**2.2 AL amyloidosis**

*Amyloid Diseases*

*2.1.2 Treatment*

shown to reverse organ function.

resulting in organ dysfunction. These include mutations in the genes encoding transthyretin, the fibrinogen A α-chain, apolipoprotein A-I, apolipoprotein A-II, and lysozyme [10]. These mutations appear to account for the vast majority of relatively rare familial amyloidosis. Each of these has clinical characteristics that are

Amyloidosis may be localized, or systemic. The clinical symptoms of AA amyloidosis depend on the organ involved by the amyloid fibril. Liver and spleen are the most common sites of deposition, but they are asymptomatic until late in the course of the disease. Hepatosplenomegaly and adrenal insufficiency are common in the advanced stage of AA amyloidosis. Renal involvement damages the glomerular membrane, resulting in nephrotic syndrome and proteinuria. Proteinuria is one of the earliest signs of AA amyloidosis, and seen in approximately 95% of patients with AA amyloidosis [2, 11]. Persistent, untreated renal damage results in end stage renal disease (ESRD), requiring some form of renal substitute therapy—either dialysis or renal transplantation. Cardiac involvement is by deposition of fibrils into cardiac muscle, but clinical cardiac dysfunction is extremely rare in AA amyloidosis, occurring in only 2% of patients in most series [12]. Gastrointestinal involvement results in diarrhea, malabsorption and pseudo obstruction of the bowel. There

are several reports of thyroid gland involvement, manifesting as goiter [13].

Treatment of AA amyloidosis is challenging due to diverse underlying causes. Ideally, in inflammatory disorders—whether chronic infectious disease (e.g., mycobacterium tuberculosis, staphylococcal osteomyelitis, and other chronic infections), autoimmune disease (e.g., rheumatoid arthritis, scleroderma, and other immune mediated inflammatory diseases), idiopathic (e.g., sarcoidosis), and chronic low-grade malignancy (e.g., B and T cell low-grade lymphomas, Hodgkin disease) the treatment of AA amyloidosis is the treatment of the underlying disease process. The role of controlling inflammation is also essential in the management of AA amyloidosis in patients with chronic rheumatologic diseases. In the era of advanced therapies, the incidence of rheumatic arthritis leading to AA amyloidosis has declined significantly; this was at one time among the most common causes. Specific treatments such as surgical excision in Castleman disease, high dose colchicine for familial Mediterranean fever (FMF) and effective therapy for tuberculosis have shown to significantly reduce serum SAA levels thereby improvement in end organ dysfunction. Treatments of malignancy with chemotherapy and surgery have

Several anti-inflammatory agents have been studied as potential therapy to reduce the levels of SAA. Tocilizumab, a monoclonal antibody against IL-6 has been successful in significantly reducing circulating levels of SAA when used in autoimmune diseases. A recent series showed significant reduction in acute phase reactants as well as an improvement in proteinuria in patients treated with Tocilizumab for

In vitro studies have shown low molecular weight heparin to impair amyloid deposition by impeding the structural changes necessary for fibril formation. Eporsidate, a sulfonated small molecule similar to heparin sulfate binds competitively to glycosaminoglycan and reduces inflammation and amyloid deposition. This was initially studied as an agent to retard progressive renal failure, and it resulted in a favorable response in a phase II clinical trial [15]. Unfortunately, a

somewhat peculiar to the specific etiology of the inherited disorder.

*2.1.1 Clinical features of systemic AA amyloidosis*

**6**

FMF [14].

AL amyloidosis results from the deposition of abnormally folded immunoglobulin light chains into tissues. The formation of amyloid fibrils from immunoglobulin light chains requires abnormal three-dimensional folding of the light chain, resulting in filaments of β-sheets of relatively insoluble protein [20]. AL amyloid may arise from either polyclonal immunoglobulin light chains or, much more commonly, from monoclonal immunoglobulin light chains. In order for polyclonal AL amyloidosis to result, however, the light chains must fold abnormally—in order to form amyloid and accumulate in target organs. Further, the local concentration of these peptides must, in general, be high. In AL amyloidosis, whether polyclonal or monoclonal, the specific light chains have a peptide sequence that results in a predisposition to abnormal folding of the peptide. In some cases, this appears to be due to genetic polymorphisms in the light chain gene structure. Among the variable regions of the light chain gene products, several (Vλ1, Vλ2, Vλ3, Vλ6, and Vκ1) are over-represented as amyloid protein, suggesting that these peptide sequences have a predilection to fold abnormally and become amyloid. In monoclonal AL amyloidosis, the tendency of monoclonal light chain to fold abnormally may be due, rather, to a mutational event attributable to genomic instability of the clone, rather than a genetic polymorphism in the light chain sequence. Several laboratories have demonstrated that peptide sequences from patients with different levels of secreted light chain have distinct differences in the location of non-conservative mutations in the light chain genes. This implies that the location of non-conservative mutations may be one determinant of the amyloidogenic propensity of light chains in some cases. Three-dimensional structure analyses and site-mutagenesis experiments indicate that both replacement of conserved polar residues in light chains, and loss of hydrogen bonding sites, are common features seen in amyloidogenic immunoglobulin light chains [21–24]. Separately, there is evidence that posttranslational modification of light chains can influence the propensity for amyloid to accumulate, including peptide glycosylation, lysine modification, and rate of proteolysis. Impaired function of metalloproteases that degrade extracellular matrix proteins have been implicated in the propensity of amyloid to accumulate. There is also strong evidence that glycosaminoglycans of the extracellular matrix—particularly heparan sulfate, but also dermatan sulfate and chondroitin sulfate, interact with amyloid protein, providing a scaffold for the polymerized amyloid fibrils [25]. The relative concentration of these glycosaminoglycans appears to impact on the propensity of amyloid to be deposited. It should be noted that in a recent series from China, Huang and Liu reported that immunoglobulin heavy chain amyloidosis accounted for 3.7% of cases of amyloidosis, as compared to AL amyloidosis accounting for 93% of cases. In that report, AA amyloidosis accounted for only 2.2% of all patients with systemic amyloidosis [26].

