Consistent with the pediatric nature of Glut1 DS and reminiscent of the outcome of similar studies (37, 38) on another infantile-onset disease, spinal muscular atrophy, the earlier we effected Glut1 haploinsufficiency in our conditional mutants, the more closely we were able to mimic disease in constitutively haploinsufficient mutants and in human patients. The gene discussed is SLC2A1; the disease is proximal spinal muscular atrophy.