Beyond Val30Met transthyretin (TTR): variants associated with age-at-onset in hereditary ATTRv amyloidosis

Abstract

Objectives

V30M in transthyretin (TTR) gene is causative for hereditary ATTRv amyloidosis (familial amyloid polyneuropathy). ATTRv amyloidosis shows a wide variation in age-at-onset (AO) between clusters, families, and among generations. We aim at identifying genetic modifiers of disease onset that may contribute to this variability in Portuguese patients by identifying other variants in TTR locus, beyond the ATTRv amyloidosis causing variant that could play a regulatory role in its expression level.

Methods

We analysed DNA samples of 330 ATTRV30M carriers (299 patients, 31 aged-asymptomatic carriers aged >40 years) from 120 families currently under follow-up. A generalised estimating equation analysis (GEE) was used to take into account non-independency of AO between relatives. An intensive in silico analysis was performed in order to understand a possible regulation of gene expression.

Results

We found 11 rare variants in the promoter, coding and intron/exon boundaries of the TTR gene associated with the onset of symptoms before and after age 40 years, namely 2 novel ones and a tandem CA-dinucleotide repeat. Furthermore, of the 4 common variants found, one was significantly associated with AO and may influence the constitutive splicing of TTR pre-mRNA. The seven ATTRV30M/V30M homozygous do not carry any of the variants identified in this study, including the common ones. In silico analysis disclosed significant alterations in the mechanism of splicing, transcription factors and miRNAs binding.

Conclusions

Variants within the promoter region may modify disease expressivity and variants in the 3’UTR can impact the efficacy of novel therapeutic interventions. Importantly, the putative mechanisms of regulation of gene expression within the TTR gene deserve to be better explored, in order to be used in the future as potential therapeutical targets.

Keywords:

• Age-at-onset
• familial amyloid polyneuropathy
• TTR gene
• promoter
• hereditary transthyretin
• genetic modifiers

Acknowledgments

We thank all the patients and families for participating in this study and Joana Silva for all the help with the optimization of protocol for sequencing.

Disclosure statement

T.C.’s institution has received support from FoldRx Pharmaceuticals, which was acquired by Pfizer Inc in October 2010; T.C. has served on the scientific advisory board of Pfizer Inc and received funding from Pfizer Inc for scientific meeting expenses (travel, accommodations, and registration). T.C. currently serves on the THAOS (natural history disease registry) scientific advisory board.

The other authors have no conflicts of interest.

Additional information

Funding

We would like to thank FEDER funds, through the Programa Operacional Factores de Competitividade – COMPETE 2020 and by Nacional funds through the FCT – Fundação para a Ciência e a Tecnologia [COMPETE: POCI-01-0145-FEDER-007440]. This work was supported by grants of Fundação para a Ciência e Tecnologia, FCT [PTDC/SAU-GMG/100240/2008 and PEsT], co-funded by ERDF and COMPETE; and by Financiamento Plurianual de Unidades de Investigação (FCT). MAF is recipient of a FCT fellowship [SFRH/BD/101352/2014]. The funders had no role in the design and conduct of the study; collection, management, analysis, or interpretation of the data; preparation, review, or approval of the manuscript; or decision to submit the manuscript for publication.