### *2.2.1 Polyclonal AL amyloidosis*

The Mayo Clinic pioneered the use of Mass Spectroscopy and High Performance Chromatography to identify the specific proteins present in amyloid tissue specimens. They have applied that technology to determine, from patient samples, whether a patient's amyloid is AA or AL, and to further characterize if an AL specimen is entirely kappa or lambda light chains—consistent with a monoclonal process; or if the AL amyloid is an approximately equal mix of both kappa and lambda light chains—suggesting a polyclonal process. In a 2013 report, Grogg and colleagues identified two patients with pulmonary amyloidosis in whom Liquid Chromatography-Mass Spectroscopy documented equal amounts of kappa and of lambda light chain in the amyloid deposits. In addition, the polyclonal identity of the amyloid was demonstrated by immunohistochemical staining for kappa and lambda light chains, and polymerase chain reaction amplification of immunoglobulin gene sequence showed only a polyclonal population in these patients [27]. In 2016, the Mayo Clinic studied in detail a patient with localized amyloidosis of the oropharynx. Liquid Chromatography and Mass Spectroscopy documented polyclonal AL amyloid, with equal proportions of kappa and lambda light chains present. No monoclonal protein was identified, and no monoclonal lymphoid or plasma cell population was present. Thus, this group has well documented the process of localized amyloidosis attributable to polyclonal light chain deposition. In that report they also summarized data regarding an additional 17 patients identified from the medical literature with isolated amyloidosis of the palate [28]. In three of those seventeen cases, a plasma cell dyscrasia was present (MGUS in two and myeloma in one). Similarly, Wey and colleagues from Taiwan reported a patient with Sjogren's syndrome complicated by localized, cutaneous nodular amyloidosis of the legs. In this case, C-reactive protein 0.12 mg/dL antinuclear antibody titer, anti-centromere antibody titer, and anti-Ro/SSA antibody titer were all pathologically elevated and polyclonal gammaglobulinemia was detected by serum immune-electrophoresis [29]. Thus, multiple investigators have substantiated the observation that AL amyloid can be polyclonal. Definitive data regarding the relative incidence of monoclonal versus polyclonal AL amyloid is not available. However, it does appear from these cases that polyclonal AL amyloidosis seems to be a more indolent process and less aggressive than AL amyloidosis, and is most often a localized process. In these cases, local therapy appears likely to control the disease. Nonetheless, there are documented cases of systemic polyclonal AL amyloidosis with multi-organ involvement and relatively poor prognosis as compared to age-matched individuals without amyloidosis.

Localized amyloidosis is much rarer than systemic amyloidosis, predominantly affects the skin or mucosal tissues (86%), and is usually of the AL subtype (98%). It is generally accepted that localized AL amyloidosis results from monoclonal light chains. However, the most recent amyloid nomenclature developed by the International Society of Amyloidosis in 2014 does not distinguish between monoclonal and polyclonal sources.

#### *2.2.2 Monoclonal AL amyloidosis*

In contrast to polyclonal AL amyloidosis, monoclonal AL amyloidosis is typically an aggressive, multi-organ disease with a generally poor prognosis. The disease process is driven by production of a monoclonal immunoglobulin light chain hence the name AL (amyloid, light chain). As noted previously, only a minority of monoclonal light chain gammopathy results in amyloidosis. The exonic coding sequence for the specific light chain will most often have either a mutation, or a

**9**

*The Clinical Spectrum of Amyloidosis*

*DOI: http://dx.doi.org/10.5772/intechopen.82763*

larly periorbital purpura, as a notable finding.

*2.2.3 Clinical features of AL amyloidosis*

polymorphism, that results in abnormal protein folding, in order for the light chain to be deposited as amyloid and cause organ dysfunction, as previously discussed. AL amyloid is found both extracellularly and intracellularly, in affected organs. Kyle and colleagues at the Mayo Clinic reported that the incidence of AL amyloid in Olmsted County, Minnesota, was in the range of 3–5 cases per million annually [30]. Others have estimated the annual incidence to be in the range of 10–14 patients per million. In contrast, it is estimated that the annual incidence of MGUS in men is 120 per 100,000 population at the age of 50 years, and increases to 530 per 100,000 population at the age of 90 years. The incidence of multiple myeloma is in the range of 85 cases per million annually in the United States. Thus, only a very small minority of patients with MGUS or overt multiple myeloma develop clinical AL amyloidosis. The average age at diagnosis of patients with AL amyloidosis is approximately

64. The disease appears to occur more commonly in males than females [31]. Presenting signs and symptoms of amyloidosis are the consequences of specific organ involvement. Cardiac involvement occurs in the majority of patients diagnosed as having AL amyloidosis, most typically presenting with symptoms and signs of heart failure syndrome but with a preserved left ventricular ejection fraction. In an excellent recent review, Gertz reported that 71% of patients with AL amyloidosis seen at the Mayo Clinic had cardiac involvement, with 58% having kidney disease [32]. Renal involvement most often includes nephrotic range proteinuria; in an early series reported by Kyle in 1975, of all patients reviewed in that series with any type of amyloidosis, approximately 90% had some degree of proteinuria. Neurologic involvement occurs in approximately 25% of patients, and may include peripheral neuropathies, including, most commonly carpet tunnel syndrome; or autonomic neuropathy—most prominently orthostatic hypotension but also including anhydrosis [33]. Organ enlargement is common, with as many as half of patients having hepatomegaly, and an enlarged tongue (macroglossia) occurs in approximately a quarter of patients. Kyle also described purpura, particu-

AL amyloid is most commonly a systemic disorder. However, there are cases of AL amyloidosis localized to a single site. The sites of localized AL amyloid reported include the skin, the larynx, the gastrointestinal tract, and the urinary bladder. Diagnosis must be confirmed by tissue biopsy, in order to demonstrate the presence of the amyloid by Congo red histologic staining. When a clinician encounters a patient over the age of 60 with suspected systemic AL amyloidosis, serum protein electrophoresis is essential to determine if a monoclonal serum para-protein is present. If a monoclonal protein is either suspected or identified, then serum protein immune-electro fixation or immunoelectrophoresis is indicated. Once a monoclonal serum paraprotein is identified, bone marrow biopsy and aspirate should be obtained in order to assess the percentage of clonal plasma cells infiltrating of the marrow, and determine if the patient meets the criteria for diagnosis of multiple myeloma or a lymphoplasmacytic lymphoma. In patients with a clonal AL amyloid, treatment to eradicate the clone of plasma cells or lymphocytes producing the light chain, if successful, will prevent synthesis of new immunoglobulin light chains, and, if the patient can be supported to survive long enough, organ recovery may occur over time as the relatively insoluble amyloid is ultimately metabolized and broken down.

