 FMR1 is a gene associated with fragile X syndromethe most common cause of mental retardationand with social, emotional, and cognitive deficits. The chance of developing these deficits depends on the number of times the FMR1 gene is repeated on the X chromosome. Individuals with more than 200 copies of the FMR1 gene have the full fragile X mutation, putting them at most risk for mental retardation. Individuals with between 55 and 200 copies of the FMR1 gene have the fragile X premutation; they are much less likely to develop mental retardation, but they may have subtle social, emotional, and cognitive deficits and their children are more likely to have the full fragile X mutation. A theory, which this study will test, holds that the deficits of people with the fragile X premutation are caused by dysfunction in the limbic system. The limbic system consists of a group of structures in the brain that govern emotions and behavior. This study will examine people with the fragile X premutation to determine whether and to what extent they have emotional, social, and memory deficits. The study will also determine whether changes in fragile X gene function are related to increased deficits and how the brain, and specifically the limbic system, may be involved in these deficits. 