Mutations in the SI gene lead to a defective sucrase-isomaltase enzyme, which impairs its catalytic function. This deficiency means that individuals with CSID cannot effectively break down sucrose and maltose, leading to symptoms such as abdominal pain, bloating, diarrhea, and malnutrition. The lack of effective catalysis results in the accumulation of these sugars in the gut, which can further cause osmotic imbalances and gastrointestinal distress.
