Placebo Response in Fragile X-associated Tremor/Ataxia Syndrome

Background: Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder characterized by intention tremor, cerebellar ataxia, and executive dysfunction in carriers of a CGG repeat expansion premutation (55-200 repeats) in the fragile X mental retardation 1 (FMR1) gene. Given reports of poor insight in FXTAS, we postulated that patients with FXTAS would be less likely to exhibit placebo response.

Objective: To analyze placebo response from the first randomized controlled trial in FXTAS that evaluated cognitive and motor outcomes after 1 year of treatment with memantine.

Methods: Data from the placebo arm of the first randomized controlled trial in FXTAS were analyzed. There were 2 coprimary outcomes. Based on studies in Parkinson's disease, placebo responders were defined as individuals with an improvement of at least 50% in the coprimary outcomes. Improvements of 20% and 30% served as secondary cutoff values based on the suggested magnitude of placebo response in other movement disorders.

Results: A total of 36 participants in the placebo group completed baseline and follow-up evaluations. The average age was 66 ± 7 years, and 60% were men. Average CGG repeat size was 86 ± 18. A total of 19 participants had stage 3 disease. Only 1 patient showed 50% improvement in both coprimary outcomes. At 30% and 20% improvement, there were 2 and 3 patients showing placebo response in the coprimary outcomes, respectively.

Conclusions: Patients with FXTAS exhibited low rates of placebo response in a randomized controlled trial. Further studies on the relationship between baseline insight and placebo responsivity are applicable to FXTAS and other disorders exhibiting cognitive impairment.