Hereditary angioedema
A very rare disorder characterized by a defect of the gene (found on chromosome 11) that codes for a protein called C1-inhibitor. In most cases insufficient quantities of the protein are created; a some cases involve adequate quantities of an incorrectly formed protein that does not work properly. Mutations of the gene can cause either problem; since the net result is the same, the distinction is generally academic. The disorder is characterized by swelling of the blood vessels (as the name implies); this is often seen in the face but can happen anywhere. Swelling near or around airways is a life-threatening emergency. Low levels of C1-inhibitor alone are not adequate to diagnose this disorder; some other diseases, such as SLE, are also characterized by this symptom. A laboratory test exists to measure blood levels; it requires collection of a small quantity of venous blood.