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The Neurocognitive Profile of Individuals with Phelan Mcdermid Syndrome (PMS): Comparison with Autism Spectrum Disorder (ASD) and Individual Differences.
Phelan-McDermid Syndrome (PMS) is a rare neurodevelopmental condition caused by a chromosome 22q13.3 deletion. Individuals have mild to profound learning disabilities and 70-80% also have autism spectrum disorder (ASD). Little is known about the shared cognition of PMS and ASD or individual differences within PMS.
Objectives:
To investigate three early processes often disrupted in ASD; spontaneous social attention, biological motion, and visual attention shifting. First, we examined mean group differences and individual variability. Second, we used hierarchical clustering to identify subgroups based on performance profiles across domains. Third, we investigated the relationship between neurocognitive performances, ASD symptoms, and developmental delay.
Methods:
22 PMS (2-19 years), 27 ASD (2-19 years) and 28 typically developing (TD) individuals (1.6-6 years) completed a series of eye-tracking (ET) and behavioural tasks. Spontaneous social attention was measured with a face pop-out ET task and a social orienting behavioural task. Biomotion was measured using a point-light display ET task, and visual attention shifting (disengagement time) with the Gap Overlap (ET) task. Autistic symptoms were assessed in PMS and ASD using the ADOS and ADI-R, and level of adaptive function for all using the Vineland Adaptive Behaviour Scale. Non-verbal mental age (NVMA) was estimated using developmentally appropriate tests. Developmental delay was calculated as chronological age/NVMA.
Results:
Social orienting differed by group (F(2,66) = 7.298, p = .001), with a higher percentage of orienting to social versus object sounds in TD (p = .001) and ASD (p = .001) versus PMS. 59% of PMS participants showed preference for social orienting, 12% for object orienting, 18% had no preference, and 12% did not orient to either stimuli. Social orienting was positively related to social adaptive functioning (r(63) = .438, p < .001) across groups, and negatively to ASD symptom severity in PMS (r(17) = -.620, p = .008). Face pop-out effect (i.e., first look to face in >50% of trials) (45% in PMS, 43% in ASD, and 55% TD) and preference for Biomotion (PMS and ASD 53%, TD 57%) did not differ between groups, but 88% (6/7) of PMS had longer disengagement times than the average ASD or TD individual.
Hierarchical clustering applied to 40 participants with data across all tasks revealed 3 clusters (stability of >.75 after 1,000 bootstraps). Cluster 1 (3 PMS, 3 ASD, and 4 TD) contained the longest disengagement times on average, cluster 2 (1 PMS, 8 ASD, and 5 TD) the highest social attention/orienting preference, and cluster 3 (1 PMS, 2 ASD and 13 TD) the fastest disengagement and lowest social attention. Cluster 1 had on average the lowest NVMA, highest ASD symptom severity and lowest social adaptive functioning. Cluster 2 had the most developmental delay and cluster 3 had the least developmental delay and highest social adaptive functioning.
Conclusions:
PMS individuals performed similarly to ASD on ET tasks of social attention but had lower rates of social orienting relating to ASD symptom severity, and longer disengagement times. No performance profile distinguished ASD and PMS groups as individual performance varied within both groups.