Case Report: Hereditary angioedema masquerading as gastroenteritis.

Hereditary angioedema with C1-inhibitor deficiency (HAE-C1INH) is a rare bradykinin-mediated disorder that may present predominantly with gastrointestinal symptoms, leading to diagnostic delay and unnecessary interventions. We report a 26-year-old man with recurrent abdominal pain, watery diarrhea, bowel wall edema, and transient ascites since 2022, repeatedly misdiagnosed as infectious gastroenteritis. He also reported recurrent hand and foot swelling. Complement testing showed low C4 and reduced C1-inhibitor function, and repeat testing confirmed low C1-inhibitor antigen and function, supporting type 1 HAE-C1INH. During follow-up, genetic testing identified a heterozygous likely pathogenic nonsense variant in SERPING1, NM_000062.3:c.1480C>T (p.Arg494Ter/R494*). Family investigation of 50 relatives identified 13 clinically suspected affected individuals, including three who reportedly died from laryngeal edema; laboratory confirmation was available for the proband and two relatives. This case emphasizes that recurrent, self-limited abdominal attacks with transient ascites should prompt C4 and C1-inhibitor testing and family counseling.