Genetic Sucrase-Isomaltase Deficiency (GSID) is a rare genetic disorder where one lacks the enzymes needed to digest sucrose and maltose due to low or absent levels of the enzymes sucrase and isomaltase. This causes undigested sugars to enter the large intestine, where bacteria ferment them causing gas, diarrhea, abdominal pain and other gastrointestinal issues. GSID symptoms range from mild to severe and include gas, diarrhea, vomiting and weight loss. The condition is diagnosed through tests like endoscopy and breath tests and is treated through a lifelong sucrose-free diet and enzyme replacement therapy.