brain, spinal cord, and nerve disorders
Fragile X–Associated Tremor Ataxia Syndrome
Introduction
Fragile X–associated tremor/ataxia syndrome is a genetic disorder that affects mostly men and causes tremor, loss of coordination, and deterioration of mental function. Fragile X–associated tremor/ataxia syndrome results from a genetic mutation. Tremors in the hands commonly develop first, followed by loss of coordination, slowed movements, decreased facial expression, and eventually dementia. Genetic testing can confirm the diagnosis. Primidone,propranolol, or drugs used to treat Parkinson disease can often relieve the tremors. (See also Overview of Movement Disorders .) 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. Men inherit an X chromosome from their mother and a Y chromosome from their father. If the X chromosome they inherit from their mother contains the abnormal gene that causes Fragile X–associated tremor/ataxia syndrome, they have the disorder, which is classified as an X-Linked Inheritance . In X-linked disorders, the symptoms are usually more severe in boys and men. The presence of another X chromosome in girls and women may help protect them. A more extensive (full) mutation in this gene results in 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). However, 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. 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. 