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Fragile X

Fragile-X associated tremor/ataxia (FXTAS)

FXTAS is a very common tremor/ataxia syndrome, which is newly described (as of 2001). It is a late-onset disorder, typically beginning in the 60's or 70's, with involvement of multiple systems -- gait ataxia, intention tremor, peripheral neuropathy, autonomic dysturbance, and sometimes dementia.

FXTAS may affect as many as 1/3000 men over the age of 50. (Hall et al, 2005). About 3% of persons being tested for hereditary cerebellar disorders are positive for FXTAS. Very few people are tested because there is no treatment.

Diagnosis:

This is a diagnosis to consider in men with ataxia and tremor. MRI shows atrophy, white matter changes in the corpus callosum, and distinctive T2 hyperintensities in the middle cerebellar peduncles. There are three phenotypes -- essential tremor like (35%), cerebellar (29%), and parkinsonian (12%)

Genetics:

FXTAS is an X-linked disorder. There are 55-200 CGG repeat expansions in the FMR1 gene. Full mutations cause the Fragile X syndrome, which is much more severe.

Males transmit this gene to all of their daughters. Thus the inheritance pattern of the disease itself goes from father->daughter->male children. Female carriers (the daughters) have a 50% chance of transmitting the gene to each child (male or female).

Proposed criteria for genetic testing for (FMR1) are:

fragile x
High signal seen in both middle cerebellar peduncles in person with Fragile X associated tremor ataxia.

Treatment:

There is no treatment, but genetic counseling may be helpful. For example, daughters of a man with FXTAS may benefit from the knowledge that they are a carrier, and that 50% of their male offspring may have FXTAS. Similarly, 50% of their female offspring may be carriers.

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Copyright August 3, 2016 , Timothy C. Hain, M.D. All rights reserved. Last saved on August 3, 2016