For a 3-month-old boy with diarrhea and no increase in serum glucose after oral glucose, what deficiency is likely present?

• A. GLUT-4
• B. SGLT-1
• C. GLUT-5
• D. Sucrose-isomaltase

Answer: (B)

In this scenario, the boy is exhibiting diarrhea and a failure to increase serum glucose levels after oral glucose administration. The underlying cause for this would most likely be related to a deficiency in the transport mechanisms responsible for glucose absorption in the intestines.

SGLT-1 (Sodium-Glucose Linked Transporter 1) is essential for the absorption of glucose and galactose from the intestinal lumen into the enterocytes. This transporter uses the sodium gradient to facilitate the uptake of glucose, and its deficiency would result in impaired glucose absorption. When a patient with SGLT-1 deficiency consumes glucose orally, the expected response of serum glucose levels rising does not occur, which aligns perfectly with the scenario presented.

Diarrhea is often seen in cases of malabsorption syndromes, like that caused by SGLT-1 deficiency, because unabsorbed glucose in the intestinal lumen leads to osmotic diarrhea. This further supports the diagnosis since the inability to absorb glucose results in excess fluid remaining in the gastrointestinal tract, causing diarrhea.

Therefore, the clinical presentation of diarrhea accompanied by no increase in serum glucose level post oral glucose administration strongly suggests a problem with SGLT-1, confirming that this transporter is likely deficient in the case of the