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Fragile X

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VOL: 101, ISSUE: 21, PAGE NO: 28

What is fragile x?

What is fragile x?
Fragile X is a genetic condition with a variety of manifestations, including Fragile X syndrome. Fragile X syndrome is the most common cause of genetically-inherited mental impairment, ranging from mild learning to severe intellectual difficulties, including autism.

Fragile X syndrome also results in physical abnormalities and behavioural deficits, and can affect speech and language development. It can also cause Fragile X-associated tremor ataxia syndrome, a balance, tremor and memory condition that affects some older male carriers as well as causing problems for female carriers such as premature ovarian failure.

Fragile X can be passed on to family members by carriers with no obvious sign of the condition.

In some families it is a long-term problem affecting generations. In other families only one person may be affected.

Causes
Fragile X is caused by the absence of a functional fragile X gene on the X chromosome. This mutation halts production of the familial mental retardation protein (FMR1), which helps to develop neuronal pathways in the brain. These pathways are responsible for cognitive development.

Fragile X is an inherited condition. Male carriers pass the premutation to female children, but not to males. Each child of a female carrier has a 50 per cent chance of inheriting the gene. The premutation can be passed through generations of one family before a child is affected.

Symptoms
Features of Fragile X:

- Mental difficulties, from learning disabilities to mental retardation;

- Autistic behaviour;

- Attention deficit and hyperactivity;

- Anxiety and unstable mood;

- Hyperextensible joints;

- Physical abnormalities, such as elongated face, abnormally large ears and flat feet;

- Epilepsy affects about a quarter of people with Fragile X.

Males are usually more severely affected than females. While most male children with the condition have mental retardation, only a third to half of girls experience significant intellectual impairment.

Emotional and behavioural problems, including anxiety and attention deficit hyperactivity disorder, and psychosis and obsessive-compulsive disorder, are common in both sexes.

About one-fifth of boys with Fragile X are diagnosed with autism and most boys and some girls will have some symptoms of autism.

Diagnosis
A DNA-based blood test is used to diagnose both carriers of Fragile X and fully affected individuals. As symptoms can be subtle, some health care practitioners recommend testing be considered for any individual with inexplicable developmental problems or mental retardation.

Treatment
There is no cure for Fragile X and although appropriate education and medication can help maximise potential, most boys and many girls remain affected throughout their lives.

Medication can improve attention span and reduce hyperactivity. Early intervention and intervention programmes, including speech and physical therapy, can be useful.

The FMR protein normally assists in the development of the connections between neurons that underpin learning and memory. Because the absence of the protein seems to delay their development rather than destroy them, it is hoped that research can identify a treatment that will encourage neuron development.

Research is also being done into gene therapy - to determine whether a healthy replacement gene could be inserted into the cells affected by Fragile X - and protein replacement therapy.

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