Complement deficiency in pediatric-onset systemic lupus erythematosus

Pediatric-onset systemic lupus erythematosus (pSLE) accounts for about 10%-20% of all patients with SLE. Deficiencies in early complement components of the classical pathway are the strong genetic risk factor for the development of SLE. In this study, clinical and laboratory manifestations of both complement-deficient and normal complement pSLE patients were compared.

To investigate clinical and immunological manifestations of pSLE in Iran, 36 consecutive pSLE patients (onset before 18 years) who were followed up over a period of 2 years, were studied. Complement C1q and C2 levels were measured using radial immunodifusion assay and complement C3 and C4 levels were measured using nephelometry. Medical records were retrospectively evaluated from patient database of Children Medical Center Hospital. Data were assessed through descriptive analysis (confidence interval = 95%), paired t-test, and Pearson correlation test.

Twenty-one patients (58%) had at least one component of complement deficiency. Ten patients (27%) had low C1q level, 11 patients (30.5%) had low C2, nine patients (25%) had low C3, and four patients (11%) had low C4 level. Serum level of complement in pSLE was significantly lower than the control group, except C4 (P = 0.005). The low C1q patients had an earlier age of onset of disease (P < 0.0001). The cutaneous manifestations were more frequent and much more severe in pSLE with low complement (100% vs. 73%). The frequency of renal and musculoskeletal symptoms was equal, but renal morbidity was more common in pSLE with low complement. Positivity for anti-ds-DNA was less common in pSLE with low complement (71% vs. 86%).

In pSLE patients with early disease onset and more aggressive SLE manifestations and negative anti-ds-DNA test, complement deficiency should be considered.