AA amyloidosis | |
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Specialty | Rheumatology |
AA amyloidosis is a form of amyloidosis, a disease characterized by the abnormal deposition of fibers of insoluble protein in the extracellular space of various tissues and organs. In AA amyloidosis, the deposited protein is serum amyloid A protein (SAA), an acute-phase protein which is normally soluble and whose plasma concentration is highest during inflammation. [1]
AA amyloidosis is a complication of a number of inflammatory diseases and infections, [2] although only a small portion of patients with these conditions will go on to develop AA amyloidosis. The most common presentation of AA amyloidosis is renal in nature, including proteinuria, nephrotic syndrome and progressive development of chronic kidney disease leading to end stage kidney disease (ESKD) and need for renal replacement therapy (e.g. dialysis or kidney transplantation). [3] A natural history study of AA amyloidosis patients reported a number of conditions associated with AA amyloidosis: [1]
Signs and symptoms of amyloidosis can vary depending on the affected organ. AA amyloidosis commonly affects kidneys, liver, and stomach. [13]
In a healthy individual, the median plasma concentration of SAA is 3 mg per liter. [14] This can increase to over 2000 mg per liter during an acute phase response and a sustained overproduction of SAA is required for the creation of the AA deposits that define AA amyloidosis. [15] High levels of SAA, however, is not a sufficient condition for the development of systemic AA amyloidosis and it remains unclear what triggers the accumulation of AA. [16]
The AA protein is mainly deposited in the liver, spleen and kidney, and AA amyloidosis can lead to nephrotic syndrome and ESRD. [17] [18] Natural history studies show, however, that it is the kidney involvement that drives the progression of the disease. In general, old age, reduced serum albumin concentration, end stage kidney failure, and sustained elevated SAA concentration are all associated with poor prognosis. [19]
Tissue biopsy using subcutaneous abdominal fat tissue aspiration is typically used as it is safe and sensitive. It is also possible to biopsy the rectal mucosa or minor salivary glands. Amyloidosis is confirmed by histological identification of amyloid deposits. At this point, amyloid typing with immunochemical staining is necessary, as the differential diagnosis includes AA amyloidosis, AL amyloidosis, hereditary amyloidosis, dialysis-related amyloidosis and age-related systemic amyloidosis. Testing of serum and urine for monoclonal immunoglobulins and of serum for free light chains may help rule out immunoglobulin light chain amyloidosis, while genetic testing may be used if hereditary amyloidosis is suspected. [20]
There are currently no approved treatments for systemic AA amyloidosis. [17] The current standard of care includes treatments for the underlying inflammatory disease with anti-inflammatory drugs, immunosuppressive agents or biologics. AA amyloidosis patients are also receiving treatments to slow down the decline of their renal function, such as angiotensin II receptor blockers or angiotensin converting enzyme inhibitors. [21]
There is evidence that eating amyloid fibers may lead to amyloidosis. This evidence is based on studies in cattle, chickens, mice, and cheetahs. [22] Thus, in a sense, SAA amyloidosis may be considered a contagious disease, although whether this occurs or is important in the development of naturally occurring amyloidosis remains unknown. Nevertheless, because amyloid fibers can be detected in muscle in low amounts, it raises some concern about whether people could develop amyloidosis as a result of ingesting meat from an animal with the disease. [22]
Nephrology is a specialty for both adult internal medicine and pediatric medicine that concerns the study of the kidneys, specifically normal kidney function and kidney disease, the preservation of kidney health, and the treatment of kidney disease, from diet and medication to renal replacement therapy. The word "renal" is an adjective meaning "relating to the kidneys", and its roots are French or late Latin. Whereas according to some opinions, "renal" and "nephro" should be replaced with "kidney" in scientific writings such as "kidney medicine" or "kidney replacement therapy", other experts have advocated preserving the use of renal and nephro as appropriate including in "nephrology" and "renal replacement therapy", respectively.
Proteinuria is the presence of excess proteins in the urine. In healthy persons, urine contains very little protein, less than 150 mg/day; an excess is suggestive of illness. Excess protein in the urine often causes the urine to become foamy. Severe proteinuria can cause nephrotic syndrome in which there is worsening swelling of the body.
Nephrotic syndrome is a collection of symptoms due to kidney damage. This includes protein in the urine, low blood albumin levels, high blood lipids, and significant swelling. Other symptoms may include weight gain, feeling tired, and foamy urine. Complications may include blood clots, infections, and high blood pressure.
