From MedlinePlus Genetics
Glucose-galactose malabsorption is a condition in which the body cannot take in (absorb) the sugars glucose and galactose, which primarily results in severe diarrhea. Beginning in infancy, severe diarrhea results in weight loss and dehydration that can be life-threatening. Small amounts of the simple sugar glucose in the urine (mild glucosuria) may occur in this disorder. Rarely, affected infants develop kidney stones due to deposits of calcium in the kidneys (nephrocalcinosis).

The signs and symptoms of glucose-galactose malabsorption appear early in life when affected infants are fed breast milk or regular infant formulas. These foods contain glucose, galactose, and another sugar called lactose that gets broken down into these two sugars. When these sugar-containing foods are ingested by affected individuals, it leads to diarrhea and other health problems. If foods that contain glucose, galactose, and lactose are removed from the diet, the diarrhea stops.  https://medlineplus.gov/genetics/condition/glucose-galactose-malabsorption