Mucocele formation is the most common gallbladder disease in dogs. The disease targets purebred dogs resulting in accumulation of thick and dehydrated mucus in the gallbladder which leads to biliary tract obstruction or rupture. Even with surgery to remove the gallbladder, 17% of dogs do not survive. Our long-term goal is to determine the cause of mucocele formation so that we can put an end to suffering and lost lives of these dogs. Our objective here is to gather convincing evidence in support of a hypothesis that mucocele formation is caused by exposure of the gallbladder (via bile) to an environmental contaminant that injures the gallbladder neuronal network in genetically predisposed dogs. Our first aim will be to identify the genetic factors that confer disease risk by performing a genome-wide association study focusing on the breed at greatest risk in the U.S. – the Shetland sheepdog. Our second aim will use untargeted mass spectrometry to identify environmental contaminants residing in gallbladder tissue of dogs with mucocele formation and that distinguish them from dogs that do not form a mucocele. In our third aim we will perform 3-dimensional quantitative imaging of the gallbladder neuronal network to determine if injury is an early feature of mucocele formation. Completion of these aims will 1) locate genes and genomic regions conferring risk to mucocele formation, 2) identify toxicological compounds ostensibly capable of causing mucocele formation, and 3) determine if the gallbladder neural network is the target (and a focus for treatment) of this disease.