Kidney failure, also known as end-stage renal disease (ESRD), is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as either acute kidney failure, which develops rapidly and may resolve; and chronic kidney failure, which develops slowly and can often be irreversible. Symptoms may include leg swelling, feeling tired, vomiting, loss of appetite, and confusion. Complications of acute and chronic failure include uremia, hyperkalemia, and volume overload. Complications of chronic failure also include heart disease, high blood pressure, and anaemia.
Amyloidosis is a group of diseases in which abnormal proteins, known as amyloid fibrils, build up in tissue. There are several non-specific and vague signs and symptoms associated with amyloidosis. These include fatigue, peripheral edema, weight loss, shortness of breath, palpitations, and feeling faint with standing. In AL amyloidosis, specific indicators can include enlargement of the tongue and periorbital purpura. In wild-type ATTR amyloidosis, non-cardiac symptoms include: bilateral carpal tunnel syndrome, lumbar spinal stenosis, biceps tendon rupture, small fiber neuropathy, and autonomic dysfunction.
Kidney disease, or renal disease, technically referred to as nephropathy, is damage to or disease of a kidney. Nephritis is an inflammatory kidney disease and has several types according to the location of the inflammation. Inflammation can be diagnosed by blood tests. Nephrosis is non-inflammatory kidney disease. Nephritis and nephrosis can give rise to nephritic syndrome and nephrotic syndrome respectively. Kidney disease usually causes a loss of kidney function to some degree and can result in kidney failure, the complete loss of kidney function. Kidney failure is known as the end-stage of kidney disease, where dialysis or a kidney transplant is the only treatment option.
Membranous glomerulonephritis (MGN) is a slowly progressive disease of the kidney affecting mostly people between ages of 30 and 50 years, usually white people.
Nephritic syndrome is a syndrome comprising signs of nephritis, which is kidney disease involving inflammation. It often occurs in the glomerulus, where it is called glomerulonephritis. Glomerulonephritis is characterized by inflammation and thinning of the glomerular basement membrane and the occurrence of small pores in the podocytes of the glomerulus. These pores become large enough to permit both proteins and red blood cells to pass into the urine. By contrast, nephrotic syndrome is characterized by proteinuria and a constellation of other symptoms that specifically do not include hematuria. Nephritic syndrome, like nephrotic syndrome, may involve low level of albumin in the blood due to the protein albumin moving from the blood to the urine.
Congenital nephrotic syndrome is a rare kidney disease which manifests in infants during the first 3 months of life, and is characterized by high levels of protein in the urine (proteinuria), low levels of protein in the blood, and swelling. This disease is primarily caused by genetic mutations which result in damage to components of the glomerular filtration barrier and allow for leakage of plasma proteins into the urinary space.
Leukocyte cell-derived chemotaxin-2 (LECT2) is a protein first described in 1996 as a chemotactic factor for neutrophils, i.e. it stimulated human neutrophils to move directionally in an in vitro assay system. The protein was detected in and purified from cultures of Phytohaemagglutinin-activated human T-cell leukemia SKW-3 cells. Subsequent studies have defined LECT2 as a hepatokine, i.e. a substance made and released into the circulation by liver hepatocyte cells that regulates the function of other cells: it is a hepatocyte-derived, hormone-like, signaling protein.
In hematology, plasma cell dyscrasias are a spectrum of progressively more severe monoclonal gammopathies in which a clone or multiple clones of pre-malignant or malignant plasma cells over-produce and secrete into the blood stream a myeloma protein, i.e. an abnormal monoclonal antibody or portion thereof. The exception to this rule is the disorder termed non-secretory multiple myeloma; this disorder is a form of plasma cell dyscrasia in which no myeloma protein is detected in serum or urine of individuals who have clear evidence of an increase in clonal bone marrow plasma cells and/or evidence of clonal plasma cell-mediated tissue injury. Here, a clone of plasma cells refers to group of plasma cells that are abnormal in that they have an identical genetic identity and therefore are descendants of a single genetically distinct ancestor cell.
Amyloid light-chain (AL) amyloidosis, also known as primary amyloidosis, is the most common form of systemic amyloidosis. The disease is caused when a person's antibody-producing cells do not function properly and produce abnormal protein fibers made of components of antibodies called light chains. These light chains come together to form amyloid deposits which can cause serious damage to different organs. An abnormal light chain in urine is known as Bence Jones protein.
