Postgrad Med J 77:128 doi:10.1136/pmj.77.904.128
  • Self assessment answers

Recurrent abdominal pain—the forgotten cause

C1 INH deficiency:

Q1: Is always associated with peripheral angio-oedema and urticaria


C1 INH deficiency is not associated with urticaria but the angio-oedema may be preceded by a serpiginous erythematous rash which is non-pruritic. Peripheral angio-oedema is a well recognised presentation but mucosal angio-oedema can be life threatening and may involve the bowel.

Q2: Symptoms can be precipitated by the oral contraceptive pill


The oral contraceptive pill and menstrual cycle have been linked to exacerbations of the condition but the most commonly reported precipitating factors are trauma, dental extraction, and emotional stress.1

Q3: Is the most commonly described genetic defect of the complement system and is characterised by a reduction in complement proteins C3 and C4


It is the most commonly described genetic defect of the complement system2 in which C4 and C2 are reduced due to the unchecked activity of C1, but C3 is invariably normal. This is because C3 convertase is not generated due to C4b and C2b being rapidly inactivated in the plasma.

Q4: Is inherited in an autosomal recessive manner and usually presents in the first decade of life


C1 INH deficiency may be inherited in an autosomal dominant (chromosome 11, p11.2–q13 ), manner where it usually appears early in life, or acquired presenting in the …

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