1. Baxter Laboratory for Stem Cell Biology, Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA.
2. Center for Genetic Disorders and Aging, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, CA 92037, USA.
3. Vincent Coates Foundation Mass Spectrometry Laboratory, Stanford University, Stanford, CA 94305, USA.
4. Department of Pathology, Stanford University, Stanford, CA 94305, USA.
5. Department of Neuropathology, Stanford University, Stanford, CA 94305, USA.