An 11 year old boy starts suffering recurrent angioedema of lower limbs, of pale reddish or whitish color, not associated to urticaria, painful to the touch and causing discomfort when appearing in joints. In several occasions he has experienced palpebral and facial edema, the first times repeating every 30 or 45 days, with no apparent cause. Nearly all cases were treated with steroids and antihistamines in both primary health care and hospital improving in 36 hours with or without treatment. After a 10 month-course of evolution he suffers an episode of edema of tongue, uvula and pharynx and was treated as in other occasions. The outbreaks have increased to 2-3 a month. It was decided to make a dermatological and allergological study after persistence, increased frequency (up to 10 outbreaks in 6 months) and severity of the episodes, allergic diseases and anaphylactic reaction were discarded. This was demonstrated analytically determining immunoglobulin E (IgE) serum within normal levels. As consequence of the findings it was decided to expand the research with the following: Serum total Ig E: 19.80 UI/ml (NR: 150-1,000 UI/mL) Specific allergen Ig E: negative Prick-test with regular neumollergy provocation: negative Food prick-test: negative Latex prick-test: negative Simplex anisakis prick-test: negative ASLO: 184 UI/mL (NR: <200 UI/mL) TSH: 4.6 U/L (NR: 0.5 – 5 U/L) FT4: 1.2 mcg/mL (NR: 0.5 – 1.3 mcg/mL) ANA: negative Proteinogram: Albumin: 4.3g/dl; reference value 3.5-5.3 Alpha-1 globulins: 0.3g/dl; reference value 0.1-0.3 Alpha-2 globulins: 0.6g/dl; reference value 0.4-0.8 Beta-globulins: 0.7g/dl; reference value 0.5-1 Gamma-globulins 1.1g/dl; reference value 0.8-1.6 Albumin/globulin ratio: 1.6 reference value 1.3-2.2 As consequence of the findings it was decided to expand the research with the following: Values found Reference values Complement C3 148.20 mg/dl 90-180 mg/dl Complement C4 0.90 mg/dl 10-40 mg/dl Complement C1q 22.30 mg/dl 10-25 mg/dl C1 Esterase Inhibitor 6.14 mg/dl 22-34 mg/dl Complement C5 19.90 mg/dl 4-15 mg/dl 1. What is the most likely abnormality this child is suffering from? 2. What is the main reason for this disorder? 3. How does this deficiency manifest in the swelling seen in this child? 4. What is one of the major concerns with this disorder? 5. Explain the acquired form of this disorder.