Abstract
Specific language impairment (SLI) is diagnosed when a child's language development is deficient for no obvious reason. For many years, there was a tendency to assume that SLI was caused by factors such as poor parenting, subtle brain damage around the time of birth, or transient hearing loss. Subsequently it became clear that these factors were far less important than genes in determining risk for SLI. A quest to find “the gene for SLI” was undertaken, but it soon became apparent that no single cause could account for all cases. Furthermore, although fascinating cases of SLI caused by a single mutation have been discovered, in most children the disorder has a more complex basis, with several genetic and environmental risk factors interacting. The clearest evidence for genetic effects has come from studies that diagnosed SLI using theoretically motivated measures of underlying cognitive deficits rather than conventional clinical criteria.
Highlights
Specific language impairment (SLI) is diagnosed when a child’s language development is deficient for no obvious reason
A typical 7- or 8-year-old child with SLI may talk like a 3-year-old, using simplified speech sounds, with words strung together in short, ungrammatical strings—e.g., ‘‘me go there,’’ rather than ‘‘I went there.’’ SLI is a heterogeneous category, varying in both severity and profile of disorder, but in most cases it is possible to demonstrate problems with both understanding and producing spoken language; for example, the child may have difficulty using toys to act out a sentence such as ‘‘the boy is chased by the dog,’’ showing confusion as to who is doing what to whom
The task reveals deficits in people who appear to have overcome early developmental language difficulties, and so it acts as a good marker of resolved language difficulties. When we used this task in a twin study (Bishop, North, & Donlan, 1996), we found evidence of strong genetic influence on impaired nonword repetition
Summary
University of Oxford, Oxford, England OnlineOpen: This article is available free online at www.blackwell-synergy.com. Fascinating cases of SLI caused by a single mutation have been discovered, in most children the disorder has a more complex basis, with several genetic and environmental risk factors interacting. There are, exceptions to this general rule of speedy and robust language acquisition: Children with specific language impairment (SLI) have major problems in learning to talk, despite showing normal development in all other areas (see Table 1). Language impairment in SLI is puzzling precisely because it occurs in children who are otherwise normally developing, with no hearing problems or physical handicaps that could explain the difficulties. The prevalence of SLI has been estimated at around 7% (Tomblin et al, 1997), this will vary with both the diagnostic criteria and children’s age: Long-term language impairments that persist into adulthood are less common than milder delays in preschoolers, which may resolve with time (Bishop & Adams, 1990)
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