Why Is This Important?

Amyloid deposits found in biopsy specimens, in combination with identification of a pathogenic variant in TTR, are necessary to establish the diagnosis.¹ Genetic testing is useful for diagnostic confirmation in symptomatic individuals and for testing of at-risk asymptomatic family members (including prenatal diagnosis). Molecular confirmation of a diagnosis may help avoid unnecessary testing and procedures, guide recommendations for medical treatment and screening, and offer accurate genetic counseling (including risk assessment) for a family. 

When To Consider Testing

Genetic testing may be considered for any of the following:

• Confirm a suspected diagnosis of familial TTR amyloidosis and begin treatment
• Differentiate familial TTR amyloidosis from other amyloid disease types
• Offer treatment/screening based on genetic subtype
• Determine carrier status for a known familial mutation

Mutation Detection Rate

Our familial TTR amyloidosis genetic testing can detect >99% of affected individuals (clinical sensitivity) and can detect >99.9% of described sequencing mutations, when present (analytic sensitivity).

Test Description

Our familial TTR amyloidosis genetic testing includes next generation sequencing (NGS) and deletion/duplication analysis of the TTR gene. Genomic deoxyribonucleic acid (gDNA) is isolated from the patient’s specimen using a standardized kit and quantified. Sequence enrichment of the targeted coding exons and adjacent intronic nucleotides is carried out by a bait-capture methodology using long biotinylated oligonucleotide probes, followed by polymerase chain reaction (PCR) and NGS.

Sanger sequencing is performed for any regions missing, or with insufficient read depth coverage for reliable heterozygous variant detection. Reportable small insertions and deletions, potentially homozygous variants, variants in regions complicated by pseudogene interference, and single nucleotide variant calls not satisfying 100x depth of coverage and 40% het ratio thresholds are verified by Sanger sequencing.² This assay targets all coding domains, and well into the flanking 5’ and 3’ ends of all the introns and untranslated regions. Gross deletion/duplication analysis is performed using read-depth from NGS data. Any copy number changes detected by NGS are confirmed by targeted chromosomal microarray or MLPA.

1. Sekijima Y, et al. Familial Transthyretin Amyloidosis. November 5, 2001. In Pagon RA, et al., editors. GeneReviews.® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2016. 
2. Mu W, et al. Sanger confirmation is required to achieve optimal sensitivity and specificity in next-generation sequencing panel testing. J Mol Diagn. 2016. 18(6):923-932.