Late-onset familial amyloid polyneuropathy in Japan.

Transthyretin (TTR) Val30Met-associated familial amyloid polyneuropathy (FAP ATTR Val30Met) is the most common form of FAP. We compared the clinicopathological features and natural history of late-onset FAP ATTR Val30Met cases from non-endemic areas of Japan with early-onset cases from endemic foci. The characteristics of early-onset cases from endemic foci of Japan included the presence of sensory dissociation and marked autonomic dysfunction associated with a predominant loss of small-diameter myelinated and unmyelinated nerve fibers. These characteristics were not common in the late-onset cases from non-endemic areas. The distribution and characteristics of amyloid deposits in late-onset cases were similar to those of senile systemic amyloidosis with wild-type TTR deposition. The causal mechanism of differences between the early- and late-onset forms of FAP with the same mutation in the TTR gene has not yet been determined.