Symptoms may begin as early as the first day of life or a few days after birth, when the newborn is exposed to lactose from milk. They include severe, chronic diarrhea, dehydration, and failure to thrive. Early recognition and treatment are important. In severe cases, the disorder may become life-threatening.
Among infants, discontinuation of oral feeding may stop the diarrhea but it will start again when oral feeding is reinstated if the child is fed formula containing glucose. The diarrhea can be quite severe and may readily lead to nutritional wasting and severe dehydration.
In some cases, the affected child grows up with chronic but intermittent diarrhea made worse by sugar-rich meals. Modest amounts of sugar in the urine (glucosuria) of an affected child may be a warning that kidney stones are developing.
In adults, symptoms of glucose-galactose malabsorption may include bloating, nausea, diarrhea, abdominal cramps, rumbling sounds caused by gas in the intestine (borborygmi) and excessive urination.