Abstract
BackgroundThe limited behavioural phenotype literature on Phelan–McDermid syndrome (PMS) indicates atypically high levels of activity, impulsivity and autism spectrum disorder (ASD) behaviours. Divergent profiles of ASD in PMS are also reported, with some studies demonstrating similarities to idiopathic ASD and others indicating an uneven profile of social and communication impairments and repetitive behaviours. An evaluation of the behavioural phenotype of PMS and the prevalence and phenomenology of ASD is warranted, particularly given the causal involvement of the SHANK3 gene in the aetiology of PMS.MethodsCarers of individuals with PMS (N = 30; mean age = 10.55, SD = 7.08) completed questionnaires relating to impulsivity, overactivity, mood, interest and pleasure, repetitive behaviour and ASD phenomenology. These data were compared to data from matched samples of individuals with fragile X and Down syndromes and idiopathic ASD. In order to evaluate the profile of ASD phenomenology in PMS, two comparisons were made: first, including the total sample with PMS, and second, including only those who met the threshold indicative of autism on an ASD screening measure.ResultsThe results revealed lower mood in individuals with PMS, but no differences in impulsivity and overactivity. Compulsive and routine-driven repetitive behaviours were less common in the total sample with PMS; however, motor-based stereotyped behaviours were more common. ASD phenomenology was highly prevalent, with 87% of the sample meeting the cutoff score for ASD and 57% meeting the cutoff for autism. The profile of ASD phenomenology in the total sample with PMS differed from those with idiopathic ASD across impairments in communication and social interaction and repetitive behaviour. However, the profile of those who met the threshold for autism was commensurate to those with idiopathic ASD.ConclusionsASD phenomenology is common within PMS. Whilst the total sample may display an atypical profile of ASD behaviour, the profile in those who met the threshold for autism was very similar to those with idiopathic ASD. These results are discussed in relation to the wider behavioural phenotype and the emerging evidence of an autism endophenotype in PMS.
Highlights
The limited behavioural phenotype literature on Phelan–McDermid syndrome (PMS) indicates atypically high levels of activity, impulsivity and autism spectrum disorder (ASD) behaviours
Whilst the total sample may display an atypical profile of ASD behaviour, the profile in those who met the threshold for autism was very similar to those with idiopathic ASD
Behavioural phenotype of PMS In order to fulfil the first aim of the study, delineating the behavioural phenotype of PMS, compared to the matched contrast groups, subscale scores were derived to describe mood, activity levels and repetitive behaviour
Summary
The limited behavioural phenotype literature on Phelan–McDermid syndrome (PMS) indicates atypically high levels of activity, impulsivity and autism spectrum disorder (ASD) behaviours. Recent research has demonstrated that the SHANK3 mutation results in neuronal changes, including increase in input resistance to excitability, some impairment in dendritic branching and decreases in synaptic transmission [7]. These changes are mechanistically linked to impairments in hyperpolarization-activated cation (Ih) channels, with a suggestion that reduced Ih currents may account for some of the phenotypic characteristics observed in PMS [7]. Preliminary research suggests that the physical features and severity of intellectual disability correlate with the size of the genetic deletion. Expressive speech deficits are not associated with the size or type of deletion [8]
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