The overall goal of the proposed research is to investigate issues pertaining to genetic etiology of specific developmental language impairment (LI), using family research designs. Specifically, we aim to use case-control family research designs to determine whether there is significant family aggregation of processes associated with developmental language impairment amongst the primary relatives (biological parents, siblings) of LI children and, if so, whether the rates and patterns of expression are compatible with any known mode(s) of genetic transmission. A further goal of this research is to investigate whether temporal processing disorder meets the criteria as a biological trait marker, which could be used for classifying family members of LI probands (especially adults) as affected or unaffected in future molecular genetic research. This is a crucial, but currently limiting, step necessary for future gene-linkage studies. Three converging genetic research strategies are proposed: using a case- control family design, 1) to determine whether the primary relatives of LI children differ significantly on a selected battery of speech, language, temporal processing and reading measures from the primary relatives of matched control children; 2) to determine whether speech, language, reading and/or temporal processing disorders aggregate within the families of LI probands, and if so, whether the rates and patterns of expression are compatible with any known mode(s) of genetic transmission; and 3) using data from family studies, determine whether temporal processing disorder may represent a biological trait marker for developmental language disorder.