The clinical features of AL amyloidosis are extremely variable from one patient to the next; nearly every organ can potentially be involved. However, the disease has a stereotypic pattern of presentation in many cases. As noted earlier, systemic AL amyloidosis involves the heart in approximately 70–80% of cases, depending

#### *The Clinical Spectrum of Amyloidosis DOI: http://dx.doi.org/10.5772/intechopen.82763*

*Amyloid Diseases*

*2.2.1 Polyclonal AL amyloidosis*

The Mayo Clinic pioneered the use of Mass Spectroscopy and High Performance Chromatography to identify the specific proteins present in amyloid tissue specimens. They have applied that technology to determine, from patient samples, whether a patient's amyloid is AA or AL, and to further characterize if an AL specimen is entirely kappa or lambda light chains—consistent with a monoclonal process; or if the AL amyloid is an approximately equal mix of both kappa and lambda light chains—suggesting a polyclonal process. In a 2013 report, Grogg and colleagues identified two patients with pulmonary amyloidosis in whom Liquid Chromatography-Mass Spectroscopy documented equal amounts of kappa and of lambda light chain in the amyloid deposits. In addition, the polyclonal identity of the amyloid was demonstrated by immunohistochemical staining for kappa and lambda light chains, and polymerase chain reaction amplification of immunoglobulin gene sequence showed only a polyclonal population in these patients [27]. In 2016, the Mayo Clinic studied in detail a patient with localized amyloidosis of the oropharynx. Liquid Chromatography and Mass Spectroscopy documented polyclonal AL amyloid, with equal proportions of kappa and lambda light chains present. No monoclonal protein was identified, and no monoclonal lymphoid or plasma cell population was present. Thus, this group has well documented the process of localized amyloidosis attributable to polyclonal light chain deposition. In that report they also summarized data regarding an additional 17 patients identified from the medical literature with isolated amyloidosis of the palate [28]. In three of those seventeen cases, a plasma cell dyscrasia was present (MGUS in two and myeloma in one). Similarly, Wey and colleagues from Taiwan reported a patient with Sjogren's syndrome complicated by localized, cutaneous nodular amyloidosis of the legs. In this case, C-reactive protein 0.12 mg/dL antinuclear antibody titer, anti-centromere antibody titer, and anti-Ro/SSA antibody titer were all pathologically elevated and polyclonal gammaglobulinemia was detected by serum immune-electrophoresis [29]. Thus, multiple investigators have substantiated the observation that AL amyloid can be polyclonal. Definitive data regarding the relative incidence of monoclonal versus polyclonal AL amyloid is not available. However, it does appear from these cases that polyclonal AL amyloidosis seems to be a more indolent process and less aggressive than AL amyloidosis, and is most often a localized process. In these cases, local therapy appears likely to control the disease. Nonetheless, there are documented cases of systemic polyclonal AL amyloidosis with multi-organ involvement and relatively poor prognosis as compared to age-matched individuals

Localized amyloidosis is much rarer than systemic amyloidosis, predominantly affects the skin or mucosal tissues (86%), and is usually of the AL subtype (98%). It is generally accepted that localized AL amyloidosis results from monoclonal light chains. However, the most recent amyloid nomenclature developed by the International Society of Amyloidosis in 2014 does not distinguish between mono-

In contrast to polyclonal AL amyloidosis, monoclonal AL amyloidosis is typically

an aggressive, multi-organ disease with a generally poor prognosis. The disease process is driven by production of a monoclonal immunoglobulin light chain hence the name AL (amyloid, light chain). As noted previously, only a minority of monoclonal light chain gammopathy results in amyloidosis. The exonic coding sequence for the specific light chain will most often have either a mutation, or a

**8**

without amyloidosis.

clonal and polyclonal sources.

*2.2.2 Monoclonal AL amyloidosis*

polymorphism, that results in abnormal protein folding, in order for the light chain to be deposited as amyloid and cause organ dysfunction, as previously discussed. AL amyloid is found both extracellularly and intracellularly, in affected organs. Kyle and colleagues at the Mayo Clinic reported that the incidence of AL amyloid in Olmsted County, Minnesota, was in the range of 3–5 cases per million annually [30]. Others have estimated the annual incidence to be in the range of 10–14 patients per million. In contrast, it is estimated that the annual incidence of MGUS in men is 120 per 100,000 population at the age of 50 years, and increases to 530 per 100,000 population at the age of 90 years. The incidence of multiple myeloma is in the range of 85 cases per million annually in the United States. Thus, only a very small minority of patients with MGUS or overt multiple myeloma develop clinical AL amyloidosis. The average age at diagnosis of patients with AL amyloidosis is approximately 64. The disease appears to occur more commonly in males than females [31].

Presenting signs and symptoms of amyloidosis are the consequences of specific organ involvement. Cardiac involvement occurs in the majority of patients diagnosed as having AL amyloidosis, most typically presenting with symptoms and signs of heart failure syndrome but with a preserved left ventricular ejection fraction. In an excellent recent review, Gertz reported that 71% of patients with AL amyloidosis seen at the Mayo Clinic had cardiac involvement, with 58% having kidney disease [32]. Renal involvement most often includes nephrotic range proteinuria; in an early series reported by Kyle in 1975, of all patients reviewed in that series with any type of amyloidosis, approximately 90% had some degree of proteinuria. Neurologic involvement occurs in approximately 25% of patients, and may include peripheral neuropathies, including, most commonly carpet tunnel syndrome; or autonomic neuropathy—most prominently orthostatic hypotension but also including anhydrosis [33]. Organ enlargement is common, with as many as half of patients having hepatomegaly, and an enlarged tongue (macroglossia) occurs in approximately a quarter of patients. Kyle also described purpura, particularly periorbital purpura, as a notable finding.

AL amyloid is most commonly a systemic disorder. However, there are cases of AL amyloidosis localized to a single site. The sites of localized AL amyloid reported include the skin, the larynx, the gastrointestinal tract, and the urinary bladder. Diagnosis must be confirmed by tissue biopsy, in order to demonstrate the presence of the amyloid by Congo red histologic staining. When a clinician encounters a patient over the age of 60 with suspected systemic AL amyloidosis, serum protein electrophoresis is essential to determine if a monoclonal serum para-protein is present. If a monoclonal protein is either suspected or identified, then serum protein immune-electro fixation or immunoelectrophoresis is indicated. Once a monoclonal serum paraprotein is identified, bone marrow biopsy and aspirate should be obtained in order to assess the percentage of clonal plasma cells infiltrating of the marrow, and determine if the patient meets the criteria for diagnosis of multiple myeloma or a lymphoplasmacytic lymphoma. In patients with a clonal AL amyloid, treatment to eradicate the clone of plasma cells or lymphocytes producing the light chain, if successful, will prevent synthesis of new immunoglobulin light chains, and, if the patient can be supported to survive long enough, organ recovery may occur over time as the relatively insoluble amyloid is ultimately metabolized and broken down.

