Background: Language abilities of siblings of children with autism were examined to explore the possibility that language abilities are behavioral markers specific to the genetic liability for autism, as part of the broader phenotype.
Method: Language abilities were compared among 27 siblings of children with autism, 23 siblings of children with mental retardation of unknown etiology (MR), and 22 siblings of children with developmental language disorders (DLD). Groups were matched by siblings’ age, gender, birth order, family size, ethnicity, family income and by probands’ gender and mental age.
Results: Siblings of children with autism achieved higher scores than siblings of children with DLD on receptive, expressive, and total language scales of the Children's Evaluation of Language Fundamentals and on verbal IQ. Moreover, within the DLD group, school problems in the domains of reading and arithmetic were more prevalent than within the other two groups. Only 2 siblings of children with autism received clinical diagnoses based on DSM-IV criteria compared to 3 siblings of children with MR and 7 siblings of children with DLD.
Conclusions: After excluding data of the diagnosed siblings, no differences in language abilities could be discerned among the groups, except that more siblings in the DLD group were identified as having language difficulties. In summary, although language deficits characterize autism, siblings of children with autism were not found to demonstrate deficits in language skills assessed by formal language tests, IQ, or academic skills.