Abstract: Familial amyloidotic polyneuropathy (FAP) is a lethal genetic disorder that affects the peripheral and autonomic nervous systems, heart, gastro-intestinal (GI) tract, and soft tissues. Disease progression is increasingly reported following liver transplantation, the only proven treatment for FAP. Small molecule thyroxine mimetics stabilize transthyretin, inhibiting FAP amyloid fibril formation under stringent in vitro conditions. We report on the progress of an international, randomized placebo-controlled study designed to determine the effect of diflunisal, a thyroxine mimetic, on neurologic disease progression in patients with active FAP. Our experience to date indicates diflunisal is well tolerated by this study cohort and that neurologic disease advances more rapidly in FAP than it does in diabetes mellitus.
Background: Transthyretin-related familial amyloidotic polyneuropathy (FAP) is a lethal autosomal dominant genetic disorder that predominantly affects the peripheral nervous system. FAP amyloid fibrils result from the misfolding of transthyretin, a transport protein predominantly produced by the liver. Although liver transplantation effectively treats patients with certain FAP mutations and limited disease, reports increasingly document progressive amyloid deposition following transplantation [1,2]. Alternative treatments are needed. In vitro investigations and a phase I clinical trial have demonstrated that thyroxine and small molecule mimetics, e.g. diflunisal, inhibit tetrameric transthyretin dissociation and suppress amyloid fibril formation [3,4].
Methods: To examine the effect of diflunisal on disease progression in FAP, we designed a randomized, placebo controlled, double blind, multicenter international study employing the validated diabetic (DM) polyneuropathy metric, Neurologic Impairment Score + 7 attributes (NIS+7®), as the primary endpoint. A two-point change in NIS+7 correlates with clinically detectable progression of peripheral neuropathy among diabetics . Entry criteria include proven FAP genotype, biopsy-proven amyloid deposits, and peripheral or autonomic neuropathy. Patients with alternate causes of neuropathy, other NSAID use, severe heart or kidney dysfunction, or previous liver transplantion are excluded. Study evaluations occur at entry, 6, 12, and 24 months. Adverse are collected by monthly telephone interviews, diary entries, and study site visit interactions. Relatedness of adverse events to study drug is assigned according to documentation in the investigational brochure, the protocol, the informed consent form; or at the investigator's discretion.
Results: To date, 90 subjects have enrolled – 62 men and 28 women with median age 63 years (range 27–76 years). Adverse events tabulated by affected organ systems predominantly involved gastrointestinal events, more often attributed to disease complications than study drug side effects (Table 1). Although rare events, congestive heart failure in two subjects and GI bleeding in another prompted study drug discontinuation. Two disease-related deaths have occurred, both off study drug. Aggregate data from all study subjects (placebo and active drug arms) followed for at least 12 months identified a 3.2 point increase in median NIS+7 summated scores. In contrast, Dyck et al.  reported an annual 0.85 point increase in NIS+7 median scores in a large cohort of diabetics with polyneuropathy. Taken together, NIS+7 detected neurologic disease progression in this FAP cohort after 12 months observation. Additionally, NIS+7 measured disease advanced 3.5 times faster in our aggregate FAP study population than previously reported in DM.
Conclusions: Diflunisal is well tolerated in FAP patients participating in the study. NIS+7, a composite scoring system, appears to be an effective study instrument for ATTR neuropathy, detecting significant change over 12 months observation. Neurologic disease progresses more rapidly in FAP than DM cohorts. The exact rate of disease progression in untreated FAP subjects detected by NIS+7 awaits unblinding of the data. These data will provide basis for future study design in FAP patients.
2011. Vol. 18, no Suppl. 1, 191-192 p.