Does Family Affectedness Predict Outcomes in Infants at Risk for Autism?

Background: Infant siblings of children with an autism spectrum disorder (ASD) are more likely to develop an ASD when compared to siblings of typically developing children (e.g., Landa, Holman, & Garrett-Mayer, 2007).  Although the mechanisms for this risk are largely unknown, genetic factors are often implicated. The broader autism phenotype (BAP) is a constellation of subclinical behaviors associated with ASD that can be found in non-autistic family members. The BAP includes differences in social interactions, relationships, communication skills, and restricted patterns of behavior or intense interests.  The BAP is thought to be an index of family genetic risk for autism (Piven, 2001).

Objectives: Within this study, the presence of ASD and BAP in family members or ‘family affectedness’ is explored as a predictor of infants developing an ASD, BAP behaviors or other developmental concerns. 

Methods: As part of a larger longitudinal study, these analyses included seventy-five infant siblings from families raising one child (simplex families; n = 68) or more than one child (multiplex families; n = 7) with an ASD.  At 24 or 36 months of age the enrolled infant siblings were categorized as typically developing (56%), with an ASD (12%), with behaviors consistent with the social deficits of the BAP (16%), or other developmental concerns (16%).  Family affectedness was conceptualized as the number of first degree family members with either an ASD or the social/communication features associated with the BAP (as measured by the Social Responsiveness Scale). Approximately 12% of fathers, 13% of mothers, 9% of male siblings, and 11% of female siblings had social/communication differences consistent with the BAP.

Results: Regression analyses assessed if a family history of ASD and/or BAP behaviors could predict which infant siblings would themselves develop an ASD, BAP behaviors, or other developmental concerns (while controlling for family size).  Paternal social/communication deficits and family size predicted the occurrence of multiplex families, which, in turn predicted which infant siblings would develop an ASD.  In this study, infant siblings from multiplex families were seven times more likely to develop an ASD than infant siblings from simplex families.  Family size predicted the frequency of BAP and other developmental concerns, such that larger families had more members with BAP behaviors or other developmental concerns. 

Conclusions:   Broader phenotype features in fathers were more common in multiplex families and infants of multiplex families were more likely to develop an ASD.  This research suggests that early monitoring and intervention services designed for this at-risk population should assess and support family social/communication skills to identify infants at elevated risk and to promote optimal parent-child interactions - the proximal context for child development.