The Broader Autism Phenotype in Simplex and Multiplex Families

Thursday, May 17, 2012
Sheraton Hall (Sheraton Centre Toronto)
9:00 AM
J. Gerdts1, R. Bernier1, K. Ankenman1 and G. Dawson2, (1)University of Washington, Seattle, WA, (2)University of North Carolina, Autism Speaks, UNC Chapel Hill, Chapel Hill, NC, United States
Background:  Non-inherited genetic mutations are particular risk factors in single incidence, or simplex, autism spectrum disorder (ASD) families compared to multiplex ASD families.  Behavioral genetic studies examining the broader autism phenotype (BAP) document increased presence of BAP traits in multiplex ASD parents and siblings compared to simplex first-degree relatives. 

Objectives:  To compare the BAP in simplex and multiplex ASD families.

Methods:  Mothers, fathers, and siblings from 87 multiplex and 41 simplex ASD families were assessed using the Broader Phenotype Autism Symptom Scale (BPASS).  The BPASS is a semi-structured interview intended to assess ASD-related traits in four domains: Social Interest, Expressiveness, Conversational Skills, and Flexibility/Restricted Interests.  It combines information from self- and parent- report using clinical interview questions as well as direct observation.  Multiplex families were recruited from participants in a CPEA network funded genetics study of autism and simplex families were recruited from the Simons Simplex Collection.

Results:  Significant differences were found in mean levels of social interest between simplex and multiplex mothers, t(123) = -2.51, p = .01, Cohen’s d = 0.48, and fathers, t(109) = -2.15, p = .03, Cohen’s d = 0.42, with a trend in differences observed in siblings, t(96) = -1.81, p = .07, Cohen’s d = 0.38.  Simplex family members showed increased social interest across the three groups. Simplex mothers were significantly more expressive in their use of nonverbal communication compared to multiplex mothers, p = .006, as were simplex fathers, p = .006, and siblings, p < .001. Conversational skills were also improved  in simplex fathers, p = .04, and siblings, p = .008, compared to multiplex fathers and siblings. A significantly lower percentage of simplex family members were rated as having low to very low social interest compared to multiplex family members , X2(1, N = 334) = 14.42, p < .001.  Simplex siblings showed significantly lower rigidity and intense interests compared to multiplex siblings, t(96) = -2.30, p = .02, Cohen’s d = 0.48, and were less often rated as having impairing repetitive behaviors compared to multiplex siblings, 5% versus 21%, X2(1, N = 98) = 5.10, p = .02.  Simplex mothers and fathers did not differ in their flexibility and range of interests from multiplex mothers and fathers. 

Conclusions:  The decreased number and intensity of BAP traits observed in parents and siblings within simplex families provide behavioral support to findings of increased de novo genetic events not shared by other family members since ASD-related behavioral traits were shared less frequently in simplex compared to multiplex families. Thus, these behaviorally based findings suggest that the types of genetic causes of ASD may vary between single-incidence and multiple-incidence families and that multiplex family members are more vulnerable to ASD symptoms given shared genetic variance.

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