To the Editor.
—Inherited deficiencies of late complement components are rare and are associated with an increased susceptibility to a single episode or to recurrent neisserial infections and, less frequently, with autoimmune disease.1 To the best of our knowledge only 19 homozygous C5-deficient patients have been described so far.1-5 We report preliminary data of two further cases of a selective C5 deficiency (C5D) in a Swiss family, each revealed by the occurrence of meningitis (Neisseria meningitidis, group C and B, respectively). In the two subjects, C5 was not detectable by radial immunodiffusion (RID) using monospecific antisera. In both patients, sequential titration of hemolytic complement by sensitized sheep red blood cells revealed levels of only 1% of normal. In contrast, the functional alternative pathway was only partially affected (between 50% and 65% of the normal mean) as titrated by lysis of rabbit erythrocytes at physiologic ionic strength in the