### *2.2.3 Clinical features of AL amyloidosis*

The clinical features of AL amyloidosis are extremely variable from one patient to the next; nearly every organ can potentially be involved. However, the disease has a stereotypic pattern of presentation in many cases. As noted earlier, systemic AL amyloidosis involves the heart in approximately 70–80% of cases, depending

on the series. The most common clinical presentation of symptomatic organic heart disease due to AL amyloidosis is heart failure syndrome, with dyspnea and often leg swelling (edema), although angina pectoris (chest pain due to ischemia) may also occur, as well as arrhythmias. Prior to onset of clinically evident heart disease, nearly all patients with cardiac involvement by amyloidosis will have an elevated serum level of N-terminal Pro-natriuretic peptide Type B (NT-ProBNP). Progressive elevation of the Pro-BNP correlates with progressively poorer prognosis, and the level of Pro-BNP is a criterion for risk stratification and prognosis in several staging systems for cardiac amyloidosis. Similarly, cardiac troponin T (cTnT) and cardiac troponin I (cTnI) are sensitive (although not specific) markers of myocardial damage. The degree of elevation of these proteins are additional markers of myocardial cell damage in cardiac amyloidosis [34]. A characteristic finding on electrocardiogram is decreased voltage in the limb leads, as compared to normal; however, this is not a consistent finding even in patients with biopsy proven cardiac amyloidosis. Imaging of the heart by echocardiogram may demonstrate the characteristic amyloidosis findings of pathologically increased ventricular wall thickness, as well as a granular, sparkling appearance of the myocardium on three-dimensional echocardiographic imaging. Again, there is the caveat that early in the disease process these findings may not be evident. A longitudinal "strain" pattern may also be present, but again is not a specific finding for amyloidosis [35]. Technetium-99 pyrophosphate scanning of the heart, particularly with single photon emission computed tomography (SPECT), is a sensitive imaging technique that will show retention of the radionuclide in cases of cardiac amyloidosis; this is widely considered a diagnostic study of choice. Technetium-99 pyrophosphate scanning of the heart can often distinguish between ATTR amyloid and AL amyloid. Magnetic Resonance Imaging of the heart using the contrast agent gadolinium for enhancement, a more costly approach than echocardiogram or Technetium-99 scan, can provide evidence of cardiac amyloidosis. Delayed enhancement pulse sequences following infusion of the gadolinium will most often demonstrate a diffuse and irregular hyper-enhancement of the myocardium in patients with cardiac amyloidosis. Subendocardial late gadolinium enhancement (LGE) occurs more commonly in AL amyloidosis, and transmural LGE more commonly in ATTR cardiac amyloidosis. In this context, even greater specificity may be achieved using a Magnetic Resonance Imaging technique termed "myocardial nulling." This technique exploits the observation that gadolinium contrast accumulates excessively and abnormally in myocardial tissue, that has accumulated amyloid, and the findings are quite specific for amyloidosis of the heart.

Several groups have developed staging systems that stratify cardiac prognosis in patients with AL amyloidosis. The Mayo Clinic group Cardiac Staging System stratifies patients based on the combination of NT-proBNP together with either the cTnT or the cTnI. These parameters may be used to assess prognosis at the time of initial diagnosis, and often form a part of eligibility criteria for clinical trials [36].

As noted, clinically evident heart disease in AL amyloidosis manifests most often as congestive heart failure syndrome, despite preservation of the left ventricular ejection fraction. The symptoms most often include fatigue and exertional dyspnea, as well as edema due to heart failure, in some cases. Signs may include a lateral shift of the cardiac point of maximal impulse, as well as adventitial heart sounds and murmurs. Cardiomegaly may be evident on chest radiogram. Due to amyloid deposition, a fraction of patients will have electrical conduction abnormalities, and resultant cardiac arrhythmias. Such arrhythmias may result in sudden cardiac death, if the abnormal rhythm does not result in non-lethal signs or symptoms first.

Second to cardiac manifestations, the most common organ clinically involved by systemic AL amyloidosis are the kidneys. Kidney disease due to amyloid seen in

**11**

cytopenias.

*The Clinical Spectrum of Amyloidosis*

have AL amyloidosis.

weight loss on this basis.

cally mimic other muscle wasting diseases [38].

*DOI: http://dx.doi.org/10.5772/intechopen.82763*

approximately 50–60% of patients, depending on the series. The organ tropism of AL amyloid correlates with the variable region gene sequence, and the IGLV6-57 gene sequence appears to predispose to renal involvement. Within the affected kidney, amyloid deposits are seen prominently in the glomeruli, with additional amyloid seen in blood vessels, in tubular-basement membranes, and in the interstitial space. Uptake of amyloid by mesangial cells induces a functional change in phenotype resulting in cellular dysfunction. In experimental models, uptake of amyloid results in a transformation of a mesangial cell from a smooth muscle cells to a macrophage phenotype. Renal dysfunction clinically is typically manifest first as a protein wasting process, which typically progresses to nephrotic range proteinuria. Nephrotic range proteinuria results in edema and with time leads to chronic kidney disease with progressive edema, followed by electrolyte disorders and progressively worsening glomerular filtration rate [37]. Because of urinary loss of natural anticoagulants such as Protein C, which has a relatively short half-life, venous thrombosis may occur in patients with Amyloidosis and renal disease. Both renal involvement by AL amyloidosis, and cardiac disease due to AL amyloidosis, contribute to the generalized weakness experienced by a majority of patients who

The nervous system is clinically involved in AL amyloidosis in approximately 20% of patients. The most common neurologic process seen is a sensory peripheral neuropathy, which is often painful. Dysautonomia is also seen, particularly manifesting as orthostatic hypotension due to amyloid damaging the autonomic regulation of blood pressure. Orthostatic hypotension can be disabling, and may result in falls and therefore fractures. Patients with severe orthostatic hypotension may remain bedridden to avoid symptoms, and are then at risk both for developing decubitus ulcers, as well as venous thromboses. Myopathy may also occur because of AL amyloid deposition, and may present as pseudo-hypertrophy, or may clini-

The gastrointestinal tract is involved by AL amyloidosis. In a recent report from Stanford University Medical Center, Yen and colleagues reported that in a retrospective analysis of 583 patients with amyloidosis, approximately 16% had gastrointestinal symptoms. They observed that 50% of patients with amyloid had nausea, vomiting, or abdominal pain. In this cohort, approximately 82% of patients had AL amyloid. A classic finding reported in the earliest descriptions of amyloidosis is macroglossia, an enlarged tongue. However, it is estimated that this is seen in only about 15% of patients [39]. Malabsorption is often seen in amyloidosis of the gastrointestinal tract, with consequence diarrhea, abdominal discomfort, and

