Hypomorphic variant of C3, arthritis, and chronic glomerulonephritis.

Decreased synthesis (hypomorphism) of the fast variant of the third component of complement was detected in three generations of a family in which the propositus has an immune complex-type glomerulonephritis, arthritis, and a false positive test for syphilis. An affected sibling has bursitis, hematuria, and proteinuria. Decreased serum C3 protein was detected in three of four and decreased C3H50 in four of four family members with this hypomorphic variant (C3f). This is the first association between C3f and immune complex-type disease.