Congenital Sucrase-Isomaltase Deficiency (CSID) Genetic Prevalence Study (GPS)

Inclusion Criteria: * Must be 18 years of age or younger. * A primary clinical diagnosis of chronic idiopathic diarrhea or chronic abdominal pain for at least 4 weeks. * English or Spanish speaking subjects and parent(s)/guardian only. * Parental consent from one parent/guardian and also subject assent when appropriate based on individual IRB requirements. Exclusion Criteria: * Any condition(s) or finding(s) that in the opinion of the principal investigator suggests an alternative diagnosis for his/her gastrointestinal symptoms. * Abdominal pain primarily related to constipation. * Suspected gastrointestinal infectious disease. * No current use of sacrosidase (Sucraid® Oral Solution). * Known gastrointestinal disease such as celiac disease. * Prior consumption of an investigational medication within the last 4 weeks. * Antibiotics in the last 2 weeks, and no history of viral gastroenteritis within that same period of time. * Known Hepatitis B or C infection (positive HBsAg or HCV within 6 months of enrollment) or Subject-Pugh Class C liver disease of any cause, HIV infection, tuberculosis, Clostridia difficile co-infection, cancer or systemic infections. * Severe neurologic impairment that would prevent them from reporting a history of abdominal pain. * Receiving or received biologic therapies (including infliximab, adalimumab, natalizumab) within 3 months prior to or at enrollment. * Present or past use of immune modulators therapy (e.g., azathioprine, 6MP, methotrexate). * Planned or previous abdominal surgery (e.g., bowel resection). * Subjects with severe, uncontrolled systemic diseases. * Presence of clinical alarm signs, including hypotension, anemia requiring blood transfusions, altered mental status, or inability to tolerate food and/or fluids by mouth.