Autism Traits in Extended Family Members

Background: The broad autism phenotype (BAP) is a well-established construct that reflects the presence of sub-threshold ASD traits in non-affected relatives of individuals with ASD. BAP traits are (a) increased in parents of individuals with ASD compared to parents of individuals from non-ASD and (b) more frequent in parents of individuals from multiplex families vs. simplex families. The BAP has been assessed using the Broad Autism Phenotype Questionnaire (BAP-Q; Hurley et al 2007; Sasson et al 2013) and the Social Responsiveness Scale-Adult Research Version (SRS:ARV, Constantino 2005). For this study, we investigated the presence of BAP traits among parents from extended ASD families (i.e., ASD occurs in multiple generations and cousin pairs). 

Objectives: This study evaluated BAP traits in parents of individuals with ASD in extended ASD pedigrees. Our hypothesis is that parents (connecting relatives of cousin pairs) from extended ASD families would demonstrate increased scores on measures of ASD traits compared to parents from simplex families.

Methods: 43 parents of individuals with ASD (25 mothers/18 fathers) from extended pedigrees (EXT) were evaluated as part of a larger study of ASD genetics. All parents were from single branches within larger pedigrees and completed the BAP-Q and SRS:ARV as part of a multi-trait evaluation protocol. Parental scores on these measures were compared to those from the Simons Simplex Collection (SSC; N=2616 mothers and fathers) using either a t-test for independent samples or the Wilcoxon signed rank sum test.  

Results: Mean [sd] BAP-Q Total scores for the two groups (BAP-Q Total EXT=4.42 [2.13], SSC 1.75 [.43]) differed significantly (unpooled variances t-test p<0.0001). BAP-Q subscores (Aloof p<0.0002), Pragmatic p<0.0001, Rigid p<0.0001) also were significantly higher in the EXT parents. Comparison of maternal and paternal EXT and SSC mean BAP-Q showed a similar pattern of results as EXT maternal and paternal BAP-Q means were significantly higher than SSC means with the exception of the maternal Aloof subscore (p=0.17). Mean SRS Total scores and subscores for the EXT and SSC groups did not differ significantly; this same pattern was observed when comparing maternal SRS scores for the EXT and SSC groups. However, paternal Total SRS scores were higher among EXT fathers (p=.019). In addition, paternal means for the Motivation (p=.014), Communication (.036), and Cognition subscales were significantly higher in the EXT fathers.

Conclusions: Sub-threshold autism traits as measured by the BAP-Q are significantly greater in parents of individuals with ASD from extended pedigrees. However there is limited evidence that these same parents are more impaired on the SRS:ARV. This may reflect different degrees of “sensitivity” to ASD impairments and is in line with findings showing that the BAP-Q detected greater numbers of parents with sub-threshold impairments vs. the SRS:ARV (Davidson et al 2014). The presence of elevated BAP-Q scores in parents from extended ASD adds to the evidence that such families are enriched for ASD and related traits and should continue to be a focus of genetic studies.