About 3% to 7% of the general population have neurodevelopmental and psychiatric disorders, including intellectual disabilities, autism spectrum disorder and schizophrenia. Genetic tests commonly performed in these patients identify in 10-15% of cases, mutations contributing to neurodevelopmental disorders. However, the effect of 90% of these mutations is not known because they are very rare. How the effects of these rare and unknown variants on a person's cognitive development be assessed?