An increased risk of developing FXTAS is inherited in an X-linked dominant pattern. The FMR1 gene is located on the X chromosome, one of the two sex chromosomes. (The Y chromosome is the other sex chromosome. ) The inheritance is dominant because one copy of the altered gene in each cell is sufficient to elevate the risk of developing FXTAS. In females (who have two X chromosomes), a mutation in one of the two copies of the FMR1 gene in each cell can lead to the disorder. In males (who have only one X chromosome), a mutation in the only copy of the gene in each cell can result in the disorder. However, not all people who inherit an FMR1 premutation will develop FXTAS. In X-linked dominant disorders, males typically experience more severe symptoms than females. Fewer females than males develop FXTAS because the X chromosome that contains the premutation may be turned off (inactive) due to a process called X-inactivation. Early in embryonic development in females, one of the two X chromosomes is permanently inactivated in somatic cells (cells other than egg and sperm cells). X-inactivation ensures that females, like males, have only one active copy of the X chromosome in each body cell. Usually X-inactivation occurs randomly, so that each X chromosome is active in about half the bodys cells. Sometimes X-inactivation is not random, and one X chromosome is active in more than half of cells. When X-inactivation does not occur randomly, it is called skewed X-inactivation. Researchers suspect that the distribution of active and inactive X chromosomes may help determine the severity of FXTAS in females or whether they develop signs and symptoms of the condition. 
Is fragile X-associated tremor/ataxia syndrome inherited ?