Fragile X Syndrome, also known as Martin-Bell syndrome or Martin Bell-Renpenning syndrome is a syndrome comprising X-linked mental retardation in children with macroorchidism, prognathism, hypotonia and autism, and a characteristic but variable faces. It has an estimated incidence of 1 in 4000-9000 males and 1 in 7000-15 000 females.
It appears in boys (homozygous in the first year of life). In puberty there is pronounced growth of testes, abnormal speech pattern, large ears, long face, high-arched palate, and malocclusion. Additional abnormalities may include lordosis, heart defect, pectus excavatum, flat feet, shortening of the tubular bones of the hands, and joint laxity. Heterozygous females have a broad range of dysfunctions.