Fragile X syndrome (FXS), is the most common cause of inherited mental impairment. This impairment can range from learning disabilities to more severe cognitive or intellectual disabilities (sometimes referred to as mental retardation). FXS is the most common known cause of autism or 'autistic-like' behaviour. Symptoms also can include characteristic physical and behavioural features and delays in speech and language development. This new book presents the latest research in this field.