Pathology of early- vs late-onset TTR Met30 familial amyloid polyneuropathy

Background: Late-onset type I familial amyloid polyneuropathy (FAP TTR Met30) cases unrelated to endemic foci in Japan show clinical features setting them apart from early-onset cases in endemic foci. Objective: To compare pathologic features between the early- and late-onset types. Methods: Pathologic findings in FAP TTR Met30 with onset before age 50 in relation to endemic foci (11 cases) were compared with those in 11 later-onset cases unrelated to endemic foci. Results: Sural nerve biopsy specimens showed predominantly small-fiber loss in early-onset cases; variable fiber size distribution, axonal sprouting, and relatively preserved unmyelinated fibers characterized late-onset cases. Autopsy cases representing both groups showed amyloid deposition throughout the length of nerves and in sympathetic and sensory ganglia, but amounts were greater in early- onset cases. Amyloid deposition and neuronal cell loss were greater in sympathetic than dorsal root ganglia in early-onset cases; the opposite was true in late-onset cases. Size assessment of remaining neurons in these ganglia suggested predominant loss of small neurons in early-onset cases but loss of neurons of all sizes in late-onset cases. Transthyretin-positive, Congo red-negative amorphous material was more conspicuous in nerves from late- than early-onset cases. In extraneural sites, amyloid was more conspicuous in thyroid and kidney from early-onset cases and in heart and hypophysis from late- onset cases. In early-onset cases, cardiac amyloid deposition was prominent in the atrium and subendocardium but was conspicuous throughout the myocardium in late- onset cases. Conclusion: The pathology of early- and late-onset FAP TTR Met30 correlated well with differences in clinical findings.