The focus of this section is on the discovery and functional analysis of genes involved in the development and operation of the nervous system. Our broad goal is to define how a network of genes acts to bring about a cellular process. Current research focuses on unraveling the genetics of a complex trait, namely epilepsy. As an entry point for defining genetic interactions, we are specifically mutagenizing in mice the gene for GAD, the biosynthetic enzyme of the neurotransmitter GABA. A construct containing an altered GAD gene has been electroporated into embryonic stem cells, and antibiotic resistant clones have been isolated and screened for the presence of an inactivated GAD gene. These experiments should help determine the role of GAD in neuronal communication, as well as enable us to map additional genes that might act in concert with GAD, and determine whether GAD is involved in disorders characterized by disturbed interneuronal signaling. The transgenic knock-out studies in mice are being complemented by genetic approaches to directly define genes involved with epilepsy in man. One large family with an autosomal dominant pattern of inheritance of epilepsy has been evaluated at the clinical center, under the direction of Dr. W. Theodore. Samples are currently being collected for linkage analysis. When a high degree of linkage is apparent, the region of interest will be subjected to a series of physical and functional tests in order to finally close in on and sequence the affected gene. Positional cloning will also be carried out on additional families with idiopathic epilepsy to identify other genes of the complex network that, when malfunctioning, yields an epileptic phenotype. Knowledge of which gene(s) are affected in various inherited epilepsies, in conjunction with the identification of genes that affect an epileptic phenotype in transgenic mice, will provide insight as to the molecular basis for interneuronal signaling.