Patients with kappa light chain AL amyloidosis have been reported to have a greater propensity for hepatic involvement than lambda light chain amyloidosis [40]. In contrast, dominant soft-tissue and bone involvement is associated with the IGLV3-1 gene, and in some reports, the Kappa 1 light chain. Hepatic involvement is typically manifest as hepatomegaly, and biopsy typically documents the presence of amyloid [41]. Splenomegaly is also common, particularly when hepatomegaly is present, and splenomegaly may result in blood cell sequestration in the spleen, with

Amyloid infiltration has been reported in virtually every gland, although these reports suggest that direct endocrine dysfunction due to amyloidosis is relatively less common than involvement by the heart, kidneys, and neurologic systems [42]. Amyloidosis of the breast have been reported, as well as amyloidosis of the seminal vesicles also occurs. Amyloidosis can infiltrate the pancreas, and amyloid infiltration of the adrenal gland may result in adrenal insufficiency. Similarly, amyloid infiltration of the pituitary gland can result in polyendocrine dysfunction.

#### *The Clinical Spectrum of Amyloidosis DOI: http://dx.doi.org/10.5772/intechopen.82763*

*Amyloid Diseases*

on the series. The most common clinical presentation of symptomatic organic heart disease due to AL amyloidosis is heart failure syndrome, with dyspnea and often leg swelling (edema), although angina pectoris (chest pain due to ischemia) may also occur, as well as arrhythmias. Prior to onset of clinically evident heart disease, nearly all patients with cardiac involvement by amyloidosis will have an elevated serum level of N-terminal Pro-natriuretic peptide Type B (NT-ProBNP). Progressive elevation of the Pro-BNP correlates with progressively poorer prognosis, and the level of Pro-BNP is a criterion for risk stratification and prognosis in several staging systems for cardiac amyloidosis. Similarly, cardiac troponin T (cTnT) and cardiac troponin I (cTnI) are sensitive (although not specific) markers of myocardial damage. The degree of elevation of these proteins are additional markers of myocardial cell damage in cardiac amyloidosis [34]. A characteristic finding on electrocardiogram is decreased voltage in the limb leads, as compared to normal; however, this is not a consistent finding even in patients with biopsy proven cardiac amyloidosis. Imaging of the heart by echocardiogram may demonstrate the characteristic amyloidosis findings of pathologically increased ventricular wall thickness, as well as a granular, sparkling appearance of the myocardium on three-dimensional echocardiographic imaging. Again, there is the caveat that early in the disease process these findings may not be evident. A longitudinal "strain" pattern may also be present, but again is not a specific finding for amyloidosis [35]. Technetium-99 pyrophosphate scanning of the heart, particularly with single photon emission computed tomography (SPECT), is a sensitive imaging technique that will show retention of the radionuclide in cases of cardiac amyloidosis; this is widely considered a diagnostic study of choice. Technetium-99 pyrophosphate scanning of the heart can often distinguish between ATTR amyloid and AL amyloid. Magnetic Resonance Imaging of the heart using the contrast agent gadolinium for enhancement, a more costly approach than echocardiogram or Technetium-99 scan, can provide evidence of cardiac amyloidosis. Delayed enhancement pulse sequences following infusion of the gadolinium will most often demonstrate a diffuse and irregular hyper-enhancement of the myocardium in patients with cardiac amyloidosis. Subendocardial late gadolinium enhancement (LGE) occurs more commonly in AL amyloidosis, and transmural LGE more commonly in ATTR cardiac amyloidosis. In this context, even greater specificity may be achieved using a Magnetic Resonance Imaging technique termed "myocardial nulling." This technique exploits the observation that gadolinium contrast accumulates excessively and abnormally in myocardial tissue, that has accumulated amyloid, and the

findings are quite specific for amyloidosis of the heart.

Several groups have developed staging systems that stratify cardiac prognosis in patients with AL amyloidosis. The Mayo Clinic group Cardiac Staging System stratifies patients based on the combination of NT-proBNP together with either the cTnT or the cTnI. These parameters may be used to assess prognosis at the time of initial

As noted, clinically evident heart disease in AL amyloidosis manifests most often as congestive heart failure syndrome, despite preservation of the left ventricular ejection fraction. The symptoms most often include fatigue and exertional dyspnea, as well as edema due to heart failure, in some cases. Signs may include a lateral shift of the cardiac point of maximal impulse, as well as adventitial heart sounds and murmurs. Cardiomegaly may be evident on chest radiogram. Due to amyloid deposition, a fraction of patients will have electrical conduction abnormalities, and resultant cardiac arrhythmias. Such arrhythmias may result in sudden cardiac death, if the abnormal rhythm does not result in non-lethal signs or symptoms first. Second to cardiac manifestations, the most common organ clinically involved by systemic AL amyloidosis are the kidneys. Kidney disease due to amyloid seen in

diagnosis, and often form a part of eligibility criteria for clinical trials [36].

**10**

approximately 50–60% of patients, depending on the series. The organ tropism of AL amyloid correlates with the variable region gene sequence, and the IGLV6-57 gene sequence appears to predispose to renal involvement. Within the affected kidney, amyloid deposits are seen prominently in the glomeruli, with additional amyloid seen in blood vessels, in tubular-basement membranes, and in the interstitial space. Uptake of amyloid by mesangial cells induces a functional change in phenotype resulting in cellular dysfunction. In experimental models, uptake of amyloid results in a transformation of a mesangial cell from a smooth muscle cells to a macrophage phenotype. Renal dysfunction clinically is typically manifest first as a protein wasting process, which typically progresses to nephrotic range proteinuria. Nephrotic range proteinuria results in edema and with time leads to chronic kidney disease with progressive edema, followed by electrolyte disorders and progressively worsening glomerular filtration rate [37]. Because of urinary loss of natural anticoagulants such as Protein C, which has a relatively short half-life, venous thrombosis may occur in patients with Amyloidosis and renal disease. Both renal involvement by AL amyloidosis, and cardiac disease due to AL amyloidosis, contribute to the generalized weakness experienced by a majority of patients who have AL amyloidosis.

