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Fragile X–Associated Tremor/Ataxia Syndrome
Fragile X–associated tremor/ataxia syndrome is a genetic disorder that affects mostly men and causes tremor, loss of coordination, and dementia.
The disorder results from a genetic mutation.
In men over 50, tremors in the hands develop first, followed by loss of coordination, slowed movements, decreased facial expression, and sometimes memory loss.
Genetic testing can confirm the diagnosis.
Primidone, propranolol, or drugs used to treat Parkinson disease can often relieve the tremors.
Fragile X–associated tremor/ataxia syndrome may affect as many as 1 of 3,000 men over 50.
Fragile X–associated tremor/ataxia syndrome results from a less extensive abnormality (called a premutation) in a gene on the X chromosome (one of the sex chromosomes). Men have an X and a Y chromosome, and women have 2 X chromosomes. A more extensive (full) mutation in this gene results in Fragile X syndrome (which causes intellectual disability) in children. People with the premutation are considered carriers (people who have an abnormal gene for a disorder but do not have the symptoms of the disorder). Men with the premutation pass it to their daughters (but not to their sons). Most women with the premutation are unaffected and thus may unknowingly pass the gene on to their sons (grandsons of men with the premutation). Children of such a woman have a 50% chance of inheriting the premutation. When the premutation is passed from mother to child, it sometimes changes into a full mutation, causing Fragile X syndrome in the child.
About 30% of men with the premutation and fewer than 5% of women with the premutation develop Fragile X–associated tremor/ataxia syndrome as adults. The risk of developing the disorder increases as people age.
Symptoms usually develop during late adulthood. The first symptom is often tremors in the hands, typically when people try to do a task. Other symptoms include loss of coordination, slow movements, stiffness, and decreased facial expression.
People may have problems remembering recent events and solving problems. They may think more slowly. These problems often progress to dementia. People may also have personality changes. They may become depressed, anxious, impatient, hostile, and moody.
Sensation in the feet may be lost. Internal organs may malfunction. Affected people may feel light-headed when they stand because blood pressure does not increase as it normally does (called orthostatic hypotension). They may have to urinate more frequently. Eventually, they may lose control of the bladder and bowel movements.
After symptoms appear, people may live from about 5 to 25 years.
In women with the premutation, symptoms are usually less severe, possibly because they have another X chromosome, which seems to protect against the effects of the X chromosome with the premutation. Women with the premutation are more likely to have early menopause and infertility problems than women without it.
Because this disorder was identified relatively recently (in 2001), the diagnosis is sometimes missed or mistaken for disorders that cause similar symptoms, such as Parkinson disease or Alzheimer disease. The tremors may be mistaken for essential tremor (a common tremor disorder that rarely causes any other symptoms—see Causes).
If doctors suspect the syndrome, they ask about symptoms in family members, particularly whether grandchildren have intellectual disability or daughters have had early menopause or infertility problems. When doctors examine children with Fragile X syndrome, they should find out whether the grandfathers have any symptoms suggesting Fragile X–associated tremor/ataxia syndrome.
Genetic testing can confirm the diagnosis. Magnetic resonance imaging (MRI) may be done to check for characteristic abnormalities in the brain.
Daughters and grandsons of men with Fragile X–associated tremor/ataxia syndrome should have genetic counseling. Daughters can be tested for the premutation so that they can make decisions about whether or not to have children and whether or not to have prenatal testing if pregnancy occurs.
Tremors can often be relieved by primidone (an anticonvulsant), propranolol (a beta-blocker), or many of the drugs used to control tremors due to Parkinson disease (see Table: Drugs Used to Treat Parkinson Disease).
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