**2.1 AA amyloidosis**

Worldwide, AA amyloidosis is the most common type of systemic amyloidosis. Although AA amyloid currently is the most common form of amyloidosis, the incidence is decreasing over time in western countries. This has been attributed to a significant decrease in chronic infections, as well as improved therapies for

**5**

**Table 2.**

treatment.

nized as a cause of AA amyloidosis.

Cryopyrin-associated periodic syndromes

TNF-receptor–associated periodic fever

Rheumatoid arthritis (RA) Alzheimer's disease Juvenile idiopathic arthritis Ankylosing spondylitis Psoriasis and psoriatic arthritis

Still disease [67] Behçet syndrome [68] Familial Mediterranean fever

Crohn's disease Castleman disease [69]

(CAPS) [70]

syndrome Vasculitis

*Causes of AA amyloidosis.*

*The Clinical Spectrum of Amyloidosis*

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

inflammatory diseases. A review from the UK in 2013 estimated in excess of 8.0 per million cases of amyloidosis every year and AA being second most common (18%) [1]. The underlying causes of systemic AA amyloidosis include a wide range of inflammatory diseases, including but not limited to chronic inflammatory disorders, infections, and malignancy (**Table 2**). The amyloid fibril AA is most often a result of abnormal folding and aggregation of serum apolipoprotein A (SAA), which is an acute phase reactant—that is, the level becomes elevated in the blood in response to inflammation [2]. AA amyloid fibrils form through a process of cleavage, misfolding, and aggregation into a highly ordered abnormal β-sheet conformation. Amyloid fibrils associate anatomically with other moieties, including glycosaminoglycans and serum amyloid P component (SAP), forming deposits that

In the healthy, physiological state in humans, the serum SAA concentration is relatively low, but the level increases about a thousand fold during an inflammatory reaction. In humans, SAA is expressed in three different isoforms: SAA1, SAA2 and SAA4 and are encoded by different genes. SAA1 and SAA2 are solely expressed in liver and are entirely bound to plasma High Density Lipoprotein in plasma [4]. Inflammation increases the secretion of cytokines, including IL-1, IL-6 and TNF, which in turn increases the production of SAA [5]. SAA functions to transport and recycle cholesterol from sites of tissue injury, thereby modulating the immune response. Not all individuals with high SAA levels develop amyloidosis; it appears that certain polymorphisms and mutations in the SAA genes predispose to abnormal protein folding and therefore amyloid formation [6]. The formation of amyloid fibril from precursor SAA protein is the result of complex interaction with glycosaminoglycans, including most prominently heparan sulfate [7]. Impairing this interaction or the degrading of heparan sulfate by a heparinase has been shown to prevent formation of amyloid fibrils, and this has led to an area of research for potential

More recently, a protein named A Leukocyte Chemotactic factor 2 (ALECT2) protein has been shown to be a cause of AA amyloidosis, with a propensity to cause renal amyloidosis [8]. The human ALECT2 gene, discovered only in 2008, has been localized to chromosome 5 (5q31.1-q32) [9]. ALECT2 is being increasingly recog-

Inherited forms of AA amyloidosis arise due to mutations in a variety of proteins that can undergo abnormal folding and consequent deposition into tissues,

**Chronic disorders [64–66] Infections Malignancy [74]**

[73]

Leprosy [71] Osteomyelitis Tuberculosis [72] Chronic bronchiectasis Hodgkin disease Non-Hodgkin lymphoma Renal cell carcinoma Gastrointestinal cancers Lung cancer [75] Urogenital carcinoma Mesothelioma [76]

disrupt the structure and function of tissues and organs [3].

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

*Amyloid Diseases*

patient (see **Table 1**).

**Figure 1.**

Fatigue

Diarrhea

**Table 1.**

particular amyloid protein as "Amyloid Protein AX," where the X is a suffix to the designation, based on the identity of the amyloid protein. The more commonly encountered subtypes are, for example Amyloid Protein AL, Amyloid Protein AA, and Amyloid Protein ATTR, as discussed below. This chapter is an overview of the different categories of amyloidosis, with a focus on the clinical features, prognosis, and management of focal or systemic amyloidosis. Symptoms depend on the type and amount of amyloid protein, and are often variable. The manifestations depend on the identity of the underlying protein that forms the amyloid fibrils, the burden of amyloid, and the organs involved, as well as comorbidities of an individual

*Photomicrographs of a lymph node biopsy with AL amyloidosis. Panel A: 10× magnification of a left axillary lymph node biopsy stained using Hematoxylin and Eosin, demonstrating amorphous pink material typical of amyloid infiltration. White areas are fat that has been leached from the tissue in processing. Panel B: 10×* 

*magnification of the same lymph node stained using Congo red, viewed by light microscopy.*

Edema at one or more sites (due to either heart failure, nephrotic syndrome, or both)

Purpura (due to either coagulation disorder, skin fragility due to amyloid infiltration, or both)

Lightheadedness upon standing (due to orthostatic hypotension)

Orthostatic hypotension (due to autonomic nerve dysfunction)

**4**

**2. Types of systemic amyloidosis**

*Symptoms commonly seen in systemic amyloidosis*

Focal pain (due to peripheral neuropathy) *Physical signs commonly seen in systemic amyloidosis*

Focal mass lesions (amyloid deposition focally)

Edema at one or more sites

enlarged tongue (macroglossia)

*Clinical manifestation of systemic amyloidosis.*

Worldwide, AA amyloidosis is the most common type of systemic amyloidosis.

