An Examination of the Broader Autism Phenotype in Simplex and Multiplex Families
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Non-inherited genetic mutations are more prevalent in families with only one individual diagnosed with autism spectrum disorder (ASD; simplex) whereas inherited genetic risk factors may play a greater role in families with more than one affected individual (multiplex). Behavioral genetic studies examining the broader autism phenotype document increased presence of BAP traits in first-degree relatives from multiplex versus simplex families. Mothers, fathers, and siblings from 87 multiplex and 41 simplex were included in analyses. In general, findings supported a differential presentation of behavioral features of the broader autism phenotype in family members from multiplex families compared to simplex families. This was particularly relevant in social communication skills. Multiplex family members showed decreased social interest, more impaired nonverbal communication abilities, and less flexible conversation skills compared to simplex family members. Effects were moderate to large across skill areas and were most consistently observed in siblings, followed by fathers, and then mothers. Cognitive profiles presented differently in parents compared to siblings. Specifically, differences between multiplex and simplex families in cognitive measures such as cognitive variability, face memory, and phonological processing were absent in parents, but were apparent in siblings. Multiplex siblings showed greater cognitive variability and were more likely to have impaired face memory and phonological processing skills compared to simplex siblings. Thus, multiplex siblings showed a number of similar elements of the cognitive phenotype in ASD in addition to social communication difficulties compared to simplex siblings. No relationship between the symptoms of the affected children and family member traits were found in the current study. Thus, increased symptom severity in affected children did not predict greater BAP traits in either simplex or multiplex families. Despite reports that macrocephaly appears to be a familial trait in ASD, head circumference measurements did not differ between multiple-incidence and single-incidence families. However, a positive relationship between head circumference and increased BAP traits was more pronounced in simplex siblings compared to multiplex siblings. Given the variability in predictions of increased head circumference and ASD symptoms in affected individuals, this finding was not predicted and it is difficult to interpret it in isolation. Further work is necessary to replicate this relationship. The decreased number and intensity of BAP traits observed in parents and siblings within simplex families provide behavioral evidence consistent with findings of increased de novo genetic events since ASD-related behavioral traits were observed less frequently in simplex compared to multiplex families. These behaviorally-based findings suggest that multiplex families may be more vulnerable to ASD symptoms given shared genetic variance.
- Psychology