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Test ID: TTRX Amyloidosis, Transthyretin-Associated Familial, Reflex, Blood

Reporting Name

Familial Amyloidosis Reflex

Useful For

Diagnosis of adult individuals suspected of having transthyretin-associated familial amyloidosis

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
ATTRZ TTR Gene, Full Gene Analysis Yes No

Testing Algorithm

If familial amyloidosis by liquid chromatography-mass spectrometry is abnormal, DNA sequence will be performed and charged separately.

 

See Amyloidosis (Familial) Test Algorithm in Special Instructions.

Specimen Type

Whole blood


Shipping Instructions


Specimen must arrive within 96 hours of draw.



Specimen Required


Container/Tube:

Preferred: Lavender top (EDTA)

Acceptable: ACD

Specimen Volume: 3 mL

Collection Instructions:

1. Invert several times to mix blood.

2. Send specimen in original tube.


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Whole blood Refrigerated (preferred) 4 days
  Ambient  4 days

Reference Values

An interpretive report will be provided.

Day(s) and Time(s) Performed

Tuesday; 8 a.m.

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

82542 LC-MS

81404 TTR gene (if appropriate)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
TTRX Familial Amyloidosis Reflex In Process

 

Result ID Test Result Name Result LOINC Value
22668 Wild Type Mass In Process
22669 Wild Type Width at Half Height In Process
22670 Second Mass In Process
22671 Mass Difference In Process
22673 Abnormal result In Process
50944 Interpretation 59462-2
50946 Reviewed By No LOINC Needed

Clinical Information

The systemic amyloidoses are a group of diseases that result from the abnormal deposition of amyloid in various tissues of the body. They have been classified into 3 major types: primary, secondary, and hereditary. The most common form of amyloidosis (AL) is a disease of the bone marrow called primary systemic AL (immunoglobulin light chain). Secondary AL usually occurs in tandem with chronic infectious or inflammatory diseases, such as rheumatoid arthritis, tuberculosis, or osteomyelitis. Familial or hereditary AL is the least common form. Determining the specific type of AL is imperative in order to provide both an accurate prognosis and appropriate therapies.

 

Familial or hereditary transthyretin AL is an autosomal dominant disorder caused by mutations in the transthyretin gene (TTR). The resulting amino acid substitutions lead to a relatively unstable, amyloidogenic transthyretin (TTR) protein. Most individuals begin to exhibit clinical symptoms between the third and seventh decades of life. Affected individuals may present with a variety of symptoms including sensorimotor and autonomic neuropathy, vitreous opacities, cardiomyopathy, nephropathy, and gastrointestinal dysfunction. TTR-associated AL is progressive over a course of 5 to 15 years and usually ends in death from cardiac or renal failure or malnutrition. Orthotopic liver transplantation is a treatment option for some patients who are diagnosed in early stages of the disease.

 

Mayo Medical Laboratories recommends a testing strategy that includes both protein analysis by mass spectrometry (MS) and TTR gene analysis by DNA sequencing (ATTRZ / TTR Gene, Full Gene Analysis) for patients in whom TTR-associated familial AL is suspected. The structure of TTR protein in plasma is first determined by MS. The presence of a pathogenic variant in the TTR gene leads to conformational changes in the TTR protein. This ultimately disrupts the stability of the mature TTR protein tetramer, leading to increased amounts of pro-amyloidogenic TTR monomers in the plasma of affected individuals. MS is able to identify mass difference between wild type TTR and variant TTR protein. Only the transthyretin (also known as prealbumin) is analyzed for amino acid substitutions. Other proteins involved in other less common forms of familial amyloidosis are not examined. If no alterations are detected, gene analysis will not be performed unless requested by the provider (ie, when the diagnosis is still strongly suspected; to rule out the possibility of a false-negative by MS). In all cases demonstrating a structural change by MS, the entire TTR gene will be analyzed by DNA sequence analysis to identify and characterize the observed alteration (gene mutation or benign polymorphism). More than 90 mutations that cause TTR-associated familial AL have now been identified within the TTR gene. Most of the mutations described to date are single base pair changes that result in an amino acid substitution. Some of these mutations correlate with the clinical presentation of AL.

 

For predictive testing in cases where a familial mutation is known, testing for the specific mutation by DNA sequence analysis (FMTT / Familial Mutation, Targeted Testing) is recommended. These assays do not detect mutations associated with non-TTR forms of familial AL. Therefore, it is important to first test an affected family member to determine if TTR is involved and to document a specific mutation in the family before testing at risk individuals.

Interpretation

The presence of a structural change in transthyretin (TTR) is suggestive of a gene mutation that requires confirmation by DNA sequence analysis. A negative result by mass spectrometry does not rule out a TTR mutation. Mass spectrometric (MS) results are falsely negative if the amino acid substitution does not produce a measurable mass shift for the mutation transthyretin. Approximately 90% of the TTR mutations are positive by MS (see Cautions).

 

After identification of the mutation at the DNA level, predictive testing for at-risk family members can be performed by molecular analysis (FMTT / Familial Mutation, Targeted Testing).

Clinical Reference

1. Shimizu A, Nakanishi T, Kishikawa M, et al: Detection and identification of protein variants and adducts in blood and tissues: an application of soft ionization mass spectrometry to clinical diagnosis. J Chromatogr B Analyt Technol Biomed Life Sci 2002 Aug 25;776(1):15-30

2. Lim A, Prokaeva T, McComb ME, et al: Characterization of transthyretin variants in familial transthyretin amyloidosis by mass spectrometric peptide mapping and DNA sequence analysis. Anal Chem 2002 Feb 15;74(4):741-751

3. Sekjima Y, Yoshida K, Tokuda T, Ikeda S: Familial Transthyretin Amyloidosis In GeneReviews. Edited by RA Pagon, MP Adam, HH Ardinger, et al: Retrieved February 6, 2017.Available at https://www.ncbi.nlm.nih.gov/books/NBK1194/

4. Theberge R, Connors LH, Skinner M, Costello CE: Detection of transthyretin variants using immunoprecipitation and matrixassisted laser desorption/ionization bioreactive probes: a clinical application of mass spectrometry. J Am Soc Mass Spectrom. 2000,11:172-175

Analytic Time

7 days (Not reported Saturday or Sunday)

Method Name

Liquid Chromatography-Mass Spectrometry (LC-MS)

Forms

1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.

2. If not ordering electronically, complete, print, and send 1 of the following forms with the specimen:

Neurology Specialty Testing Client Test Request (T732) (http://www.mayomedicallaboratories.com/it-mmfiles/neurology-request-form.pdf)

Hematopathology/Cytogenetics Test Request Form (T726) with the specimen (http://www.mayomedicallaboratories.com/it-mmfiles/hematopathology-request-form.pdf)

Mayo Medical Laboratories | Genetics and Pharmacogenomics Catalog Additional Information:

mml-biochemical