The nervous system is clinically involved in AL amyloidosis in approximately 20% of patients. The most common neurologic process seen is a sensory peripheral neuropathy, which is often painful. Dysautonomia is also seen, particularly manifesting as orthostatic hypotension due to amyloid damaging the autonomic regulation of blood pressure. Orthostatic hypotension can be disabling, and may result in falls and therefore fractures. Patients with severe orthostatic hypotension may remain bedridden to avoid symptoms, and are then at risk both for developing decubitus ulcers, as well as venous thromboses. Myopathy may also occur because of AL amyloid deposition, and may present as pseudo-hypertrophy, or may clinically mimic other muscle wasting diseases [38].

The gastrointestinal tract is involved by AL amyloidosis. In a recent report from Stanford University Medical Center, Yen and colleagues reported that in a retrospective analysis of 583 patients with amyloidosis, approximately 16% had gastrointestinal symptoms. They observed that 50% of patients with amyloid had nausea, vomiting, or abdominal pain. In this cohort, approximately 82% of patients had AL amyloid. A classic finding reported in the earliest descriptions of amyloidosis is macroglossia, an enlarged tongue. However, it is estimated that this is seen in only about 15% of patients [39]. Malabsorption is often seen in amyloidosis of the gastrointestinal tract, with consequence diarrhea, abdominal discomfort, and weight loss on this basis.

Patients with kappa light chain AL amyloidosis have been reported to have a greater propensity for hepatic involvement than lambda light chain amyloidosis [40]. In contrast, dominant soft-tissue and bone involvement is associated with the IGLV3-1 gene, and in some reports, the Kappa 1 light chain. Hepatic involvement is typically manifest as hepatomegaly, and biopsy typically documents the presence of amyloid [41]. Splenomegaly is also common, particularly when hepatomegaly is present, and splenomegaly may result in blood cell sequestration in the spleen, with cytopenias.

Amyloid infiltration has been reported in virtually every gland, although these reports suggest that direct endocrine dysfunction due to amyloidosis is relatively less common than involvement by the heart, kidneys, and neurologic systems [42]. Amyloidosis of the breast have been reported, as well as amyloidosis of the seminal vesicles also occurs. Amyloidosis can infiltrate the pancreas, and amyloid infiltration of the adrenal gland may result in adrenal insufficiency. Similarly, amyloid infiltration of the pituitary gland can result in polyendocrine dysfunction.

#### *Amyloid Diseases*

Cutaneous AL amyloidosis is well described, and most often presents as either hemorrhagic bullous lesions, or, classically, as purpura or ecchymosis. Among the early classic descriptions of cutaneous manifestations of amyloidosis is the phenomenon of periorbital purpura [43].

Patients with AL amyloidosis may have one or more acquired coagulopathies, resulting in a bleeding diathesis. This may be due to impaired synthesis of clotting proteins by a liver involved by amyloid infiltration; however, adsorption of coagulation proteins, most commonly Factor X, but other factors as well, results in increased clearance of coagulation proteins and a bleeding disorder. Other than Factor X, adsorption of Factor V and of von Willebrand factor have been reported in a number of series. In such cases, frequent infusion of the deficient factor can temporarily control bleeding [44]. An algorithm for diagnostic evaluation is seen in **Figure 2**.

## *2.2.4 Treatment of AL amyloidosis*

Management of AL amyloidosis is, in the first instance, management of endorgan dysfunction, with the goal to support the patient. However, definitive therapy requires eradication of the clone of B cells producing the immunoglobulin light chains that are misfolded and deposited as amyloid. Clinical trials have documented that the combination of the alkylating anti-neoplastic agent l-phenylalanine mustard (Melphalan) together with a potent corticosteroid such as Prednisone or Dexamethasone, can suppress production of new light chains, and, with adequate time, alter the balance of production and very slow degradation of AL amyloid. High dose Melphalan with autologous hematopoietic rescue was compared to conventional dose Melphalan plus dexamethasone in a prospective, randomized clinical trial published in 2007 [45]. That study reported inferior survival for patients randomized to high dose chemotherapy with autologous hematopoietic rescue (autologous transplant). However, in the past decade, the morbidity and mortality from autologous transplant has declined, and the risk-benefit ratio appears to have improved. An analysis by the Center for International Blood and Marrow Transplant Research (CIBMTR) published in 2015 reported that five-year overall survival following autologous transplant for AL amyloidosis had improved from 55% during the period of 1995–2000, to 77% in the time period from 2007 to 2012. Thus, outcome for transplant now appears superior to outcome from conventional dose anti-neoplastic therapy [46]. However, there have been no new prospective randomized clinical trials of autologous transplant versus non-transplant therapy. Newer therapies that are effective in reducing the burden of neoplastic plasma cells producing AL amyloid include proteasome inhibitors, and monoclonal antibodies that target plasma cells, such as daratumumab, an anti-CD38 monoclonal antibody. There are being studied, with promising results; however, no mature randomized data is available as of this writing from use of the agents. Anti-SAP antibody is a promising modality that appears to remove AL amyloid with relative efficiency; however, this agent remains investigational as of this writing [47].

#### **2.3 ATTR amyloidosis**

Hereditary transthyretin amyloidosis is an autosomal dominant, progressive, life-threatening disease caused by mutations in the gene encoding transthyretin. Transthyretin (TTR) is a homotetramer plasma transport protein secreted primarily by liver but also in retinal pigment epithelium and choroid plexus. It functions to transport thyroxine and retinol-binding protein and hence the name transthyretin [48]. ATTR amyloidosis results from deposition of abnormal TTR protein, which is a result of destabilized TTR-tetramer misfolding and fibril formation. ATTR

**13**

**Figure 2.**

*Diagnostic algorithm of systemic amyloidosis.*

amyloidosis can be hereditary or wild type. There are more the 130 mutations identified worldwide in the hereditary form with the most common being Val30Met mutation [49]. ATTR amyloidosis is a rare disease but recently it has been identified more commonly from advances in diagnostics. Wild type ATTR, occasionally called senile systemic amyloidosis because of the late age of onset is reported at an

incidence of 10% in people more than 80 years of age [50].

*The Clinical Spectrum of Amyloidosis*

*DOI: http://dx.doi.org/10.5772/intechopen.82763*

*The Clinical Spectrum of Amyloidosis DOI: http://dx.doi.org/10.5772/intechopen.82763*

*Amyloid Diseases*

nomenon of periorbital purpura [43].

