Low copy numbers of complement C4 and homozygous deficiency of C4A may predispose to severe disease and earlier disease onset in patients with systemic lupus erythematosus

Objectives Low copy numbers and deletion of complement C4 genes are potent risk factors for systemic lupus erythematosus (SLE). However, it is not known whether this genetic association affects the clinical outcome. We investigated C4 copy number variation and its relationship to clinical and serological features in a Northern European lupus cohort. Methods We genotyped the C4 gene locus using polymerase chain reaction (PCR)-based TaqMan assays...