Reply to Roerink et al.: Metabolomics of chronic fatigue syndrome, by Robert K. Naviaux and Eric Gordon in PNAS 2017 114 (6) E911-E912; [published ahead of print January 26, 2017]
We thank Roerink et al. (1) for their comments. We respond to their two points in order.
Their first point asked about the effect of physical activity on sphingolipids. The phingolipid response to exercise is complex. It differs in healthy trained and untrained individuals and has not yet been studied using methods that can distinguish the classes of sphingosines, ceramides, sphingomyelins, and glycosphingolipids measured
in our analysis of myalgic encephalomyelitis (ME)/chronic fatigue syndrome (CFS) (2)…
Second, Roerink et al. (1) raise questions about the standard statistical methods used in metabolomics studies. We used multivariate analysis by partial least squares discriminate analysis (PLSDA), area under the receiver operator characteristic (AUROC) curve analysis,
random forest methods for biomarker discovery, repeated double cross-validation, and permutation analysis…
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