The goal of the project is to identify and clone the gene(s) responsible for the Alagille Syndrome (AGS) by a positional cloning approach. The first step towards this goal is to define the smallest genomic candidate region for AGS at 20p12 and to begin to identify genes within this region which are, by definition, candidate genes for the disease. In a collaborative effort with clinician-investigators studying the Alagille syndrome, metaphase chromosomes and genomic DNA from affected individuals will be studied for subchromosomal deletions and for mutations in the candidate genes. Characterization of genes involved in Alagille syndrome could provide important insight into the pathophysiology of the disease, the development of normal liver and treatment of this disease. Recently, we and others found that mutations in Jagged1, a Notch1 receptor are responsible for Alagille Syndrome.