A 9-year-old boy with severe motor and intellectual disabilities and prolonged abdominal distension.

The patient is a 9-year-old boy with severe intellectual disability and cerebral palsy (Schinzel-Giedion syndrome). Nissen fundoplication and gastrostomy were performed 7 years ago, and an alpha-glucosidase inhibitor (miglitol) was administered due to dumping syndrome. Recently, he presented with abdominal distension and intermittent bloody stool for 9 months. Abdominal radiography revealed gaseous distension with a diffuse frothy pattern (Fig. 1). What is the most likely diagnosis (answer on page 363)?