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Specific language impairment (SLI) is a developmental language disorder that can affect both expressive and receptive language. SLI is a relatively "pure" language impairment, meaning that is not related to or caused by other developmental disorders, hearing loss or acquired brain injury. Some children with SLI may acquire language in the same sequence as normally-developing children, but at a slower rate. SLI manifests itself in different ways across individuals, but a hallmark of SLI is difficulty with inflected forms of words. For instance, a native speaker of English who had SLI might not always use "-ed" to mark regular past tense forms of verbs.
SLI affects approximately 6% of the population, of which a quarter are severely impaired. Boys are more frequently affected than girls, and SLI often affects both members of monozygotic twins.
In order to classify a disorder as specific language impairment, it is often considered necessary for the verbal IQ to be at least 20 points below the non-verbal IQ. This can cause problems in the diagnosis of SLI when for example studying twins of approximately equal non-verbal intelligence if the verbal intelligence is not substantially worse. 
In some cases, SLI may be inherited. It appears to be related to the FOXP2 gene.
- ^ Gopnik, M. and Goad, H. (1997) "What underlies inflectional error patterns in genetic dysphasia?" in Journal of Neurolinguistics Vol. 10, No. 2-3. pp. 109-137
References & BibliographyEdit
- Hoff, Erika (2005). Language Development (3rd ed.). Belmont: Wadsworth. ISBN 0-534-64170-9.
- Shipley, Kenneth G. & McAfee, Julie G. (2004). Assessment in Speech-Language Pathology: A Resource Manual (3rd ed.). Clifton Park: Thomson. ISBN 1-4018-2751-9.
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