Although AA amyloid currently is the most common form of amyloidosis, the incidence is decreasing over time in western countries. This has been attributed to a significant decrease in chronic infections, as well as improved therapies for

**2.1 AA amyloidosis**

inflammatory diseases. A review from the UK in 2013 estimated in excess of 8.0 per million cases of amyloidosis every year and AA being second most common (18%) [1]. The underlying causes of systemic AA amyloidosis include a wide range of inflammatory diseases, including but not limited to chronic inflammatory disorders, infections, and malignancy (**Table 2**). The amyloid fibril AA is most often a result of abnormal folding and aggregation of serum apolipoprotein A (SAA), which is an acute phase reactant—that is, the level becomes elevated in the blood in response to inflammation [2]. AA amyloid fibrils form through a process of cleavage, misfolding, and aggregation into a highly ordered abnormal β-sheet conformation. Amyloid fibrils associate anatomically with other moieties, including glycosaminoglycans and serum amyloid P component (SAP), forming deposits that disrupt the structure and function of tissues and organs [3].

In the healthy, physiological state in humans, the serum SAA concentration is relatively low, but the level increases about a thousand fold during an inflammatory reaction. In humans, SAA is expressed in three different isoforms: SAA1, SAA2 and SAA4 and are encoded by different genes. SAA1 and SAA2 are solely expressed in liver and are entirely bound to plasma High Density Lipoprotein in plasma [4]. Inflammation increases the secretion of cytokines, including IL-1, IL-6 and TNF, which in turn increases the production of SAA [5]. SAA functions to transport and recycle cholesterol from sites of tissue injury, thereby modulating the immune response. Not all individuals with high SAA levels develop amyloidosis; it appears that certain polymorphisms and mutations in the SAA genes predispose to abnormal protein folding and therefore amyloid formation [6]. The formation of amyloid fibril from precursor SAA protein is the result of complex interaction with glycosaminoglycans, including most prominently heparan sulfate [7]. Impairing this interaction or the degrading of heparan sulfate by a heparinase has been shown to prevent formation of amyloid fibrils, and this has led to an area of research for potential treatment.

More recently, a protein named A Leukocyte Chemotactic factor 2 (ALECT2) protein has been shown to be a cause of AA amyloidosis, with a propensity to cause renal amyloidosis [8]. The human ALECT2 gene, discovered only in 2008, has been localized to chromosome 5 (5q31.1-q32) [9]. ALECT2 is being increasingly recognized as a cause of AA amyloidosis.

Inherited forms of AA amyloidosis arise due to mutations in a variety of proteins that can undergo abnormal folding and consequent deposition into tissues,


#### **Table 2.** *Causes of AA amyloidosis.*

#### *Amyloid Diseases*

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 somewhat peculiar to the specific etiology of the inherited disorder.

#### *2.1.1 Clinical features of systemic AA amyloidosis*

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].

#### *2.1.2 Treatment*

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 shown to reverse organ function.

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 FMF [14].

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

**7**

*The Clinical Spectrum of Amyloidosis*

**2.2 AL amyloidosis**

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

intestinal involvement by AA amyloid [17].

potential for future management of amyloidosis.

phase III trial did not meet the targeted endpoints, and so Eporsidate has not been developed further to date [16]. Dimethyl sulfoxide (DMSO) is a derivative of intercellular low-density lipoprotein, which reduces levels of acute phase reactants including SAA, and has been shown to improve symptoms in patients with gastro-

Anti-SAP antibody, R-1-[6-[R-2-carboxy-pyrrolidin-1-yl]-6-oxo-hexanoyl] pyrrolidine-2-carboxylic acid (CPHPC) was studied in Al and AA amyloidosis with favorable responses in an open label study [18]. A recent phase Ib trial of SAP inhibitor, Miridesap followed by humanized monoclonal antibody Dezamizumab against SAP showed clearance of amyloid fibrils in liver and spleen, confirmed by I-SAP scintigraphy [19]. Further studies are ongoing and these treatments are a real

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 amyloi-

dosis accounted for only 2.2% of all patients with systemic amyloidosis [26].

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

phase III trial did not meet the targeted endpoints, and so Eporsidate has not been developed further to date [16]. Dimethyl sulfoxide (DMSO) is a derivative of intercellular low-density lipoprotein, which reduces levels of acute phase reactants including SAA, and has been shown to improve symptoms in patients with gastrointestinal involvement by AA amyloid [17].

Anti-SAP antibody, R-1-[6-[R-2-carboxy-pyrrolidin-1-yl]-6-oxo-hexanoyl] pyrrolidine-2-carboxylic acid (CPHPC) was studied in Al and AA amyloidosis with favorable responses in an open label study [18]. A recent phase Ib trial of SAP inhibitor, Miridesap followed by humanized monoclonal antibody Dezamizumab against SAP showed clearance of amyloid fibrils in liver and spleen, confirmed by I-SAP scintigraphy [19]. Further studies are ongoing and these treatments are a real potential for future management of amyloidosis.
