Fragile X syndrome is considered the most common inherited cause of mental retardation in the general population. Fragile X syndrome affects males and females. The number of people carrying the fragile X gene may be as high as 1 in 625. Unlike many other genetic disorders, physical signs are not always apparent in a person affected with fragile X. Fragile X can be passed on in a family in which there are no signs of the condition. As a rule, the mother of an affected child is a carrier of the fragile gene.
Effects range from very mild to quite severe.
Problems may include learning disabilities, short attention span, hyperactivity, speech abnormalities and autistic-like behavior. Some of the physical features sometimes associated with fragile X syndrome are large or prominent ears, a long face with a protruding chin, and very extensible finger joints. Fragile X males usually also have enlarged testes after birth. Genes usually come in pairs, one from the mother and the other from the father, and are packaged into microscopically-visible chromosomes. Women have two X chromosomes in each body cell and men have one X chromosome and one Y chromosome.