Duodenum/chemistry; Endothelium, Lymphatic/chemistry; Intestinal Mucosa/chemistry; Intracellular Signaling Peptides and Proteins/analysis; Lymphangiectasis, Intestinal/metabolism; Lymphangiogenesis; Protein-Losing Enteropathies/etiology; Transcription Factors/analysis; Adult; Aged; Case-Control Studies; Duodenoscopy; Duodenum/pathology; Duodenum/physiopathology; Endothelium, Lymphatic/pathology; Endothelium, Lymphatic/physiopathology; Female; Forkhead Transcription Factors/analysis; High Mobility Group Proteins/analysis; Homeodomain Proteins/analysis; Humans; Immunohistochemistry; Intestinal Mucosa/pathology; Intestinal Mucosa/physiopathology; Intracellular Signaling Peptides and Proteins/genetics; Lymphangiectasis, Intestinal/complications; Lymphangiectasis, Intestinal/physiopathology; Male; Middle Aged; Protein-Losing Enteropathies/metabolism; Protein-Losing Enteropathies/physiopathology; RNA, Messenger/analysis; Reverse Transcriptase Polymerase Chain Reaction; SOXF Transcription Factors; Transcription Factors/genetics; Tumor Suppressor Proteins/analysis; Vascular Endothelial Growth Factor C/analysis; Vascular Endothelial Growth Factor D/analysis; Vascular Endothelial Growth Factor Receptor-3/analysis; Vesicular Transport Proteins/analysis