A Study of Siblings of Individuals with ASD: Comparison of Pragmatic Language Ability
Deficits in pragmatic language are commonly observed, not only in individuals with ASD, but also in siblings of individuals with ASD (Bishop, 1997; Baron-Cohen, 1988). These findings suggest pragmatic language impairment could be a heritable trait. Aside from shared genetics in siblings, environmental and gene x environment interactions could influence the development of pragmatic language. Specifically, having a sibling with ASD (who has general language impairment and specifically pragmatic language deficits) may influence the language environment of the sibling and their pragmatic ability. Examining pragmatic language in siblings of children with ASD is also critical because impairment in pragmatic language influences behavioral problems at school, mood, and willingness to engage in social interactions (Donno et al., 2010; Gilmour et al., 2004).
This study compared the overall score and the subscale scores on a measure of pragmatic language in a twin sample. Three comparison groups were included, which differed by the concordance of diagnosis with the proband: (1) ASD concordant twin (ASD Sib of ASD), (2) TD disconcordant twin (TD Sib of ASD) and (3) a reference group of TD siblings of TD probands was also included.
Groups included: 10 ASD Twin of ASD (Male=7, Female=3), 10 TD Twin of ASD (Male=2, Female=8) and 10 TD Twin of TD (Male=2, Female=8) between the ages of 7 and 16. Additionally, data from 10 ASD Sibs of ASD, 10 TD Sib of ASD, and 10 TD Sibs of TD have been collected but not analyzed. Groups were matched for age. Coders trained for reliability and blind to diagnosis viewed video-recordings of a child-experimenter interview to assess subjects’ pragmatic language using the Pragmatic Rating Scale-Modified (PRS-M) (Ruser et al., 2007). The PRS-M scored the subjects on verbal (e.g., clarity, referencing emotions, grammar) and non-verbal (e.g., eye contact, gestures) aspects of pragmatic language.
In the TWIN groups, there was no difference in PRS Sum of Scores between TD Twins of ASD (M = 8.90, SD = 3.54) and TD Twins of TD (M=7.60, SD=2.37). For the PRS-M subscale of Expressiveness, TD Twin of ASD (M=3.80, SD=2.35) had marginally worse PRS than TD Twin of TD (M=2.10, SD=1.20) (p=.086), but did not differ from ASD Twin of ASD (M=4.20, SD=1.75).
TD twins of children with ASD were impaired in Expressiveness, but not in overall pragmatic language or other subscales. The Expressiveness sub-domain of the PRS-M includes items such as facial expressions, discussing and empathizing emotions, and reference to unfamiliar objects with sufficient explanation. To extend our results, we will be including siblings (non-twins) to examine the shared environment effect of having a sibling who is the same versus different in age.