Background: Specific language impairment has previously solely been documented for children acquiring spoken languages, despite informal reports of deaf children with possible sign language disorder. The paper reports the case of a deaf child exposed to British Sign Language (BSL) from birth, who has significant developmental deficits in the comprehension and production of BSL grammar based on formal assessment and linguistic analyses of his sign communication in comparison with age-matched unimpaired signers.
Results: It is shown that linguistic difficulties with BSL verb morphology underlie the child's poor performance compared with same-age native signers.
Conclusions: The appearance of linguistic impairments in sign and spoken languages in comparable domains supports cross-linguistic and modality free theories of specific language impairment.