Method Description

Transthyretin:

Transthyretin (TTR) is purified from plasma using online affinity chromatography coupled to a quadrupole time-of-flight mass spectrometer. The acquired ion spectra are deconvoluted and reviewed for TTR variants. After deconvolution, normal patients present with a single peak corresponding to wildtype (wt) TTR, which serves as a reference. When positive, amyloid patients are typically heterozygous and are detected by the presence of 2 peaks (ie, wt TTR and altered TTR) differing in mass.(Bergen HR 3rd, Zeldenrust SR, Butz ML, et al. Identification of transthyretin variants by sequential proteomic and genomic analysis. Clin Chem. 2004;50[9]:1544-1552; Trenchevska O, Yassine HN, Borges CR, et al. Development of quantitative mass spectrometric immunoassay for serum amyloid A. Biomarkers. 2016;21[8]:743-751)

TTR Gene Sequencing:

Next generation sequencing (NGS) and/or Sanger sequencing are performed to test for the presence of variants in coding regions and intron/exon boundaries of TTR, as well as some other regions that have known disease-causing variants. The human genome reference GRCh37/hg19 build was used for sequence read alignment. At least 99% of the bases are covered at a read depth over 30X. Sensitivity is estimated at above 99% for single nucleotide variants, above 94% for deletion-insertions (delins) less than 40 base pairs (bp), above 95% for deletions up to 75 bp and insertions up to 47 bp. NGS and/or a polymerase chain reaction-based quantitative method is performed to test for the presence of deletions and duplications in TTR

There may be regions of TTR that cannot be effectively evaluated by sequencing or deletion and duplication analysis as a result of technical limitations of the assay, including regions of homology, high guanine-cytosine (GC) content, and repetitive sequences.(Unpublished Mayo method)

The reference transcript for TTR gene is NM_000371.3. Reference transcript numbers may be updated due to transcript re-versioning. Always refer to the final patient report for gene transcript information referenced at the time of testing.