14Neuroimaging Initiative (ADNI) database (adni.loni.usc.edu). As such, the investigators 15 within the ADNI contributed to the design and implementation of ADNI and/or provided data 16 but did not participate in analysis or writing of this report. A complete listing of ADNI 17 investigators can be found at:18 Abstract 50 Sensitive and accurate biomarkers for the prediction of conversion from mild cognitive 51 impairment (MCI) to Alzheimer's Disease (AD) are needed to both support clinical care and 52 enhance clinical trial design. Here, we examined the potential of cerebrospinal fluid (CSF) levels 53 of a peptide derived from a neural protein involved in synaptic transmission, VGF (a non-54 initialism), to enhance accuracy of prediction of conversion from MCI to AD. The performance 55 of conventional biomarkers (CSF Aβ1-42 and phosphorylated tau +/-hippocampal volume) was 56 compared to the same biomarkers with CSF VGF peptide levels. It was observed that VGF 57 peptides are lowered in patients with AD compared to controls and that combinations of CSF 58 Aβ1-42 and phosphorylated tau, hippocampal volume and VGF peptide levels outperformed 59 conventional biomarkers alone (hazard ratio = 2.2 vs. 3.9). VGF peptide levels were correlated 60 most strongly with total tau levels, but not hippocampal volume, suggesting that they serve as a 61 3 marker for neuronal degradation, but not necessarily in the hippocampus. The latter point 62 suggests that VGF may serve as a more general marker of neurodegeneration. Future work will 63 be needed to determine the specificity of VGF for AD vs. other neurodegenerative diseases. 64 Introduction 65 Alzheimer Disease (AD) is characterized by a long prodromal course during which a number of 66 pathological changes occur prior to the onset of clinical symptoms. Classically, these changes 67 include the deposition of amyloid beta (Aβ) and phosphorylated tau (pTau) into the brain, 68 hippocampal atrophy and disruptions of metabolism, particularly in the temporal and parietal 69 cortices (for review of preclinical pathology and biomarkers, please see [1]). It is speculated that 70 these biomarkers are part of a cascade whereby Aβ triggers a series of pathological events, 71 leading to neuronal dysfunction, hyperphosphorylation of tau and consequent synaptic loss, 72 leading to volume loss and metabolic disruption [2-4]. These changes have formed the basis for 73 the use of a series of fluid and imaging biomarkers to facilitate clinical and research practice.74 75 AD biomarkers may be used to 1) achieve earlier diagnoses for patients, 2) predict which 76 individuals are most likely to clinically worsen over time, 3) help to identify and stratify subjects 77 enrolling in AD-related clinical trials and 4) serve as outcome measurements in AD-related 78 clinical trials [5-7]. For example, there is a 10-15% misdiagnosis rate when AD is diagnosed on 79 clinical grounds only. This high rate of misdiagnosis has substantial cost implications [8-11] and 80 if such misdiagnosed subjects are enrolle...