Overactivity, impulsivity and repetitive behaviour in males with fragile X syndrome: contrasting developmental trajectories in those with and without elevated autism symptoms

Background: Hyperactivity and repetitive behaviour are characteristic features of fragile X syndrome (FXS). However, little is known about the influence of autism symptomatology on how these characteristics develop over time. We investigate the profiles and developmental trajectories of overactivity, impulsivity and repetitive behaviour, in males with FXS over three time points spanning 8 years. Method: Participants formed two subgroups, those who displayed elevated symptoms of autism at Time 1 (n = 37; Mage = 16.32; age range = 6.61-43.51) and those who did not (n = 32; Mage = 8.43; age range = 8.94-47.49). Results: Participants without elevated symptoms of autism showed a reduction in impulsivity and repetitive questioning over time, whereas those with elevated symptoms of autism did not. Differences between the two subgroups in several topographies of repetitive behaviour emerged at Time 3 only. Conclusions: These results further understanding of the relationship between autistic phenomenology and behavioural characteristics in FXS