Meningococcal disease in congenital absence of the fifth component of complement.

We describe a family in which 2 brothers had meningococcal infection, 1 of them twice. Their parents were first degree cousins. The brothers showed a complete, isolated deficiency of C5, both antigenic and functional. The parents had half-normal values, and the data are compatible with an inherited C5 deficiency where the defect is transmitted as an autosomal codominant trait.