Co-morbidity of autism and SLI: kinds, kin and complexity

There has been a long-standing interest in the relationship between specific language impairment (SLI) and autism spectrum disorder (ASD). In the last decade Tager-Flusberg and colleagues have proposed that this relationship consists of a partial overlap between the two. Therefore, among children with ASD there exists a subgroup who have SLI and ASD which has been called 'ALI'. Tager-Flusberg's laboratory has presented several papers showing similar language profiles and brain structure abnormalities in both SLI and ALI. Others (Bishop, Whitehouse, Botting, Williams) have been less convinced that these ALI children have both ASD and SLI. Although they generally agree that the two groups are grossly similar, careful inspection of the data shows that there are differences. I will argue that many of the problems in this debate stem from a view of SLI that represents a particular kind of language learner and therefore a particular and unique profile can be assumed. I argue for recognizing that SLI is not likely to be a unique kind of language learner. Many of the features reported to be characteristic of SLI are also found in other forms of neurodevelopmental disorders. Other features are the outgrowth of studying clinically identified children with SLI and thus the profile appears to reflect biases and practices in the clinical service system. As a result it may be more reasonable to conclude that there is a large group of children with ASD who have poor language skills. The question then remains why are there so many children with ASD who also have poor language? There are several factors that collectively are strong candidates for answers to this question.