Fragile X syndrome is the most common cause of inherited learning disability. The effects range from subtle learning problems with an average IQ to severe learning disabilities. The behavioural features include a short attention span, being easily distracted, impulsive, restless and hyperactive. There may be difficulties in the areas of language, self-help, social interaction and understanding. Individuals with Fragile X syndrome appear normal at birth, but certain physical features associated with it may emerge later in childhood e.g. a largish head, a long narrow face, large ears, a prominent forehead, high-arched palates and dental overcrowding. Individuals with Fragile X syndrome are often hyperactive. Males particularly have a reputation for displaying challenging behaviour e.g. physical and verbal aggression. It is thought to affect approximately 1 in 2000 girls and one in 1250 boys; boys are usually more severely affected.