No major effect of twinning on autistic traits.
Twin status does not inflate autism screening scores.
01Research in Context
What this study did
Cowie et al. (2011) asked a simple question. Do twins show more autism traits than single-born kids?
They gave the CAST screening survey to thousands of UK families. The survey flags kids who might have autism.
What they found
Twin kids scored the same as single-born kids. In fact, twins were slightly less likely to screen positive.
Being a twin did not raise autism trait scores at all.
How this fits with other research
Dworzynski et al. (2009) used the same UK twin registry. They mapped how autism symptoms cluster. Their work set the stage for asking twin-specific questions.
Murphy et al. (2014) later showed extreme autism traits are highly heritable in twins. They trusted the null twin effect, so they could focus on genes rather than twin status.
Torrico et al. (2017) also found null results. Their large European study wiped out earlier gene “hits” for autism. Like Sarah et al., big samples washed away small, shaky claims.
Why it matters
You can stop worrying that twins will always score higher on autism screens. If a twin screens high, look at other causes, not the fact they are a twin. Use the same cut-off and follow-up steps you use for any child.
Want CEUs on This Topic?
The ABA Clubhouse has 60+ free CEUs — live every Wednesday. Ethics, supervision & clinical topics.
Join Free →Apply standard CAST cut-offs to twins; no extra points needed.
02At a glance
03Original abstract
BACKGROUND: It has been questioned whether the process of twinning might be a risk factor for autism spectrum conditions (ASC) and autistic traits. AIM: We sought to determine whether autistic traits and probable disorder, as measured by the Childhood Autism Spectrum Test (CAST), were more pronounced in twins compared to singletons. SAMPLES: Data were analyzed from two large population-based samples of UK children, twins (n = 5,142 twin pairs, aged 8 years) and singletons (n = 2,805, aged 5-9 years). RESULTS: Distributions of CAST scores in both groups were negatively skewed and scores for twins were more variable than singletons. Mean CAST total scores and standard errors (SE) were not significantly different for twins (5.1; SE 0.04) compared to singletons (4.9; SE 0.08). Moreover, contrary to expectations, the likelihood of scoring above the threshold for possible ASC was significantly lower in the twins than the singletons (OR = 0.69; P = 0.002). Subsidiary analyses of CAST scores according to sex, twin type, and subscale scores representing the subdomains of autism found a few significant differences (P<0.01), but the effect sizes for these differences were small and none exceeded η(2) = 0.005. The explanation for these small differences remains obscure, but the very small effect sizes mean they are of little importance. CONCLUSIONS: Our results do not provide evidence to support twinning as a risk factor in the development of autistic traits.
Autism research : official journal of the International Society for Autism Research, 2011 · doi:10.1002/aur.207