Pediatric systemic lupus erythematosus with C1q deficiency

Area of Science:

• Immunology
• Genetics
• Rheumatology

Background:

• Hereditary deficiencies in the classical complement pathway components are linked to lupus erythematosus (LE).
• Homozygous C1q deficiency presents the strongest association with LE, though it is extremely rare.
• Over 90% of individuals with C1q deficiency develop LE, underscoring its significance.

Observation:

• A 3-year-old female with discoid LE experienced disease exacerbation, including skin lesions, glomerulonephritis, and thrombocytopenia.
• Immunologic tests showed positive antinuclear antibodies (ANA) with anti-Sm, anti-SSA, and anti-RNP, indicative of systemic lupus.
• Hemolytic complement activity (CH50) was undetectable, with normal C3 and C4 levels, suggesting early complement component deficiency.

Findings:

• Functional C1q activity was less than 1%, confirming C1q deficiency.
• C1q deficiency was further validated through immunodiffusion and ELISA assays.
• The patient tragically died from severe digestive hemorrhage despite systemic corticosteroid treatment.

Implications:

• C1q deficiency is a rare genetic disorder strongly associated with systemic lupus erythematosus.
• This case underscores the critical role of C1q in clearing apoptotic cells, a process vital for preventing autoimmunity.
• Understanding C1q's function is crucial for managing and potentially treating lupus erythematosus in patients with this deficiency.