Self-injurious behaviour is purportedly common in autism, but prevalence rates have not yet been synthesised meta-analytically. In the present study, data from 14,379 participants in thirty-seven papers were analysed to generate a pooled prevalence estimate of self-injury in autism of 42% (confidence intervals 0.38–0.47). Hand-hitting topography was the most common form of self-injury (23%), self-cutting topography the least common (3%). Sub-group analyses revealed no association between study quality, participant intellectual disability or age and overall prevalence rate of self-injury. However, females obtained higher prevalence rates than males (p = .013) and hair pulling and self-scratching were associated with intellectual disability (p = .008 and p = .002, respectively). The results confirm very high rates of self-injury in autism and highlight within group risk-markers.

We evaluated the proportion of individuals with Down syndrome (DS: N = 108) who met criteria for autism spectrum disorder (ASD) on the Social Communication Questionnaire and the severity of ASD-related symptomatology in this group. The proportions of individuals with DS meeting the cut-off for ASD and autism in this sample were 19% and 8%, respectively. We then evaluated the behavioural profile of individuals with DS who scored above cut-off for ASD (DS+ASD; N = 17) compared with those with DS-only (N = 17) and individuals with idiopathic ASD (N = 17), matched for adaptive behaviour skills and ASD symptom severity (ASD group only). Individuals in the DS+ASD and ASD-only groups showed more stereotyped behaviour, repetitive language, overactivity and self-injury than the DS-only group (p < .001). Individuals in the DS+ASD and DS-only groups appeared less withdrawn from their surroundings than those with ASD (p < .004). These findings indicate differences in the behavioural and cognitive profile of individuals with DS+ASD compared with those with DS-only, when controlling for adaptive behaviour skills. Individuals with DS+ASD show broad similarities with individuals with idiopathic ASD with regard to ASD and behavioural characteristics but may also show some areas of subtle difference from this group.

This study provides the first meta-analysis of the purported differences in sleep time and sleep quality between people with and without intellectual disabilities. Twenty-one papers were identified that compared sleep time and/or sleep quality in people with and without intellectual disabilities. The meta-analysis of sleep time revealed that people with an intellectual disability slept for 18 min less, on average, than people without an intellectual disability. This significant difference was limited to those studies that tested groups of people with an identified genetic syndrome or developmental disorder. The analysis of sleep quality also concluded that people with intellectual disabilities experienced poorer sleep: In 93% of comparisons between groups, sleep was found to be of poorer quality in the group of people with intellectual disabilities. There were no differences found between studies that measured sleep objectively and those that used diary or questionnaire measures. Notably, most samples were drawn from populations of people with specified genetic syndromes or developmental disorders, rather than intellectual disability of heterogeneous origin. Similarly, most studies investigated sleep in children, although there was no evidence that the differences between the groups reduced during adulthood. Most studies used highly-regarded objective measures of sleep, such as polysomnography or actigraphy, although methodological flaws were evident in the identification of samples and the measurement of intellectual disability.

There are few studies documenting the persistence of self-injury in individuals with autism spectrum disorder (ASD) and consequently limited data on behavioural and demographic characteristics associated with persistence. In this longitudinal study, we investigated self-injury in a cohort of individuals with ASD over 3 years to identify behavioural and demographic characteristics associated with persistence. Carers of 67 individuals with ASD (Median age of individuals with ASD in years = 13.5, Interquartile Range = 10.00–17.00), completed questionnaires relating to the presence and topography of self-injury at T1 and three years later at T2. Analyses were conducted to evaluate the persistence of self-injury and to evaluate the behavioural and demographic characteristics associated with persistence of self-injury. At T2 self-injurious behaviour had persisted in 77.8 % of individuals. Behavioural correlates of being non-verbal, having lower ability and higher levels of overactivity, impulsivity and repetitive behaviour, were associated with self-injury at both time points. Risk markers of impulsivity (p = 0.021) and deficits in social interaction (p = 0.026) at T1 were associated with the persistence of self-injury over 3 years. Impulsivity and deficits in social interaction are associated with persistent self-injury in ASD and thus may act as behavioural risk markers. The identification of these risk markers evidences a role for behaviour dysregulation in the development and maintenance of self-injury. The findings have clinical implications for proactive intervention; these behavioural characteristics may be utilised to identify ‘at risk’ individuals for whom self-injury is likely to be persistent and therefore those individuals for whom early intervention may be most warranted.