin converting enzyme (ACE) inhibitors
• angiotensin receptor blockers
• beta blockers

In some cases anticoagulation (warfarin) may be recommended.
A pacemaker or an implantable cardioverter-defibrillator (ICD) may be recommended if there is a slow or irregular heart rate, or episodes of very fast heart rate, tachycardia.

Heart transplantation

Combined heart and liver transplant has been performed in a few dozen patients with FAP worldwide. This is major surgery with significant associated risks, so it is only a possible option for a small minority of patients, usually those who are diagnosed at a relatively young age.
Heart transplantation is a major operation with a high risk of complications, especially in elderly people, so it is not usually a viable option for patients with FAC and SSA. Very rarely these conditions may be diagnosed at a younger age than 60, and heart transplantation may occasionally be considered if such patients are otherwise healthy.

New drugs for TTR amyloidosis

A number of new drugs for TTR amyloidosis are in various stages of development, around the world, offering hope for the near future to patients with TTR amyloidosis. These include IONIS-TTR_Rx (described below), patisiran, ALN-TTR_sc, CPHPC+anti-SAP antibodies, doxycycline and TUCA.

A new drug in clinical development – IONIS-TTR_Rx

IONIS-TTR_Rx is a new, first in class drug developed by Ionis Pharmaceuticals with the aim of reducing the supply of TTR precursor proteins in patients with TTR amyloidosis. IONIS-TTR_Rx is currently in clinical trials in patients with FAP. Studies to evaluate IONIS-TTR_Rx in patients with FAC or SSA may initiate in the near future.  It is not yet licensed and is only available at present to patients with FAP who are participating in these trials.

IONIS-TTR_Rx directly targets and reduces TTR production at the level of the genetic machinery inside the liver cells. When TTR production is shut down in this manner, the supply of TTR protein is reduced, which should reduce or prevent the formation of new TTR amyloid deposits in the tissues. Existing deposits may then become smaller, as the body clears them away, and organ function may stop deteriorating. Because IONIS-TTR_Rx reduces production of both variant and wild type TTR, this drug has the potential to be beneficial for patients with all three types of TTR amyloidosis (FAP, FAC, and SSA). A short-term clinical trial in healthy volunteers demonstrated that IONIS-TTR_Rx was well-tolerated and dramatically reduced TTR concentrations in the blood. Evidence regarding efficacy in controlling TTR amyloidosis is not yet available.