Type I familial amyloidotic polyneuropathy in Japan.

We studied 107 cases and 64 carriers of type I familial amyloidotic polyneuropathy (FAP) residing in 16 districts in Japan. The age of onset of illness ranged from 20 to 71 years old, with a mean of 40.1 +/- 12.8 years (SD). One quarter of the cases were late-onset patients who developed the disorder after age 50. Asymptomatic carriers older than age 50 accounted for 20% of total carriers, with the oldest carrier being a 94-year-old woman. All the patients had a variant transthyretin with a methionine-for-valine substitution at position 30 with a mean serum level of 9.78 +/- 3.27 (SD) mg/dl. The serum level did not significantly differ by gender in either patients or carriers, nor between patients and carriers. Incomplete penetrance of clinical expression was shown in eight cases. This study indicates that there is a considerable variety in age of onset, progression and geographic distribution of type I FAP in Japan.