What are the genetic changes related to fragile X-associated tremor/ataxia syndrome ?
Mutations in the FMR1 gene increase the risk of developing FXTAS. The FMR1 gene provides instructions for making a protein called FMRP, which helps regulate the production of other proteins. FMRP plays a role in the development of synapses, which are specialized connections between nerve cells. Synapses are critical for relaying nerve impulses.  Individuals with FXTAS have a mutation in which a DNA segment, known as a CGG triplet repeat, is expanded within the FMR1 gene. Normally, this DNA segment is repeated from 5 to about 40 times. In people with FXTAS, however, the CGG segment is repeated 55 to 200 times. This mutation is known as an FMR1 gene premutation. An expansion of more than 200 repeats, a full mutation, causes a more serious condition called fragile X syndrome, which is characterized by intellectual disability, learning problems, and certain physical features.  For unknown reasons, the premutation leads to the overproduction of abnormal FMR1 mRNA that contains the expanded repeat region. The FMR1mRNA is the genetic blueprint for the production of FMRP. Researchers believe that the high levels of mRNA cause the signs and symptoms of FXTAS. The mRNA has been found in clumps of proteins and mRNA (intranuclear inclusions) in brain and nerve cells in people with FXTAS. It is thought that attaching to FMR1 mRNA and forming clumps keeps the other proteins from performing their functions, although the effect of the intranuclear inclusions is unclear. In addition, the repeat expansion makes producing FMRP from the mRNA blueprint more difficult, and as a result, people with the FMR1 gene premutation can have less FMRP than normal. A reduction in the protein is not thought to be involved in FXTAS. However, it may cause mild versions of the features seen in fragile X syndrome, such as prominent ears, anxiety, and mood swings.