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Fragile-X Syndrome

By: Lucy Debenham BA (hons) - Updated: 14 Oct 2012 | comments*Discuss
Fragile-x Syndrome Disability Genetic

Fragile-X syndrome is the most common inherited form of mental retardation. It results from a mutation on a single gene. Problems are caused when the mutated gene is unable to produce the needed amount of a protein used by the body's cells. It is especially damaging to brain cells. The severity of the condition is directly related to the amount of the protein that is produced. The syndrome is also known as Martin-Bell syndrome, named after the researchers who first described the disability (although its cause was not then known).


Since the genetic mutation that causes Fragile-X syndrome occurs on the X chromosome, fathers cannot pass the condition on to their sons. Keep in mind that males are XY while females are XX. The father contributes the Y chromosome. Therefore if a son has Fragile-X syndrome, the malfunctioning X was obtained from the mother. Mothers with Fragile-X have a 50 percent chance of passing it to their children.

Males with the syndrome have a high probability of severe intellectual disability. Females are usually less affected, as they have an additional "backup" copy of the X chromosome. However, females can be affected in the range from fully normal to severe intellectual disability. Since males and females are affected differently, this may explain the apparent "under diagnosis" of females with Fragile-X syndrome.


There is no cure for Fragile X. Physical, education and behavioural therapy can reduce the severity of some symptoms, while other expressions of the condition can be treated with medications. If treatment is started early, it can be more effective than waiting until later.

DNA testing for Fragile-X syndrome was introduced in 1992. Because symptoms can be subtle and prevalence is relatively high (1 in 4000 males, 1 in 6000 to 8000 females), it is important to test for Fragile-X when unexplained developmental delays or mental retardation are observed.


It has been observed that children with Fragile X are often quite good at imitation and tend to be highly social. This combination bodes well for the success of early intervention programmes. The more time a Fragile X child spends with children who are developing at a normal pace, the more benefit they can derive from the interaction.

Although females with Fragile-X syndrome often face difficulties in maths, they perform well with spelling and reading. They tend to prefer social isolation and may exhibit disabilities similar to schizophrenia. Males with Fragile-X have the potential to achieve higher levels than might be predicted from IQ. However, they tend to have difficulty with skills that require sequential processing of information (reading is an example). Fragile-X males often need to see the whole before they are able to understand the parts.

Teachers and parents should understand that children with Fragile-X syndrome are capable of achieving a level higher than expected based on measured IQ. Best results are usually obtained when these children are included in mainstream schools, provided that the classroom is an organized environment. Individualized assistance provided by trained inclusion teachers is also critical for success. Other effective strategies include cooperative learning situations and assistance from peers.

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