Development of an automated capillary nano-immunoassay-Simple Western assay-to quantify total TDP43 protein in human platelet samples.

Frontotemporal lobar degeneration syndrome is the second cause of young-onset dementia. Unfortunately, reliable biomarkers are currently lacking for the diagnosis of this disease. As TDP43 protein is one of the proteins pathologically involved in frontotemporal lobar degeneration, many studies have been performed to assess TDP43 protein diagnostic performances. Mixed results were obtained using cerebrospinal fluid and plasma samples so far. The aim of the study was to develop an automated capillary nano-immunoassay-Simple Western assay-to detect and quantify TDP43 protein simultaneously in human blood-based samples. Simple Western assay was developed with two different cell lysates used as positive controls and was compared to Western blot. TDP43 protein profiles in plasma samples were disappointing, as they were discordant to our positive controls. On the contrary, similar TDP43 patterns were obtained between platelet samples and cell lysates using both assays. Simple Western assay provided good quantitative performances in platelet samples: a linearity of signals could be observed (r2 = 0.994), associated to a within-run variability at 5.7%. Preliminary results based on a cohort of patients suffering from frontotemporal lobar degeneration showed large inter-individual variations superior to Simple Western's analytical variability. Simple Western assay seems to be suitable for detecting and quantifying TDP43 protein in platelet samples, providing a potential candidate biomarker in this disease. Further confirmation studies should now be performed on larger cohorts of patients to assess diagnostic performances of TDP43 protein in platelet samples.

Association of cerebrospinal fluid prion protein levels and the distinction between Alzheimer disease and Creutzfeldt-Jakob disease.

IMPORTANCE: Although typical forms of Alzheimer disease (AD) and Creutzfeldt-Jakob disease (CJD) are clinically distinguishable, atypical AD phenotypes may pose a diagnostic challenge. The major biological diagnostic biomarker for identifying CJD, 14-3-3 protein in cerebrospinal fluid (CSF), unfortunately lacks specificity when confronting a rapid dementia presentation. OBJECTIVE: To assess the relevance of total CSF prion protein (t-PrP) levels in the differential biological diagnosis between atypical AD phenotypes and CJD. DESIGN, SETTING, AND PARTICIPANTS: A retrospective study in an autopsy-confirmed cohort of 82 patients was performed to evaluate the relevance of CSF t-PrP to distinguish 30 definite cases of AD from 52 definite cases of CJD. Next, CSF t-PrP concentration was measured in a cohort of 104 patients including 55 patients with probable AD, 26 with probable sporadic CJD, and 23 control patients for whom 14-3-3 protein, total tau, phosphorylated tau 181 (P-tau181), and Aß1-42 were available. We investigated 46 patients diagnosed as having probable AD who presented atypical phenotypes. A diagnosis strategy was proposed to classify atypical AD phenotypes with suspicion of CJD based on a decision tree combining CSF biomarkers. MAIN OUTCOMES AND MEASURES: We determined CSF t-PrP levels for all patients. We calculated the ratio of total tau and P-tau181 and determined the diagnostic accuracy of each biomarker alone or in combination. We calculated the misclassification rate for each biomarker that corresponded to the percentage of patients within the group of atypical AD phenotypes wrongly classified as CJD. RESULTS: In patients with CJD, CSF t-PrP concentrations were decreased compared with control participants and patients with AD. When considering the differential diagnosis of CJD compared with atypical AD phenotypes, CSF t-PrP determination reached 82.1% sensitivity and 91.3% specificity. The misclassification rate of atypical AD phenotypes decreased from 43.5%, obtained when using the CSF 14-3-3 protein determination alone, to only 4.3% when calculating the ratio total tau/(P-tau181 × t-PrP). The proposed classification tree permitted correct classification of 98.4% of the patients. CONCLUSIONS AND RELEVANCE: For unusual phenotypes of AD, especially cases presenting with a biological ambiguity suggesting CJD, determination of CSF t-PrP levels increased diagnostic accuracy. The use of CSF t-PrP levels may be beneficial in clinical practice in addition to the current classic biomarkers.