The Impact of Birth Order and Sibling Age on Language in Individuals with ASD
Impaired communication is one of the core features of autism. In typical development, siblings can positively influence language development and outcomes (e.g., Hoff-Ginsberg, 1998, Bernicot & Roux, 1998) though birth order plays a role in the nature and size of these effects. Although children with ASD participate in fewer prosocial interactions with their siblings compared to children with down syndrome (Knott et al., 2007) the presence of a sibling in the home may still impact their development. Siblings provide in-home opportunities for practice socializing with peers, but they also introduce competition for parent attention.
This study combines data collected from the University of Washington Twin Study and the Simons Simplex Collection to explore the impact of a typically developing sibling on language and communication in individuals with autism.
First, we matched the ASD affected individual (e.g., proband) from 14 disconcordant twin pairs and 37 disconcordant sibling pairs on age and gender. Probands were between 4 and 17 years (M = 10.3, SD = 3.23). Next, groups were divided based on the age difference between the proband and sibling: (1) proband younger than TD sib by ≥2.5 years (N = 16); (2) probands younger than TD sib by <2.5 years (N = 18); (3) twins (N = 14); (4) proband older than TD sib <2.5 years (N = 21); (5) probands older than TD sib by ≥2.5 years (N = 14). Analyses included scores from the ADOS, ADI, IQ and Vineland for the proband and Vineland for the Sib.
ASD individuals with a twin or a younger sibling have marginally higher verbal IQ scores compared to ASD individuals with an older sibling (<2.5 years) (ps < .08). Probands with a much older sibling (≥2.5 years) have significantly better communication scores on the ADOS compared to those with a sibling <2.5 years older (p = .002) and marginally better scores than those with a sibling <2.5 years younger (p = .09). ASD individuals with a much younger sibling (≥2.5 years) have significantly better ADOS communication scores than those with a sibling <2.5 years younger (p = .02).
Children with ASD who have a twin or younger sibling have higher verbal IQ compared to those with older siblings. For communication scores on the ADOS (which includes items such as stereotyped language and conversation skills), individuals with ASD who were most dissimilar in age to their sib were less impaired than those whose sibling was closer to their own age. Taken together, these findings suggest that birth order and sibling spacing in “simplex” families impact social and communication abilities in children with ASD. Analyses will also be presented on adaptive skills in the probands and sibling.