As shown in Figure 1, LI occurs due to the inability of the human body to digest and absorb dietary lactose (“lactose malabsorption”) due to low or absent activity of lactase (“lactase deficiency”) [12,16,17,18], and it is the most common carbohydrate intolerance during childhood [5]. The gene discussed is LCT; the disease is hyperinsulinemic hypoglycemia, familial, 4.