DESCRIPTION: This competing continuation proposal aims to extend the current studies of an Extended Optional Infinitive (EOI) period as a grammatical marker of Specific Language Impairment (SLI) in young children. Current cross-sectional and longitudinal studies provide strong support for a grammatical phenotype of SLI characterized by an extended period of acquisition of tense-related grammatical morphemes. New questions arise. Foremost are questions about how long the EOI period persists in affected children, the grammatical symptomology in older children and adolescents, whether or not an EOI grammar is "reset" to the adult grammar or is "compensated" to approximate the adult grammar, and whether an EOI period is an inherited condition. In order to study these questions, the following specific aims are proposed: 1) To extend the current longitudinal study of the morphosyntax of a well-defined clinical sample of young SLI children, first examined when they were preschoolers, to the 9- to 13-year-old range. This would generate descriptive evidence over the period from 2 1/2 years to 13 years, comprising the most detailed and extended picture of morphosyntactic development available to date; 2) To identify grammatical markers for the condition of SLI for children in the elementary-school-age range; and 3) To investigate the genetics of SLI. This objective has three components. 3.1- To investigate the grammatical competence of the nuclear family members of a group of SLI probands first examined as preschoolers and known to have clearly delineated grammatical limitations and competencies. This would constitute the first formal evaluation of a morphosyntactic phenotype. 3.2 -To identify "affected" family members of the probands, and 3.3 -To initiate molecular genetic studies in an exploration of possible genetic contributions to the observed familial affectedness. The research objectives will take advantage of a well documented clinical longitudinal sample, and unaffected controls. The clinical sample is of interest because these children continue to show affectedness at a relatively advanced age, and their families show an elevated rate of affectedness, as compared to control families. A further resource is the development of new experimental probes designed to measure morphosyntactic competence in a theoretically interesting, clinically valid, and efficient manner. The study outcomes will be immediately relevant for clinical methods of identification of affected individuals who are unlikely to "outgrow" early childhood language impairments. The outcomes will contribute advances in our understanding of individual variation in morphosyntactic competencies across the life span, and etiological factors in the condition of SLI.