1. Presented by Gabrielle Bailey MD, and reviewed by Mark Marzinke, PhD.

An infant presented to the emergency room for possible seizure activity and was found to be hypoglycemic with a glucose level of 35 mg/dL (reference range: 71-99 mg/dL) due to poor feeding. The infant's care provider also mentioned that they had been having diarrhea with loose stools for several months. The infant was afebrile upon presentation and admitted for further management of hypoglycemia and work-up of the cause of the diarrhea.

To interrogate the etiology of the patient's diarrhea, the clinical team ordered stool electrolytes, stool culture, stool ova and parasites, adenovirus, norovirus, and stool reducing substances. The results are shown below:


The calculated stool osmotic gap was 26 mOsm/kg.

What is the most likely cause of their chronic loose stools?