Damaging mutations in Syngap1 that reduce the number of functional proteins are one of the most common causes of sporadic intellectual disability and are associated with schizophrenia and autism spectrum disorder. Early estimates suggest that these non-inherited genetic mutations account for two to eight percent of these intellectual disability cases. Sporadic intellectual disability affects approximately one percent of the worldwide population, suggesting that tens of thousands of individuals with intellectual disability may carry damaging Syngap1 mutations without knowing it.