Fragile X syndrome (FXS), also known as Martin-Bell syndrome, or Escalante's syndrome (more commonly used in South American countries), is a genetic syndrome. Nearly half of all children with fragile X syndrome meet the criteria for a diagnosis of autism. It is an inherited cause of intellectual disability especially among boys. It results in a spectrum of intellectual disabilities ranging from mild to severe as well as physical characteristics such as an elongated face, large or protruding ears, and large testicles (macroorchidism), and behavioral characteristics such as stereotypic movements (e.g. hand-flapping), and social anxiety.