**9. Acknowledgment**

This work was supported by grants to C.J.H. from the National Institutes of Health-National Institute of Neurological Disorders and Stroke (NS034382 and NS051462). S.M.E. was supported by the Tim E. Noel fellowship from the ALS Society of Canada and the Canadian Institutes of Health Research (CIHR). K.A.Q. was supported by the NRSA F32 fellowship (NS063535). T.L.E. was supported by the Joseph A. Blazek Foundation.
