**3. Major types of amyloidosis**

The most recent classification of amyloidosis has been published by the Nomenclature Committee of the International Society of Amyloidosis (ISA) in 2016. The classification listed 36 different extracellular fibril proteins seen in humans and animals, whose sequence is identified unequivocally (**Table 1**). According to this scheme, amyloid proteins can be broadly divided into systemic or localized in relation to the extent of organ involved by the condition. Systemic forms of amyloidosis are common and may result in serious clinical consequences, while localized forms tend to be less common and clinically indolent unless they involve critical organs such as CNS. Therefore, the distinction between the two is important.


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*Pathologic Findings of Amyloidosis: Recent Advances DOI: http://dx.doi.org/10.5772/intechopen.84268*

**3.1 Amyloid light chain (AL) protein**

associated with monoclonal plasma cell disorder [3].

**3.2 Amyloid-associated type (AA) protein**

and gastrointestinal tract can be affected [4].

**3.3 Transthyretin amyloid (ATTR) protein**

guishing two types in early stage is important.

Exhaustive review of every subtype is beyond the scope of this chapter. The more

AL type amyloid is the most common amyloid in the United States. The AL chain is a clonal immunoglobulin light chain or light chain fragment, which is produced by the uncontrolled productions of antibodies by plasma cells. Lambda (λ) type (ALλ) is more common than kappa (κ) type (ALκ) light chain. This type of amyloidosis is related to monoclonal plasma cell disorders, especially multiple myeloma or other B-lymphocyte-related disorders. If we cannot determine AL type amyloidosis to a certain disease, it is categorized as primary amyloidosis. Even if we cannot demonstrate a specific disease to AL type amyloidosis, we still see monoclonal plasma cell proliferation in these patients. In either case, we can find immunoglobulin or light chain within the serum or urine. The most commonly affected organ is the kidney. The heart, peripheral nervous system, gastrointestinal tract, and respiratory tract can also be affected. A localized form of AL type amyloid can be seen in the gastrointestinal tract [2]. Amyloid heavy chain (AH) is rarely reported but also

AA type amyloidosis is the most common amyloid worldwide. AA type amyloid

TTR is a transport protein made in the liver and choroid plexus. TTR transfers thyroxin and retinol in the blood and cerebrospinal fluid. TTR proteins can be differentiated into wild type and mutant type. TTR wild-type amyloid is associated with systemic senile amyloidosis and mostly affects heart ventricles in elderly patients. In this population, a prevalence of monoclonal gammopathy of undetermined significance (MGUS) has been reported [5]. TTR mutant type protein is related to hereditary amyloidosis. TTR mutant type protein can affect commonly peripheral nerves and other organs including the heart and gastrointestinal tract. This is inherited as an autosomal dominant pattern. The clinical course of TTR mutant type is relatively faster than TTR wild type in terms of onset and progression. Also, treatment and prognosis of two types are different. Therefore, distin-

is an acute phase protein derived from SAP by proteolysis. AA type amyloid is made in the liver, bounds to high-density lipoprotein (HDL), and is associated with chronic inflammatory disorder. In the past, the primary cause was predominantly of infections such as tuberculosis and chronic osteomyelitis. Nowadays, with the development of antibiotics, the most common source of AA type amyloid has become noninfectious inflammatory conditions, such as rheumatoid arthritis or inflammatory bowel diseases including Crohn's disease and ulcerative colitis. Typical organs of AA type amyloid deposition are the kidney, liver, and spleen. AA type amyloidosis is also related to hereditary amyloidosis, caused by familial Mediterranean fever inherited as an autosomal recessive pattern. This is an autoinflammatory disorder characterized by frequent fever and serosal inflammation. The main affected organ is the kidney, but other organs such as the heart, spleen,

common and clinically important types of amyloid protein are described below.

#### **Table 1.**

*Amyloid fibril protein classification and associated disease.*

Exhaustive review of every subtype is beyond the scope of this chapter. The more common and clinically important types of amyloid protein are described below.
