A 61-year-old Japanese woman with transthyretin amyloid (ATTR) Tyr69Ile, which was caused by the mutation of TTR gene TAC to ATC at codon 69, is described. The patient had no family history and developed carpal tunnel syndrome followed by congestive heart failure due to cardiac amyloidosis. Various phenotypes of familial transthyretin amyloidosis including FAP are caused by TTR variants with single amino-acid substitutions, the latter being caused by one-point mutations in the coding region of the TTR gene. This is the first report showing a novel double-nucleotide substitution in the causative TTR gene abnormality.