Leucocyte cell-derived chemotaxin 2 related amyloidosis
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Synonyms and keywords:LECT2 amyloidosis

# Overview
Amyloidosis derived from leukocyte cellderived chemotaxin 2 is a recently recognized form of amyloidosis, and it has already been established as a frequent form of systemic amyloidosis in the United States, with predominant involvement of kidney and liver. The disease has a strong ethnic bias, affecting mainly Hispanics (particularly Mexicans). Additional ethnic groups prone to develop amyloidosis derived from leukocyte cellderived chemotaxin 2 include Punjabis (native to India and Pakistan), First Nations people in British Columbia, and Native Americans. Most patients are elderly who present with chronic renal insufficiency and bland urinary sediment. Proteinuria is variable, being absent altogether in about one third of patients. Liver involvement is frequently an incidental finding. Amyloidosis derived from leukocyte cellderived chemotaxin 2 deposits shows a characteristic distribution: in the kidney, there is consistent involvement of cortical interstitium, whereas in the liver, there is a preferential involvement of periportal and pericentral vein regions. Concurrent renal disease is frequent, with diabetic nephropathy and IgA nephropathy being the most common. Patient survival is excellent, likely because of the rarity of cardiac involvement, whereas renal survival is guarded, with a median renal survival of 62 months in those without concurrent renal disease. There is currently no efficacious therapy for amyloidosis derived from leukocyte cellderived chemotaxin 2 amyloidosis. Renal transplantation seems to be a reasonable treatment for patients with advanced renal failure, although the disease may recur in the allograft. The pathogenesis of amyloidosis derived from leukocyte cellderived chemotaxin 2 amyloidosis has not yet been elucidated. It could be a result of leukocyte cellderived chemotaxin 2 overexpression by hepatocytes either constitutively (controlled by yet-uncharacterized genetic defects) or secondary to hepatocellular damage. It is critical not to misdiagnose amyloidosis derived from leukocyte cellderived chemotaxin 2 amyloidosis as Immunoglobulin light chain-derived amyloidosis to avoid harmful chemotherapy..

# Historical Perspective
- The first case of ALECT2 was discovered by Benson et al in 2008.

# Pathophysiology
- The pathogenesis of this disease is related to accumulation of a protein called LECT2.
- LECT2 protein is a multi functional factor involved in
Chemotaxis
Inflammation
Immunomodulation
Damage/repair process.
- Chemotaxis
- Inflammation
- Immunomodulation
- Damage/repair process.
- LECT2 is synthesized mainly by hepatocytes but also expressed in many organs, including vascular endothelial cells, smooth muscle cells, adipocytes, and epithelial cells such as renal tubular epithelial cells.
- According to the literature, ALECT2 involves G/A polymorphism affecting nucleotide 172 in exon 3 of the LECT2 protein.
- Substitution of the isoleucine with valine at position 40 makes the protein unstable imparting an amyloidogenic property to the LECT2 protein.
- Alternately the disease could be due to interference in the LECT2 catabolic pathway or LECT2 transport.
- Possibly resulting from a genetic defect which ultimately results in an increased local tissue concentration of LECT2 leading to amyloid fibril formation.
- The kidney is the primary target of this disease. '
- Other common organs involved other than the kidney include liver, spleen, prostate, gastrointestinal tract, peripheral nervous system, and lungs.
- Cardiac involvement never occurs, which gives this disease a survival advantage compared to other forms of amyloidosis.
- Other organs which are not involved include brain, pancreas, and fibroadipose tissue.

## Histopathology

### Kidney
- Histologically, renal ALECT2 amyloidosis involves diffuse cortical interstitium.
- The glomerular and vascular amyloid deposits are variable.
- ALECT2 deposits stain strongly positive with Congo red and demonstrates apple-green birefringence, under polarized light.
- Immunofluorescence is usually negative.
- A minority of patients may demonstrate false-positive staining for serum amyloid A (SAA).

### Liver
- ALECT2 deposits in the liver have a characteristic histologic morphology.
- ALECT2 deposits are seen preferentially surrounding the central veins and in the periphery of portal tracts.
- Exhibits a distinctive globular appearance.

