1. Department of Ophthalmology, Children's Hospital Boston, 2Department of Neurobiology, Harvard Medical School, Boston, MA 02215, USA, 3Queensland Centre for Medical Genomics, Institute for Molecular Bioscience, The University of Queensland, St. Lucia 4072, Australia, 4Epicentre (an Illumina Company), 726 Post Rd., Madison, WI 53713, USA and 5Swartz Center for Theoretical Neuroscience, Harvard University, Cambridge, MA 02138, USA