knowledge of the VDE can then usefully implement our di-agnostic (prognostic) armamentarium of these tumors.

Several clarifications are required. First, the patients were“excluded” for the measurement of VDE, estimated before on-cological treatment or anaplastic transformation, in the in-tent of correlating a “grade 2 velocity” to its further biolog-ical behavior.2 Second, our initial statistical analysis was doneat time zero (for tumor volume and follow-up), correspond-ing to the date of histological diagnosis (hence without anytime-dependent covariable). For the purpose of our articleand its practical consequences, the presented data considerthe overall follow-up beginning at the time of the first MRIavailable.2 No cases were excluded that fulfilled the inclusioncriteria. Third, the reason of a random review, conductedblindly, was to ensure the probability that none of thesecases, whatever the group for VDE, would be reclassified as ahigher grade. The purpose of our article was precisely, in theconditions of daily practice, to suggest that analyzing VDEcould be a way to overcome our current limits, of histolog-ical diagnosis among others.2 Until now, we have indeedfailed to find discriminant histological criteria to reliably dif-ferentiate G2G of different VDE.

Department of Neurosurgery, Pitie-Salpetriere Hospital, Paris,France

References1. Mandonnet E, Delattre JY, Tanguy ML, et al. Continuous

growth of mean tumor diameter in a subset of grade II gliomas.Ann Neurol 2003;53:524–528.

2. Pallud J, Mandonnet E, Duffau H, et al. Prognostic value ofinitial magnetic resonance imaging growth rates for WorldHealth Organization grade II gliomas. Ann Neurol 2006;60:380–383.

DOI: 10.1002/ana.21132

Proteomic Discovery of CSF Biomarkers forAlzheimer’s DiseaseJing Zhang, MD, PhDand Thomas J. Montine, MD, PhD

We read with great interest Finehout and colleagues’ recentarticle entitled “Cerebrospinal Fluid Proteomic Biomarkersfor Alzheimer’s Disease.”1 We congratulate Dr Finehout andher colleagues on an important contribution to the search forbiomarkers of Alzheimer’s disease. Nonetheless, we notesome shortcomings that we suspect will limit the ultimateutility of these results: (1) there were only nine control sub-jects, and likely because of this low number there was noaccounting for age-related changes in any of the proposedbiomarkers; (2) there was a larger number of individuals withneurological diseases other than Alzheimer’s disease that wereused as a reference group, but only three patients with otherforms of dementia, thereby precluding assessment of speci-ficity; and (3) there was no objective control for contamina-tion of cerebrospinal fluid by blood, a potentially seriousconfounder when the list of candidates contains several pro-teins that are abundant in plasma. Finally, the authors ne-glected to note that each of their candidates already had beenreported in other proteomic studies of cerebrospinal fluid

from patients with Alzheimer’s disease, and that there areimportant quantitative differences across these studies2 andseveral older studies previously reviewed.3 For this area ofinvestigation to move forward expeditiously, we think it iscritically important that cerebrospinal fluid biomarker studiesinclude analysis of age-related changes in healthy volunteers,clinically relevant estimates of specificity and not simply as-sociation with demented stage of Alzheimer’s disease, objec-tive control for blood contamination of cerebrospinal fluid,and comparison of results across studies, especially whensample numbers are low.

Department of Pathology, University of Washington, Seattle,WA

References1. Finehout EJ, Franck Z, Choe LH, et al. Cerebrospinal fluid pro-

teomic biomarkers for Alzheimer’s disease. Ann Neurol 2007;61:120–129.

2. Abdi F, Quinn JF, Jankovic J, et al. Detection of biomarkerswith a multiplex quantitative proteomic platform in cerebrospi-nal fluid of patients with neurodegenerative disorders. J Alzhei-mers Dis 2006;9:293–348.

3. Montine TJ, Woltjer RL, Pan C, et al. Liquid chromatographywith tandem mass spectrometry-based proteomic discovery in ag-ing and Alzheimer’s disease. NeuroRx 2006;3:336–343.

Reply: Cerebrospinal Fluid Proteomics forBiomarkers of Alzheimer’s DiseaseKelvin H. Lee1 and Norman R. Relkin2

We appreciate the opportunity to respond to commentsmade by Drs Zhang and Montine regarding our recent pub-lication in Annals of Neurology1 and would like to clarify afew points. First, we presented data on 34 non–Alzheimer’sdisease (AD) control subjects in the test study, of which 9were considered to be healthy control subjects with the oth-ers as neurologic control subjects. The validation cohort had18 non-AD control subjects, of which 3 were healthy controlsubjects. Second, we highlight that the validation cohort ofsubjects included eight demented subjects. Third, we wereunable to use an apolipoprotein B plasma/cerebrospinal fluid(CSF) ratio to monitor for blood contamination becauseplasma samples were unavailable for most subjects. Althoughthis measure, used in Abdi and colleagues’2 study, is an ex-cellent objective measure, we could not apply it because mostof the samples were shared from various tissue banks that didnot have corresponding plasma samples. Instead, we assessedpossible blood contamination by the presence of markerspots (peroxiredoxin, catalase, carbonic anhydrase I, and he-moglobin) that are indicative of blood contamination of CSFby two-dimensional gel electrophoresis.3

We agree with the comment that it is important to studyage-related changes in healthy volunteers. The eventual clin-ical application of CSF biomarkers will require identificationand characterization of any significant covariables, and agecould prove to be one of these. However, it is also conceiv-able that some markers will be relatively age independent. Inan ideal world, one examines other variables as well (eg, sex,race, genetics, duration of dementia, among others); how-ever, the reality is that CSF from autopsy-proven cases is

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