The Dra-/- mouse is the only mouse model for intestinal transporter deficiency that develops substantial diarrhea and serum electrolyte imbalances [17], whereas NHE2-/-, NHE3-/-, cHKA-/-, Aqp4-/- and Aqp8-/- mice have subtle, if any, changes in stool water content and normal serum levels of chloride and sodium [24-29]. Here, AQP8 is linked to hyperinsulinemic hypoglycemia, familial, 4.