Are specific language impairment and dyslexia distinct disorders?
OBJECTIVE
The purpose of this study was to determine whether specific language impairment (SLI) and dyslexia are distinct developmental disorders.


METHODS
Study 1 investigated the overlap between SLI identified in kindergarten and dyslexia identified in 2nd, 4th, or 8th grades in a representative sample of 527 children. Study 2 examined phonological processing in a subsample of participants, including 21 children with dyslexia only, 43 children with SLI only, 18 children with SLI and dyslexia, and 165 children with typical language/reading development. Measures of phonological awareness and nonword repetition were considered.


RESULTS
Study 1 showed limited but statistically significant overlap between SLI and dyslexia. Study 2 found that children with dyslexia or a combination of dyslexia and SLI performed significantly less well on measures of phonological processing than did children with SLI only and those with typical development. Children with SLI only showed only mild deficits in phonological processing compared with typical children.


CONCLUSIONS
These results support the view that SLI and dyslexia are distinct but potentially comorbid developmental language disorders. A deficit in phonological processing is closely associated with dyslexia but not with SLI when it occurs in the absence of dyslexia.
Catts
Hugh W
HW
Department of Speech-Language-Hearing, University of Kansas, Lawrence 66045, USA. catts@ku.edu
Adlof
Suzanne M
SM
Hogan
Tiffany P
TP
Weismer
Susan Ellis
SE
D000293:Adolescent; D000704:Analysis of Variance; D001184:Articulation Disorders / Q000209:etiology / Q000503:physiopathology; D002648:Child; D002675:Child, Preschool; D003071:Cognition; D003937:Diagnosis, Differential; D004410:Dyslexia / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007361:Intelligence Tests; D007806:Language Disorders / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D007807:Language Tests; D008137:Longitudinal Studies; D008297:Male; D008606:Mental Processes; D010700:Phonetics; D011932:Reading