Fragile X is the most common known inherited cause of developmental disabilities. The name comes from the way the X chromosome looks under a microscope; the tip shows an abnormal gap that appears broken, called a ‘fragile site’.
Fragile X is due to an abnormality involving a single gene called FMR-1 that is situated on the X chromosome. There is an increase in size and some stretching in part of the gene that affects the way it works. In some men and women, with only a small expansion or stretch, they show no symptoms but are carriers of Fragile X. This small defect in FMR1 is called a premutation.Those with a larger expansion in FMR1, a full mutation, are affected by the syndrome. The gene switches off production of a protein FMRP. People who have the ‘mosaic’ form are partly affected, the protein is produced in some, but not all tissues.
The discovery of Fragile X
Fragile X was discovered in the late 1970s. In 1980 it was identified that people presenting with a group of mental and physical characteristics had a chromosomal abnormality. The gene responsible was identified by scientists in 1991.
The incidence of Fragile X
Studies estimate that around one in 2000 males are affected and roughly one in 4000 females of all races and ethnic groups. Studies indicate one in 259 women of all races carry Fragile X and one in 800 men. It is believed that this common genetic has yet to be diagnosed in 80 to 90 per cent of people with the syndrome.
Common symptoms of Fragile X
A person with full mutation Fragile X can exhibit a few or a lot of symptoms associated with this syndrome. They include:
Classic physical characteristics of Fragile X
These physical characteristics of Fragile X are noticable after the onset of puberity include:
Long face with a prominent jaw, prominent ears, large testicles, mostly after puberty.
People with Fragile X also are more prone to certain diseases. These include connective tissue problems, e.g. flat feet, loose joints, congenital hip dislocation, scoliosis (curvature of the spine), mitral valve prolapsed (heart valve), eye problems such as strabismus and squints.
