Gilbert's synrome, often shortened to the acronym GS, is the most common hereditary cause of increased bilirubin, and is found in up to 5% of the population (though some Gastroenterologists maintain that it is closer to 10%). The main symptom is otherwise harmless jaundice which does not require treatment, caused by elevated levels of unconjugated bilirubin in the bloodstream (hyperbilirubinemia).