Boston Children’s Hospital is developing the infrastructure needed for large-scale psychiatric research and treatment discovery. The Manton Center for Orphan Disease Research and the BCH Developmental Neuropsychiatry Program seek to develop therapeutics to prevent the development of schizophrenia in at-risk children. Precision Medicine is employed by identifying causative mutations in the youngest patients presenting with psychosis, creating neuronal cell cultures and models of neural networks expressing the mutations and using these to screen for novel therapeutics. The study of rare Mendelian forms of Juvenile Psychosis is an effective way to discover new candidate genes for the condition. As an example of the progress being made, we describe several case studies, including a patient with onset of command auditory hallucinations and behavioral regression at age 6 in the context of longer standing selective mutism, aggression, and mild motor delays. Sequencing revealed a previously unreported heterozygous de novo mutation at c.385G>A in ATP1A3. This gene codes for a neuron-specific isoform of the catalytic alpha subunit of the ATP-dependent transmembrane sodium-potassium pump. Heterozygous mutations in this gene have been reported as causing both sporadic and inherited forms of Alternating Hemiplegia of Childhood and Rapid-onset Dystonia Parkinsonism.