RT Journal Article SR Electronic T1 Acquired complement C1 esterase inhibitor deficiency in a patient with a rare SERPING1 variant with unknown significance JF BMJ Case Reports JO BMJ Case Reports FD BMJ Publishing Group Ltd SP e231122 DO 10.1136/bcr-2019-231122 VO 12 IS 9 A1 Eva Rye Rasmussen A1 Kasper Aanæs A1 Marianne Antonius Jakobsen A1 Anette Bygum YR 2019 UL http://casereports.bmj.com/content/12/9/e231122.abstract AB Angioedema (AE) is caused by a wide range of diseases and pharmaceuticals; it can become life-threatening when located to the airways. Patients with deficiency or malfunction of complement C1 esterase inhibitor (hereditary or acquired) experience recurrent AE due to an accumulation of the vasoactive mediator bradykinin (BK). Complement C1 inhibitor normally decreases BK production, so a reduced function hereof causes increased levels. The diagnosis of hereditary or acquired AE can be difficult due to similarities to allergic reactions (swelling, abdominal pain, rash). We describe a 35-year-old man presenting with upper-airway AE progressing rapidly and promptly required cricothyroidotomy. Complement and autoantibody screening together with sequencing of SERPING1 were performed and gave the diagnosis of acquired complement C1 esterase inhibitor deficiency. The patient is unusual to have this disease before the age of 40 years. No associated comorbidities were found. It is important to know that antiallergic medication is not effective in BK-mediated AE.