A 19-year-old woman has had two episodes of meningococcal meningitis and one episode of disseminated gonococcal infection. Screening for common immunodeficiencies including HIV, immunoglobulin levels, and neutrophil function is normal. The most likely abnormality is:

• A Selective IgG2 subclass deficiency
• B Deficiency of mannose-binding lectin
• C Deficiency of C3 leading to failure of opsonization
• D Deficiency of a terminal complement component (C5 through C8) ✓

Explanation

Terminal complement deficiencies (C5, C6, C7, C8, rarely C9) prevent formation of the membrane attack complex, which is the principal defense against Neisseria species. Affected patients suffer recurrent meningococcal and gonococcal infections despite otherwise intact immunity. C3 deficiency causes severe recurrent pyogenic infections with immune complex disease, a broader phenotype than isolated neisserial susceptibility.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.