A 2-week-old female infant presents with acute-onset bilious vomiting and severe abdominal pain. On examination, the abdomen is distended and tender. Plain abdominal X-ray shows multiple dilated small bowel loops with air-fluid levels. Upper GI contrast study demonstrates the duodenum and jejunum positioned on the right side of the abdomen, with the cecum in the midline. The radiologist notes that the mesentery appears to be attached to a single narrow pedicle. Emergency laparotomy reveals the small bowel twisted around the superior mesenteric artery. What is the embryological abnormality responsible for this presentation?