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.

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.

18 years of age or younger experiencing chronic, idiopathic diarrhea or abdominal pain for at least 4 weeks.