Ineffectiveness of dialysis in transthyretin (TTR) clearance in Familial Amyloid Polyneuropathy type I, in spite of lower stability of the TTR Met30 variant

Background: Familial Amyloid Polyneuropathy (FAP) is an hereditary form of systemic amyloidosis related to a mutant transthyretin (TTR). The renal disease ranges from proteinuria to end-stage renal failure (ESRF), with replacement of renal function by dialysis. In comparison with FAP patients with normal renal function, the progression of the neurologic disease seems to be retarded in FAP patients on dialysis. Patients and methods: We evaluated the influence of hemodialysis and hemodiafiltration on plasma TTR levels in 6 FAP patients with ESRF, which were on regular hemodialysis for 4 months to 6 years, prior to this study. Hemodialysis performed was over a two-week period, one week with a cellulose triacetate membrane and the other with a polysulfone membrane. In the third week, patients were submitted to hemodiafiltration. Plasma TTR levels were measured at the beginning, 60 min, 120 min, and at the end of each session. We also evaluated the TTR adsorbed by the membrane and in the dialysate. Results: TTR levels did not change significantly with the dialysis. The total amount of TTR adsorbed to the membrane was always < 2 mg and found in the dialysate < 1 mg. Hemodialysis and hemodiafiltration were ineffective in removing TTR, in spite of lower stability of the TTR Met30 variant. Conclusion: The protective feature of hemodialysis on the progression of the amyloidosis is not due to the clearance of this abnormal protein from plasma.