*2.2.4 Treatment of AL amyloidosis*

Cutaneous AL amyloidosis is well described, and most often presents as either hemorrhagic bullous lesions, or, classically, as purpura or ecchymosis. Among the early classic descriptions of cutaneous manifestations of amyloidosis is the phe-

Patients with AL amyloidosis may have one or more acquired coagulopathies, resulting in a bleeding diathesis. This may be due to impaired synthesis of clotting proteins by a liver involved by amyloid infiltration; however, adsorption of coagulation proteins, most commonly Factor X, but other factors as well, results in increased clearance of coagulation proteins and a bleeding disorder. Other than Factor X, adsorption of Factor V and of von Willebrand factor have been reported in a number of series. In such cases, frequent infusion of the deficient factor can temporarily control bleeding [44]. An algorithm for diagnostic evaluation is seen in **Figure 2**.

Management of AL amyloidosis is, in the first instance, management of endorgan dysfunction, with the goal to support the patient. However, definitive therapy requires eradication of the clone of B cells producing the immunoglobulin light chains that are misfolded and deposited as amyloid. Clinical trials have documented that the combination of the alkylating anti-neoplastic agent l-phenylalanine mustard (Melphalan) together with a potent corticosteroid such as Prednisone or Dexamethasone, can suppress production of new light chains, and, with adequate time, alter the balance of production and very slow degradation of AL amyloid. High dose Melphalan with autologous hematopoietic rescue was compared to conventional dose Melphalan plus dexamethasone in a prospective, randomized clinical trial published in 2007 [45]. That study reported inferior survival for patients randomized to high dose chemotherapy with autologous hematopoietic rescue (autologous transplant). However, in the past decade, the morbidity and mortality from autologous transplant has declined, and the risk-benefit ratio appears to have improved. An analysis by the Center for International Blood and Marrow Transplant Research (CIBMTR) published in 2015 reported that five-year overall survival following autologous transplant for AL amyloidosis had improved from 55% during the period of 1995–2000, to 77% in the time period from 2007 to 2012. Thus, outcome for transplant now appears superior to outcome from conventional dose anti-neoplastic therapy [46]. However, there have been no new prospective randomized clinical trials of autologous transplant versus non-transplant therapy. Newer therapies that are effective in reducing the burden of neoplastic plasma cells producing AL amyloid include proteasome inhibitors, and monoclonal antibodies that target plasma cells, such as daratumumab, an anti-CD38 monoclonal antibody. There are being studied, with promising results; however, no mature randomized data is available as of this writing from use of the agents. Anti-SAP antibody is a promising modality that appears to remove AL amyloid with relative efficiency;

however, this agent remains investigational as of this writing [47].

Hereditary transthyretin amyloidosis is an autosomal dominant, progressive, life-threatening disease caused by mutations in the gene encoding transthyretin. Transthyretin (TTR) is a homotetramer plasma transport protein secreted primarily by liver but also in retinal pigment epithelium and choroid plexus. It functions to transport thyroxine and retinol-binding protein and hence the name transthyretin [48]. ATTR amyloidosis results from deposition of abnormal TTR protein, which is a result of destabilized TTR-tetramer misfolding and fibril formation. ATTR

**12**

**2.3 ATTR amyloidosis**

#### **Figure 2.**

*Diagnostic algorithm of systemic amyloidosis.*

amyloidosis can be hereditary or wild type. There are more the 130 mutations identified worldwide in the hereditary form with the most common being Val30Met mutation [49]. ATTR amyloidosis is a rare disease but recently it has been identified more commonly from advances in diagnostics. Wild type ATTR, occasionally called senile systemic amyloidosis because of the late age of onset is reported at an incidence of 10% in people more than 80 years of age [50].

#### *2.3.1 Clinical features of ATTR amyloidosis*

Phenotypically the ATTR results in clinical syndrome with respect to the organ involved. The three main clinical entities are polyneuropathy, cardiomyopathy and leptomeningeal disease. Fiber length-dependent neuropathy is pathognomonic of the disease. In the initial phase, small fiber neuropathy results in pain, paresthesia, allodynia, hyperalgesia, dysesthesia and impaired sensation to temperature. In later stages, large fiber dysfunction results in loss of vibration sense and balance, ultimately leading to difficulty with ambulation from progressive motor weakness [51]. Autonomic dysfunction results in orthostatic hypotension, neurogenic bladder, sexual dysfunction and gastrointestinal symptoms such as diarrhea and/or constipation [52]. Some patients with wild type ATTR develop carpel tunnel syndrome as their initial presentation and are also related to specific TTR mutations such as Leu58His, Ile84Ser and Tyr114His [53].

Familial amyloid cardiomyopathy occurs commonly with Val122Ile TTR mutation and they present with EKG abnormalities, heart failure, intractable arrhythmias and conduction abnormalities. Echocardiogram reveals a granular sparkling with ventricular and septal wall thickening [54]. MRI can show a classical late gadolinium enhancement but cardiac scintigraphy by Technetium-99 m pyrophosphate has the highest sensitivity and specificity in diagnosis [55]. Leptomeningeal amyloidosis occurs in patients with Asp18Gly, Ala25Thr and Tyr114Cys mutations. TTR protein is secreted by choroid plexus and gets deposited in cerebral and subarachnoid blood vessels and leptomeninges [49, 56]. Symptoms include transient ischemic attack, cerebral infarction or hemorrhage, subarachnoid hemorrhage, hydrocephalus, ataxia, spastic paralysis, convulsion, and dementia. Isolated leptomeningeal involvement is infrequent and occurs in patients harboring Val30Met mutation [57]. Ocular, renal and isolated gastrointestinal involvements are also reported in ATTR amyloidosis.

#### *2.3.2 Treatment of ATTR amyloidosis*

Once untreatable, hereditary ATTR amyloidosis is now primarily treated with liver transplantation, especially in Japan where it has shown better survival benefit and life expectancy. Liver transplantation is not widely practiced outside Japan due to low availability of living donors [58]. The transplantation replaces the abnormal TTR protein to a wild type protein. Overall studies have shown better outcomes in patients with early disease and Val30Met mutation compared to late onset and non-Val30Met patients. Leptomeningeal disease and retinal involvement do not improve by liver transplantation. Cardiac involvement continues to progress even after liver transplantation in some cases due to deposition of wild type ATTR.

Although liver transplantation has better outcome, not all patients are eligible due to advanced disease and multiple other sites of involvement. The tetramer destabilization is the initial step in the process of amyloid fibril formation and this was studied as a potential for treatment. Tafamidis, a benzoxazole derivative binds to thyroxine-binding sites of transthyretin and inhibits the dissociation of tetramers thereby blocking the rate-limiting step in monomer formation. In a randomized double-blinded phase II/III study in patients with polyneuropathy, Tafamidis did not meet the co-primary endpoints in the intention to treat population but did show significant improvement of neuropathy improvement score and quality of life in efficacy-evaluable population [59]. In another Phase III study for patients with ATTR related cardiomyopathy, Tafamidis was superior to placebo in decreasing the all-cause mortality and cardiovascular-related hospitalizations [60]. It is approved in both Europe and Japan for use in familial amyloid polyneuropathy and received

**15**

**Author details**

provided the original work is properly cited.

