Fragile X tremor/ataxia syndrome: Abbreviated FXTAS (pronounced fax-tass). A progressive neurological disorder that strikes men over age 50 and causes tremor, ataxia (balance problems) and dementia that become increasingly severe with age. These men may be misdiagnosed with Parkinson's or Alzheimer's disease. The disorder is due to a small mutation (premutation) in the same gene that causes fragile X syndrome, the most common cause of inherited mental retardation.
Men with FXTAS are usually born with normal intelligence but in their 50s develop intention tremor, parkinsonism, cognitive decline, and impotence. They have atrophy (shrinkage) of the brain. The premutation of the fragile X gene (FMR1) is evident on DNA analysis. FXTAS was first reported in 2001.