Objective: To compare Fragile X-associated tremor/ataxia syndrome (FXTAS), Parkinson disease (PD), essential tremor (ET) and controls using quantitative measures of tremor.

Background: FXTAS, a progressive neurodegenerative disease that affects carriers of a 55-200 CGG repeat expansion in the fragile X mental retardation 1 gene, is often initially diagnosed as PD or ET due to overlapping motor symptoms. Tremorography has the capacity to quantitatively measure various aspects of rest, intention and postural tremor, bradykinesia, and fine motor coordination, and has been shown to significantly correlate with clinical tremor rating scales and have utility in quantitative assessments when combined with standard clinical assessment.

Methods: Subjects with FXTAS (n = 21; mean age 69.9 ± 7.9 years), PD (n = 23; mean age 71.3 ± 7.9 years) and ET (n = 20; mean age 69.8 ± 8.8 years) and controls (n = 20; mean age 62.7 ± 8.5 years) underwent quantitative tremor testing using the ETSenseTM sensor with the Kinesia HomeViewTM system. Tremor was evaluated in both upper extremities during a series of motor tasks. Penalized multinomial logistic regression was used to determine whether tremor measures could distinguish between groups. Response inhibition, verbal fluency, and information processing speed were measured to investigate whether cognitive domains were associated with tremor.

Results: FXTAS had greater kinetic tremor than PD (p = 0.05) and increased bradykinesia compared to ET (p = 0.004). PD had worse bradykinesia compared to FXTAS and ET (p < 0.0001). In FXTAS, PD and ET, slower information processing speed and verbal fluency were associated with worse dysrhythmia and bradykinesia (p = 0.03 to 0.003), as well as worse kinetic tremor in PD and ET (p = 0.009 and 0.01, respectively) and worse rest and postural tremor in ET (p = 0.01 to 0.004). Right hand finger tap speed distinguished FXTAS from ET and combined rapid alternating movements amplitude distinguished FXTAS from PD in the regression model (p < 0.0001).

Conclusions: This is the first quantitative study demonstrating 1) distinct tremor and bradykinesia profiles in FXTAS, PD, and ET which if confirmed could be used to distinguish these movement disorders, and 2) significant associations between cognition and tremor in FXTAS.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/fragile-x-associated-tremor-ataxia-syndrome-parkinsons-disease-and-essential-tremor-subjects-demonstrate-distinct-tremor-characteristics-using-quantitative-tremorography/