Definition: Phylogenetic duodenitis is a rare genetic disorder characterized by inflammation of the duodenum (small intestine) in children and young adults. It typically presents with abdominal pain, nausea, vomiting, diarrhea, and fever. The cause is usually unknown but can be associated with environmental factors such as exposure to certain types of bacteria or viruses. Treatment may involve antibiotics, supportive care, and lifestyle modifications to manage symptoms.