University of Connecticut, Farmington, CT, USA

\*Address all correspondence to: joharrison@uchc.edu

*The Clinical Spectrum of Amyloidosis*

*DOI: http://dx.doi.org/10.5772/intechopen.82763*

Neuropathy Impairment Score+7 [62].

TTRRx, an ASO specific to TTR mRNA [63].

FDA approval in the United States in 2018 for treatment of transthyretin cardiomyopathy. Difunisal, a nonsteroidal anti-inflammatory drug used to treat pain and osteoarthritis was studied as an agent to stabilize the amyloid tetramer. It functions by binding to the T4 binding site in TTR. In a phase II/III study it had significant improvement in neuropathy score in patients with amyloid polyneuropathy [61]. RNA interference is a phenomenon in which the gene expression is blocked by small RNA molecules. This approach has been studied in several diseases by introducing a small RNA into the cell and obscures a gene hence forth potentially inactivating the gene. Partisan is a RNA interference molecule developed to block production of abnormal TTR protein in liver. In a phase III trial, patients with hereditary transthyretin amyloidosis neuropathy received Partisan (dose 0.3 mg/kg

every 3 weeks) and had statistically significant improvement in modified

Antisense oligonucleotides (ASO) are chemically modified oligonucleotides designed to selectively bind the RNA in the cell and prevent the target protein expression by interfering with translation. A phase III trial is ongoing for ISIS-

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Aswanth Reddy, Enrique Ballesteros and Jonathan Scott Harrison\*

#### *The Clinical Spectrum of Amyloidosis DOI: http://dx.doi.org/10.5772/intechopen.82763*

*Amyloid Diseases*

*2.3.1 Clinical features of ATTR amyloidosis*

Leu58His, Ile84Ser and Tyr114His [53].

reported in ATTR amyloidosis.

*2.3.2 Treatment of ATTR amyloidosis*

Phenotypically the ATTR results in clinical syndrome with respect to the organ involved. The three main clinical entities are polyneuropathy, cardiomyopathy and leptomeningeal disease. Fiber length-dependent neuropathy is pathognomonic of the disease. In the initial phase, small fiber neuropathy results in pain, paresthesia, allodynia, hyperalgesia, dysesthesia and impaired sensation to temperature. In later stages, large fiber dysfunction results in loss of vibration sense and balance, ultimately leading to difficulty with ambulation from progressive motor weakness [51]. Autonomic dysfunction results in orthostatic hypotension, neurogenic bladder, sexual dysfunction and gastrointestinal symptoms such as diarrhea and/or constipation [52]. Some patients with wild type ATTR develop carpel tunnel syndrome as their initial presentation and are also related to specific TTR mutations such as

Familial amyloid cardiomyopathy occurs commonly with Val122Ile TTR mutation and they present with EKG abnormalities, heart failure, intractable arrhythmias and conduction abnormalities. Echocardiogram reveals a granular sparkling with ventricular and septal wall thickening [54]. MRI can show a classical late gadolinium enhancement but cardiac scintigraphy by Technetium-99 m pyrophosphate has the highest sensitivity and specificity in diagnosis [55]. Leptomeningeal amyloidosis occurs in patients with Asp18Gly, Ala25Thr and Tyr114Cys mutations. TTR protein is secreted by choroid plexus and gets deposited in cerebral and subarachnoid blood vessels and leptomeninges [49, 56]. Symptoms include transient ischemic attack, cerebral infarction or hemorrhage, subarachnoid hemorrhage, hydrocephalus, ataxia, spastic paralysis, convulsion, and dementia. Isolated leptomeningeal involvement is infrequent and occurs in patients harboring Val30Met mutation [57]. Ocular, renal and isolated gastrointestinal involvements are also

Once untreatable, hereditary ATTR amyloidosis is now primarily treated with liver transplantation, especially in Japan where it has shown better survival benefit and life expectancy. Liver transplantation is not widely practiced outside Japan due to low availability of living donors [58]. The transplantation replaces the abnormal TTR protein to a wild type protein. Overall studies have shown better outcomes in patients with early disease and Val30Met mutation compared to late onset and non-Val30Met patients. Leptomeningeal disease and retinal involvement do not improve by liver transplantation. Cardiac involvement continues to progress even after liver

Although liver transplantation has better outcome, not all patients are eligible due to advanced disease and multiple other sites of involvement. The tetramer destabilization is the initial step in the process of amyloid fibril formation and this was studied as a potential for treatment. Tafamidis, a benzoxazole derivative binds to thyroxine-binding sites of transthyretin and inhibits the dissociation of tetramers thereby blocking the rate-limiting step in monomer formation. In a randomized double-blinded phase II/III study in patients with polyneuropathy, Tafamidis did not meet the co-primary endpoints in the intention to treat population but did show significant improvement of neuropathy improvement score and quality of life in efficacy-evaluable population [59]. In another Phase III study for patients with ATTR related cardiomyopathy, Tafamidis was superior to placebo in decreasing the all-cause mortality and cardiovascular-related hospitalizations [60]. It is approved in both Europe and Japan for use in familial amyloid polyneuropathy and received

transplantation in some cases due to deposition of wild type ATTR.

**14**

FDA approval in the United States in 2018 for treatment of transthyretin cardiomyopathy. Difunisal, a nonsteroidal anti-inflammatory drug used to treat pain and osteoarthritis was studied as an agent to stabilize the amyloid tetramer. It functions by binding to the T4 binding site in TTR. In a phase II/III study it had significant improvement in neuropathy score in patients with amyloid polyneuropathy [61].

RNA interference is a phenomenon in which the gene expression is blocked by small RNA molecules. This approach has been studied in several diseases by introducing a small RNA into the cell and obscures a gene hence forth potentially inactivating the gene. Partisan is a RNA interference molecule developed to block production of abnormal TTR protein in liver. In a phase III trial, patients with hereditary transthyretin amyloidosis neuropathy received Partisan (dose 0.3 mg/kg every 3 weeks) and had statistically significant improvement in modified Neuropathy Impairment Score+7 [62].

Antisense oligonucleotides (ASO) are chemically modified oligonucleotides designed to selectively bind the RNA in the cell and prevent the target protein expression by interfering with translation. A phase III trial is ongoing for ISIS-TTRRx, an ASO specific to TTR mRNA [63].
