Grammatical SLI: A distinct subtype of developmental language impairment?

Grammatical specific language impairment (G-SLI) has been proposed as a dis tinct subtype of language impairment. We assessed a large sample of twins b etween the ages of 7 and 13 years on language comprehension tests sensitive to G-SLI. The sample included 37 same-sex twin pairs selected for the pres ence of language impairment (LI) in one or both twins and 104 twin pairs fr om the general population. The number and patterns of errors in those with LI replicated findings from previous studies of G-SLI. Qualitative markers of G-SLI were derived from the tests. Out of 144 children for whom complete data were available, 2 scored positive on all five markers and 9 scored po sitive on four of the five markers. Most children who made grammatical erro rs characteristic of G-SLI had co-occurring deficits in other areas. These results raise questions for theories that treat this disorder as an all-or- none modular deficit.