EARLY SOCIAL-COMMUNICATIVE AND COGNITIVE DEVELOPMENT OF YOUNGER SIBLINGS OF CHILDREN WITH AUTISM SPECTRUM DISORDERS

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Stone WL, McMahon CR, Yoder PJ, Walden TA Arch Pediatr Adolesc Med. 2007;161:384-390

Summary This study was a prospective evaluation of the developmental abilities of siblings of children with autism spectrum disorders (ASDs). The authors note that relatives of children with ASDs are at a higher risk of having "mild" impairments (not at ASD-threshold diagnosis) in some of the components of the ASD diagnostic criteria, including language delays or impairments in social interactions.

The authors sought to compare a group of young children who had older siblings with ASDs vs younger siblings of "typically developing" (TD) children in an effort to better establish whether the siblings of ASD children are at increased risk for developmental problems.

Over a 3-year period, the investigators at one academic medical center enrolled 64 siblings of ASD children and 42 siblings of TD children.

The subjects were all 12-23 months old, had no severe medical or developmental diagnoses, and came from English-speaking households.

The siblings of TD children could have no family members with developmental disorders and no family history of ASDs or mental retardation in first-degree relatives. The 2 groups were equal demographically (mean age approximately 16 months, 57% male, 87% white) with the exception that mothers of the TD sibling subjects were more likely to have at least a college degree (88% vs 62%).

The 2 groups had approximately the same number of siblings: approximately 1.7 siblings per subject. All subjects underwent evaluation by the investigators who assessed outcomes in multiple domains, including scales of early learning, communication development, sociability, and measures of autism symptoms.

The siblings of ASD children scored lower than the siblings of TD children on several of the measures, including the scales measuring early learning and the scales measuring autism symptoms. They also had lower scores on measures of social-communicative performance. The group differences were not driven by a few severely affected patients in the ASD siblings, with 54% of ASD siblings vs 29% of TD siblings performing below average in 1 or more domains of the early learning battery. Parental assessment (by semi-structured interview) of the subjects revealed that siblings of ASD were more likely to display impaired social behaviors before 2 years old. Again, large proportions of the ASD siblings performed lower in the parental assessment measures, such as 30% of siblings of ASD children understanding fewer than 10 phrases compared with only 2% of siblings of TD children.

The large proportions affected suggested that the deficiencies associated with having an ASD sibling are reasonably common or widespread. In a similar manner, subjects with an ASD sibling used fewer gestures and were more likely to exhibit joint attention deficits. The authors suggest that the lower overall performance of the siblings of ASD children supports the theory of a broad autism phenotype, and they emphasize the careful developmental screening of siblings of children with autism and autism spectrum disorders.

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I suspect that most providers are attentive to developmental screening of siblings of autistic children. However, this study certainly emphasizes the need to be so careful. The study cannot answer a very interesting question as to what is at work here: Are the deficits exhibited by the siblings of autistic children due to innate factors (or limitations); are they the result of exposure to an older sibling with autism; are they the result of exposure to parents with "mild" forms of ASDs; or are these findings due to a combination of all 3 issues? In any case, the broad developmental assessment that these children completed and the pattern of impairment across multiple measures of development suggest that we should all pay very close attention to these at-risk siblings.

Abstract

William T. Basco, Jr, MD, FAAP, Pediatrician, Charleston, South Carolina

Disclosure: William T. Basco, Jr, MD, FAAP, has disclosed no relevant financial relationships.

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