Transthyretin (TTR) familial amyloid polyneuropathies (FAP) are autosomal dominant devastating afflictions. They were first described in Portugal, later in Japan and Sweden and are now recognized worldwide. The TTR Val30Met mutation is the most common, and depending on the geographic origin, a wide variation in age at onset of the disease is observed. In Europe, northern Sweden is the second most prevalent area of the disease, and a late age of onset of 56 years has been reported. The present study aims to estimate the penetrance in TTR Val30Met Swedish families. Genealogical investigations, clinical data and genotyping were obtained in 77 TTR-Val30Met Swedish families. The penetrance in Val30Met carriers and variation within the endemic area, according to gender and transmitting parents were calculated by a newly developed bias-free method. The penetrance estimates were low, i.e. 1.7% and 22% at age 30 and 60 years, respectively, and far from complete (69%) by age 90 years. Differences between Piteå and Skellefteå regions were observed. Moreover, penetrance was significantly higher when the mutation was inherited from the mother than from the father. The low penetrance observed in TTR FAP kindreds and its variations is important information for the genetic counseling and treatment of Swedish FAP patients and their families.
Background
The amyloid fibril in hereditary transthyretin (TTR) Val30Met (pVal50Met) amyloid (ATTR Val30Met) amyloidosis is composed of either a mixture of full-length and TTR fragments (Type A) or of only full-length TTR (Type B). The type of amyloid fibril exerts an impact on the phenotype of the disease, and on the outcome of diagnostic procedures and therapy. The aim of the present study was to investigate if the type of amyloid fibril remains the same within ATTR Val30Met amyloidosis families.
Methods
Fifteen families were identified in whom at least two first-degree relatives had their amyloid fibril composition determined. The type of ATTR was determined by Western blot in all but two patients. For these two patients a positive 99mTc-3,3-diphosphono-1,2-propanodicarboxylic acid scintigraphy indicated ATTR Type A.
Results
In 14 of the 15 families, the same amyloid fibril composition was noted irrespective of differences in age at onset. In the one family, different ATTR fibril types was found in two brothers with similar ages at onset.
Conclusions
Family predisposition appears to have an impact on amyloid fibril composition in members of the family irrespective of their age at onset of disease, but if genetically determined, the gene/genes are likely to be situated at another location than the TTR gene in the genome.
View related articlesView Crossmark data Citing articles: 4 View citing articles TTR: transthyretin; BMI: body mass index; BNP: brain natriuretic peptide; AST: aspartate aminotransferase; ALT: alanine aminotransferase. Data shown are medians (full range). p Values <.05 were considered statistically significant.
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