The Modified Checklist for Autism in Toddlers (M-CHAT) sibling study: Are younger siblings representative of the general ASD population?

Date of Completion

January 2007


Psychology, Clinical




Research indicates that younger siblings of children with autism are at higher risk for the development of autism and other developmental disorders (Silverman, 2001). As a result, many researchers have focused on younger siblings as a way of studying the emergence of autism prospectively. While this research has yielded many interesting findings, it is not known whether siblings are representative of singleton cases of autism spectrum disorders (ASD).^ The current study used the M-CHAT (Robins, et al., 2001), a parent-report checklist, to detect ASD in 16–30 month old younger siblings of ASD probands. Three cohorts of children were compared: multiplex/younger siblings, an early intervention/high-risk singleton sample (EI), and a pediatrician screened/low-risk singleton sample (Peds). Two hundred and thirteen younger siblings, 583 EI toddlers, and 4281 Peds toddlers have been screened, with a mean age of 20 months for each group. Ninety-six younger siblings failed the screening and 78 of these also failed the telephone interview follow-up, and qualified for a developmental evaluation (mean age 23 months). Forty-eight of these siblings have been diagnosed with ASD, suggesting a recurrence rate of 22.5% in our sibling sample, with an ASD recurrence rate of 25% in our University of Connecticut sample and 21% in our University of Washington Sample. ^ With regards to severity of autism, our ASD sibling sample was similar to our singleton ASD sample on all diagnostic variables. However, our ASD sibling sample was higher functioning than our singleton ASD sample in adaptive skills (Vineland Socialization) and cognitive development (Mullen Visual Reception, Fine Motor, and Expressive Language). Although ascertainment bias may play a role in these differences, the data suggest that autism in multiplex families may be different from autism in singleton families and that caution is warranted when generalizing from development of affected younger siblings to development of autism in general. ^