Assessment of doxycycline treatment on prion deposition in the olfactory epithelium of patients with Fatal Familial Insomnia: Possible mirroring of the CNS alterations

Fatal Familial Insomnia (FFI) is an autosomal dominant inherited prion disease due to a point mutation at position 178 of the prion protein gene (PRNP) resulting in aspartic acid to asparagine substitution (D178N) in coupling phase with methionine at position 129. The overall amount of protease resistant prion protein (PrPres) in FFI is 5-10 times lower than that found in classical forms of sporadic CJD and prevalently affects the thalamus. Recent data showed that prions can be found in the olfactory mucosa (OM) of patients with CJD (Zanusso et al. 2014). The aim of the present study was to verify whether PrPres is also present in the OM of FFI patients and, if this were the case, whether this marker can be used to evaluate the response to pharmacological treatment. First, we optimized the protein misfolding cyclic amplification (PMCA) on samples of frontal cortex from FFI patients. The optimized method allowed to detect a PrPres signal till 10-12-fold dilution of brain homogenate. We then analyzed the OM from a symptomatic FFI patient and found a PrPres signal with a biochemical profile similar to that found in FFI brain. Quantitative PMCA showed that the PrPres concentration in the OM was approximately 1.4 × 10-18 grams/10 microliters. We are currently extending the study to members of a large Italian kindred of FFI involved in a clinical trial aimed to assess the effect of doxycycline (administered at preclinical stage) on disease progression. OM samples, collected at both preclinical and clinical stage of doxycycline-treated and -untreated individuals, will be analyzed to assess whether PrPres can be detected at a pre-symptomatic stage and if the treatment reduces the amount of PrPres or alters its biochemical properties. Since OM belongs to the CNS, the analysis of OM-PrPres might mirror the modifications occurring in the CNS, thus providing important information about the real effect of the doxycycline on prion propagation.