Pediatric systemic lupus erythematosus with C1q deficiency.

Hereditary deficiency of each component of the classical pathway is associated with increased susceptibility to lupus erythematosus (LE). Both the severity of the disease and the strength of this association are greatest for homozygous C1q deficiency, which is extremely rare. In fact, more than 90% of all individuals with deficiency of this component have LE. We report a 3-year-old female infant with history of discoid LE treated with topical corticosteroids for 1 year. She was referred to pediatric department for an exacerbation and extension of cutaneous lesions toward front-arm, hands, legs and feet, a glomerulonephritis, and thrombopenia. Immunologic tests revealed a positive speckled antinuclear antibody at 1/1600 with positive anti-Sm, anti-SSA, and anti-RNP antibodies. Test for anti-DNA was negative. These findings were compatible with a transition to a systemic form of lupus. Systemic corticosteroid treatment was started; however, the patient died by a severe digestive hemorrhage. Hemolytic complement activity (CH50) was undetectable in serum despite normal levels of C3 and C4 suggesting a deficiency of an early component of the complement cascade. Measurement of hemolytic assay for C1 functional activity was less than 1%. C1q deficiency was confirmed by a double immunodiffusion and ELISA using sheep polyclonal anti-C1q antibodies. C1q deficiency is a rare genetic disorder. Thirty-eight of the 41 patients reported to date have developed systemic LE. C1q deficiency may cause systemic LE via a critical role of this component in the physiological clearance of apoptotic cells.