Grammatical SLI: A distinct subtype of developmental language impairment?

Grammatical specific language impairment (G-SLI) has been proposed as a distinct subtype of language impairment. We assessed a large sample of twins between 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 presence of language impairment (LI) in one or both twins and 104 twin pairs from 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 positive on four of the five markers. Most children who made grammatical errors 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. Deficits in the use and understanding of grammar are a hallmark of specific language impairment (SLI). Most research on grammatical problems has concentrated on expressive difficulties with grammatical morphology (see Leonard, 1998). However, in at least a subset of children, the ability to understand the meaning signaled by grammatical devices such as inflectional endings or word order is also impaired (Adams, 1990; Bishop, 1979, 1982). In a series of papers, Van der Lely and colleagues (Van der Lely, 1994, 1996; Van der Lely & Stollwerck, 1997) have argued that there is a homogeneous subtype of grammatical SLI (G-SLI), which is characterized by a “representational deficit for dependent relationships” (RDDR) in the computational syntactic system. This leads to inconsistency in forming or using syntactic structures that involve dependent rela 2000 Cambridge University Press 0142-7164/00 $9.50 Applied Psycholinguistics 21:2 160 Bishop et al.: Grammatical SLI tionships between syntactic elements, so that an affected child will rely on other, nonsyntactic cues to interpret meaning in sentences. It is argued that, on comprehension tests that require computation of dependent relationships, children with G-SLI make distinctive errors, which cannot simply be attributed to immature language development. Another claim made by Van der Lely and Stollwerck (1996) is that the etiology of G-SLI is strongly genetic, possibly controlled by an autosomal dominant gene. This is not to imply that all grammar is controlled by a single gene, but rather that a genetic deficit can have an impact on specific mechanisms or representations underlying grammar.