Congenital sucrose-isomaltase deficiency (CSID) is a rare, genetic disease in which mutations in the sucrose-isomaltase (SI) gene cause digestion problems of sucrose resulting in diarrhea and abdominal pain. Children with chronic, idiopathic diarrhea or abdominal pain will have their sucrose-isomaltase gene assessed for a panel of known CSID mutations to determine the prevalence of these mutations in an enriched population and also determine functional deficiency using a breath test.