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.