Cognitive function impacts gait, functional mobility and falls in fragile X-associated tremor/ataxia syndrome

Abstract

Background: Executive function and information processing speed deficits occur in fragile X premutation carriers (PMC) with and without fragile X-associated tremor/ataxia syndrome (FXTAS). Gait is negatively impacted by cognitive deficits in many patient populations resulting in increased morbidity and falls but these relationships have not been studied in FXTAS.

Research question: We sought to investigate the associations between executive function and information processing speed and gait, turning and falls in PMC with and without FXTAS compared to healthy controls.

Methods: Global cognition and the cognitive domains of information processing speed, attention, response inhibition, working memory and verbal fluency were tested with a neuropsychological test battery in 18 PMC with FXTAS, 15 PMC without FXTAS, and 27 controls. An inertial sensor based instrumented Timed Up and Go was employed to test gait, turns and functional mobility.

Results: Lower information processing speed was significantly associated with shorter stride length, reflecting slower gait speed, in PMC with FXTAS (p = 0.0006) but not PMC without FXTAS or controls. Lower response inhibition was also significantly associated with slower turn-to-sit times in PMC with FXTAS (p = 0.034) but not in those without FXTAS or controls. Lower information processing speed (p = 0.012) and working memory (p = 0.004), were significantly correlated with a greater number of self-reported falls in the past year in FXTAS participants.

Significance: This is the first study demonstrating that worse executive function and slower information processing speed is associated with reduced gait speed and functional mobility, as well as with a higher retrospective fall history in participants with FXTAS. This information may be important in the design of cognitive and motor interventions for this neurodegenerative disorder.

Keywords: Cognitive function; Fall risk; Fragile X-associated tremor/ataxia syndrome (FXTAS); Gait and functional mobility; Instrumented Timed Up and Go (i-TUG).

Figure 1:

Spearman’s correlations between A) SDMT, B) Digit Span Backwards and C) FXTAS-RS scores and the number of self-reported falls occurring in the past year in FXTAS subjects (n=18). Key: SDMT, Symbol Digit Modalities Test; FXTAS-RS, fragile X-associated tremor/ataxia syndrome rating scale. The SDMT and Digit Span scores were scaled to age and years of education.