J . C. is a 3-month-old boy who presents to the pediatric GI clinic for evaluation of chronic diarrhea. J. C. was prenatally diagnosed with Trisomy 21 and an atrioventricular septal defect. He was born at 38 weeks of gestation. After birth, he remained hospitalized for poor oral feeding. He underwent a percutaneous endoscopic gastrostomy (PEG) placement at 3.5 weeks old. He was discharged home shortly after PEG placement. At the time of discharge, his weight was 3.185 kg. He was discharged home on maternal breast milk or Enfamil 20 kcal/oz 60 ml over 30 minutes every 3 hours through the gastrostomy tube. Soon after discharge, J. C. developed emesis and poor weight gain. He was transitioned from maternal breast milk and Enfamil to Enfamil Gentlease. Initially, he had improvement in his Gastrointestinal (GI) symptoms after he was transitioned to Gentlease. Unfortunately, his vomiting worsened, and he began losing weight. He was referred back to pediatric gastroenterology by his pediatrician for evaluation of his vomiting and poor weight gain. On presentation, his weight was 3.16 kg (down 25 g from his discharge weight 8 weeks earlier).On examination: His vital signs were as follows: pulse, 150; temperature, 36.4; respiratory rate, 30; weight, 3.16 kg; and length, 52 cm.Abdomen: Normoactive bowel sounds, nondistended, nontender, PEG in place with moderate erythema. During the clinic visit, he was started on oral and topical antibiotics to treat cellulitis at his G-tube site. He was started on zantac for presumed reflux. The caloric density of his feeds was increased to 24 kcal/oz to help with his weight loss.J. C. continued to have vomiting that seemed to worsen despite the previous interventions. He developed several episodes of diarrhea. His diarrhea was yellow and creamy in appearance. He was having diarrhea up to 10 times per day. He was admitted to a general pediatric service to work up his vomiting, diarrhea, and poor weight gain. While in the hospital, he had multiple interventions. He was started on Imodium but continued to have significant diarrhea with both bolus and continuous feeds. His oral feeds and gtube feeds were stopped and he was started on TPN. An abdominal Computed Tomography (CT) scan and a barium enema were obtained.