Systems Biology Group, Biostatistics Branch, National Institute of Environmental Health Sciences, National Institute of Health, Research Triangle Park, NC 27709, USA, School of Mathematics and Statistics, University of Sydney, Diabetes and Obesity Program, Garvan Institute of Medical Research, NSW 2006, Australia and Metabolism in Human Disease Unit, Institute of Molecular and Cellular Biology, A*Star, 61 Biopolis Drive, Proteos 138673, Singapore.