Haemodialysis-associated amyloidosis is a form of systemic amyloidosis associated with chronic kidney failure. Amyloidosis is the accumulation of misfolded protein fibers in the body that can be associated with many chronic illnesses. Even though amyloidosis is common in chronic kidney disease (CKD) patients receiving chronic regular dialysis, it has also been reported in a patient with chronic kidney failure but who never received dialysis.
Mesangial proliferative glomerulonephritis (MesPGN) is a morphological pattern characterized by a numerical increase in mesangial cells and expansion of the extracellular matrix within the mesangium of the glomerulus. The increase in the number of mesangial cells can be diffuse or local and immunoglobulin and/or complement deposition can also occur. MesPGN is associated with a variety of disease processes affecting the glomerulus, though can be idiopathic. The clinical presentation of MesPGN usually consists of hematuria or nephrotic syndrome. Treatment is often consistent with the histologic pattern of and/or disease process contributing to mesangial proliferative glomerulonephritis, and usually involves some form of immunosuppressant.
Glomerulonephrosis is a non-inflammatory disease of the kidney (nephrosis) presenting primarily in the glomerulus as nephrotic syndrome. The nephron is the functional unit of the kidney and it contains the glomerulus, which acts as a filter for blood to retain proteins and blood lipids. Damage to these filtration units results in important blood contents being released as waste in urine. This disease can be characterized by symptoms such as fatigue, swelling, and foamy urine, and can lead to chronic kidney disease and ultimately end-stage renal disease, as well as cardiovascular diseases. Glomerulonephrosis can present as either primary glomerulonephrosis or secondary glomerulonephrosis.
Free light chains (FLCs) are immunoglobulin light chains that are found in the serum (blood) in an unbound (free) state. In recent decades, measuring the amount of free light chains (FLCs) in the blood has become a practical clinical test. FLC tests can be used to diagnose and monitor diseases like multiple myeloma and amyloidosis.
Onconephrology is a specialty in nephrology that deals with the study of kidney diseases in cancer patients. A nephrologist who takes care of patients with cancer and kidney disease is called an onconephrologist. This branch of nephrology encompasses nephrotoxicity associated with existing and novel chemotherapeutics, kidney disease as it pertains to stem cell transplant, paraneoplastic kidney disorders, paraproteinemias, electrolyte disorders associated with cancer, and more as discussed below.
LECT2 Amyloidosis (ALECT2) is a form of amyloidosis caused by the LECT2 protein. It was found to be the third most common cause of amyloidosis in a set of more than 4,000 individuals studied at the Mayo Clinic; the first and second most common forms the disorder were AL amyloidosis and AA amyloidosis, respectively. Amyloidosis is a disorder in which the abnormal deposition of a protein in organs and/or tissues gradually leads to organ failure and/or tissue injury.
Monoclonal immunoglobulin deposition disease, or MIDD, is a disease characterised by the deposition of monoclonal immunoglobulins on the basement membrane of the kidney. Monoclonal immunoglobulins are produced by monoclonal plasma cells, which are found in a variety of plasma cell dyscrasias. The deposition of monoclonal immunoglobulins on the basement membrane of the kidney causes renal impairment. As well as the kidney, MIDD may also affect the liver, heart, peripheral nerves, lung and skin.
Monoclonal gammopathy of renal significance (MGRS) are a group of kidney disorders that present with kidney damage due to nephrotoxic monoclonal immunoglobulins secreted by clonal plasma cells or B cells. By definition, people with MGRS do not meet criteria for multiple myeloma or other hematologic malignancies. The term MGRS was introduced in 2012 by the International Kidney and Monoclonal Gammopathy Research Group (IKMG). MGRS is associated with monoclonal gammopathy of undetermined significance (MGUS). People with MGUS have a monoclonal gammopathy but does not meet the criteria for the clonal burden nor the presence of end organ damage seen in hematologic malignancies. In a population based study based on the NHANES III health survey; 6% of patients with MGUS were subsequently classified as having MGRS. The prevalence and incidence of MGRS in the general population or in specific populations is not known but it is more prevalent in those over the age of 50 as there is a monoclonal protein (M-protein) present in 3% of those 50 and years older and 5% of those 70 years and older, placing those 50 and older at increased risk of MGRS.