Goal-directedness deficit in Huntington's disease

Abstract

Apathy and impulsive behaviour co-occur in Huntington's disease (HD), but these debilitating behavioural syndromes are multidimensional constructs, raising the question of which specific dimensions drive this relationship and the stability of the co-occurring dimensions across time. People with HD and controls completed multidimensional apathy and impulsive behaviour scales at baseline and 1-year follow-up. A principal component analysis was performed on pooled data (n = 109) to identify components and factor loadings of subscales. Linear mixed models were used to examine differences in components between groups and timepoints. Three meaningful components emerged. Component 1 comprised positive loading for dimensions of apathy and impulsive behaviour pertaining to goal-directedness, namely attention, planning, initiation, and perseverance. In contrast, other dimensions of apathy and impulsive behaviour loaded onto components two and three in opposite directions. People with HD only scored worse than controls on the goal-directedness component. All components remained stable over time and closely resembled factors from the five-factor personality model. Component 1 mapped onto the factor conscientiousness, component 2 to extraversion, and component 3 to neuroticism. The clinical overlap between apathy and impulsive behaviour in HD relates to goal-directedness, whilst other dimensions of these constructs did not overlap.

Keywords: Apathy; Dimensions; Five-factor model; Goal-directedness; Huntington’s disease; Impulsive behaviour.

Fig. 1

Baseline characterisation of the HD cohort. A) Distribution of CAP scores; B) Total functional capacity (TFC) scores; C) Unified Huntington’s disease rating scale – total motor scores (UHDRS-TMS); D) Symbol digit modality test (SDMT) scores; E) Montreal cognitive assessment (MoCA) scores. Inset shows number of control and HD participants and age distributions. To note, the relationships depicted in these plots are for visual display purposes only

Fig. 2

Components from apathy and impulsive behaviour subscales. Component 1 captured a core overlap between dimensions of apathy and impulsivity related to goal-directedness (attention, planning, initiation and perseverance), with loadings in the same direction. In contrast, components 2 and 3 did not demonstrate overlap between apathy and impulsivity dimensions. Rather, the various apathy and impulsivity dimensions loaded in opposite directions onto these components. Direction of arrows indicates worsening of the construct (more apathetic, more impulsive)

Fig. 3

Individual scores on components. Component scores for people with Huntington’s disease (blue) and healthy controls (grey), collapsed across timepoints. A) Component 1 captured a core overlap between dimensions of apathy and impulsivity related to goal-directedness (attention, planning, initiation and perseverance) with higher scores indicating reduced (worse) goal-directedness. In contrast, components two (B) and three (C) did not demonstrate overlap between apathy and impulsivity dimensions, but rather, the various apathy and impulsivity dimensions loaded in opposite directions onto these components. **p < 0.01

Fig. 4

Individual component scores over 1 year. Individual scores for the first 3 principal components at baseline and 1 year follow-up, plotted for people with Huntington’s disease (blue) and healthy controls (grey). People with Huntington’s disease scored significantly higher (worse) on average on component 1 (Goal-directedness) compared to controls (p = 0.007) with no significant differences between groups on components 2 or 3. On average, components remained stable over time. Error bars show standard error of the mean

Fig. 5

Component score associations in Huntington’s disease. Linear mixed models were fitted to component scores in the HD group only (no controls), to examine associations with disease-related variables (motor disease severity (UHDRS-TMS), cognition (SDMT), CAP score, age and sex (age and sex not shown)). A) Goal directedness deficit was significantly associated with lower CAP scores in HD (p = 0.006) and male sex (not shown), but not motor disease severity or cognition; B) No disease variables predicted scores on component 2; C) No disease variables predicted scores on component 3, whilst male sex (not shown) was associated with higher scores (increased emotional blunting, non-reactive). To note, differences between controls and HD were evident on component 1 only. **p < 0.01

Fig. 6

Goal-directedness and motor disease severity in Huntington’s disease A) Baseline goal-directedness (component 1 scores) were not associated with change in motor disease scores (UHDRS-TMS) over 1 year. B) Change in goal-directedness (component 1 scores) over 1 year was not associated with change in motor disease scores