New challenges also exist for drug development. A single target might contribute genetic risk to only a small fraction (<1%) of patients, and a compound active against a single target might benefit only patients with that mutation. Hence, drug discovery for neuropsychiatric diseases could involve developing a catalogue of drugs targeting a variety of orphan diseases (Braun et al., 2010). More optimistically, one target gene might represent one component of a pathway that is dysregulated in a larger proportion of cases. Thus, the “orphan” drug designed to treat a rare disorder might turn out to have efficacy in a broader class of patients.
