Increased T2 signal in the middle cerebellar peduncles on MRI is not specific for fragile X premutation syndrome.

The fragile X premutation tremor/ataxia syndrome (FXTAS) is a recently described adult-onset neurodegenerative disorder, in which ataxia, tremor, cognitive decline, parkinsonism, neuropathy and autonomic dysfunction occur in various combinations. It is reported to display a characteristic MRI appearance, with increased T2 signal in the middle cerebellar peduncles and around the dentate nuclei. Diagnostic criteria have been proposed on the basis of these clinical and radiological features, presupposing that a CGG expansion has been demonstrated. We present three cases in which MRI and clinical findings suggested the possibility of FXTAS, although only one was confirmed on genetic testing. The phenotypic overlap with multiple system atrophy of cerebellar type (MSA-C) and the importance of genetic confirmation are emphasised.