# Natural History, Complications, and Prognosis
- Patient survival in ALECT2 amyloidosis is significantly better than that of AL amyloidosis and AA amyloidosis, likely because of the rarity or absence of cardiac involvement in ALECT2 amyloidosis.
- In a series of 72 patients with renal ALECT2 amyloidosis, only 6% of 64 patients with available data died after a median follow-up of 22 months.
- The renal survival, however, is guarded; 39% of patients in the above-mentioned study progressed to ESRD .
- Independent predictors of renal survival in renal ALECT2 amyloidosis without concurrent kidney disease on biopsy were serum creatinine at diagnosis, with a value of 2.0 mg/dl being the best cutoff for predicting ESRD, degree of glomerulosclerosis, and presence of diabetes
- Renal amyloid load and degree of proteinuria did not predict outcome

# Diagnosis

## History
- ALECT2 amyloidosis mainly affects the older population.
- Patients with kidney involvement are slightly older at diagnosis (median age of 69 years old) than those with liver involvement (median age of 61 years old)

## Symptoms
Common symptoms of LECT2 amyloidosis include:

## Laboratory Findings
- Typing amyloid deposits by LC/MS-based proteomics is currently the best tool to diagnose ALECT2 amyloidosis and other forms of amyloidosis because of its high sensitivity and specificity and because it is a single test that can detect the culprit protein in contrast to IHC typing of amyloidosis, which requires staining for multiple antibodies using several tissue sections (6,50,51).
- LECT2 protein has many lysine and arginine residues and therefore, can readily be digested by trypsin into peptides, and the amino acid sequence of the peptides can be determined by LC/MS.
- The diagnosis of ALECT2 amyloidosis by LC/MS is made according to clinically established criteria by identification of LECT2 peptide spectra and amyloid-associated proteins (serum amyloid P  and apoE).
- Because plasma concentration of LECT2 is trivial, contamination of amyloid deposits by serum LECT2 is not an issue, and the diagnosis is usually straightforward. Unfortunately, clinical amyloid typing by proteomics is available only in few selected centers, such as the Mayo Clinic.
- There are now several commercially available antibodies for IHC detection of LECT2 that seem to be highly sensitive however, weak false-positive staining may occur , which may result from aggressive antigen retrieval. Therefore, it is crucial that LECT2 antibody is carefully validated and optimized for the diagnosis of ALECT2.
- In cases that exhibit only weak staining for LECT2, false-positive staining for SAA, or staining for Ig light or heavy chains by immunofluorescence or immunoperoxidase, confirmation by LC/MS is strongly recommended.
- When amyloid typing is performed by IHC, it is critical that the testing is done with a panel of antibodies against several types of amyloidosis, so-called comparative IHC, instead of staining for a single precursor protein.
- In general, better results are obtained if amyloid typing by IHC is performed in specialized laboratories.
- Of note, monoclonal gammopathy of undetermined significance was present in 10% and 8% of patients reported by Said et al.  and Larsen et al. respectively, highlighting the importance of accurate typing of amyloid deposits to avoid misdiagnosing ALECT2 amyloidosis as AL amyloidosis

# Treatment

## Medical Therapy
- There is currently no specific therapy for ALECT2 amyloidosis.
- Because the precursor protein is normal (nonmutant) LECT2, liver transplantation probably is not effective, although this approach has not been tested.
- Preliminary data suggest that renal transplantation is a reasonable therapeutic option for patients with advanced renal failure. I
- In one recent series, the disease recurred in one of five patients transplanted, but the short-term outcome was good: after a mean duration of 20 months of post-transplant follow-up, no patient had graft loss, and two patients had normal final serum creatinine.
- Some potential future therapies for ALECT2 amyloidosis include reducing the supply of LECT2 (such as by Wnt/-catinin signaling pathway inhibitors, etinoids, exisulind, and endostatin), inhibiting fibrillogenesis (such as by blocking the binding of glycosaminoglycans to amyloid fibrils), enhancing clearance of amyloid by immunotherapy, and promoting amyloid regression by targeting SAP.
- SAP is a major component of amyloid deposits of any type.
- Antibodies to human SAP were shown to eliminate visceral AA deposits in mice .
- It is critical not to misdiagnose ALECT2 amyloidosis as AL amyloidosis to avoid harmful therapy.