The serums of patients with hypocomplementemic glomerulonephritis contain a substance that combines with a normal serum cofactor in the presence of magnesium ion to specifically cleave the third component of complement. This lysis of C'3 is 80 to 90 percent complete in 20 minutes at 37 degrees C and pH 7. Neither the nephritic factor nor its cofactor is identifiable with the complement system.

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Hyperkalemic periodic paralysis (hyperKPP) and paramyotonia congenita (PC) are genetic muscle disorders sharing the common features of myotonia and episodic weakness. In hyperKPP, patient symptoms and signs are worsened by elevated serum potassium, whereas in PC, muscle cooling exacerbates the condition. There are patients in whom features of both hyperKPP and PC are present. These diseases result from molecular alterations in the adult skeletal muscle sodium channel. This report summarizes our sodium channel mutation analysis in 25 families with hyperKPP and PC. We also report the putative disease-causing mutation in acetazolamide-responsive myotonia congenita, a related disease in which myotonia is worsened by potassium but in which episodic weakness does not occur. This missense mutation (I1160V) occurs at a very highly conserved position in the sodium channel, cosegregates with the disease, and was not present in any of a large panel of normal DNAs. Electrophysiologic characterization of specific mutations will lead to better understanding of the biophysics of this voltage-gated ion channel.

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All immune origin of glomerulonephritis, with complement playing a major role, was first suspected 50 yr ago when it was found that serum complement levels in nephritis were often low. Only recently however, with the identification of individual components, have details of the complement reaction become susceptible to investigation. It is already apparent that there are differences in the way in which complement is involved in nephritis. For example, serum levels of individual components have been shown to be variably reduced depending upon the type of nephritis (1-3). Furthermore, deposition of C3 in the glomeruli occurs in many cases in which C3 and total complement levels have remained normal during the course of the disease (4-6). In other types of nephritis, however, the configuration of C3 deposition correlates well with the supposed target of the immune reaction (4, 5).The participation of complement in producing the type of nephritis designated hypocomplementemic persistent or membranoproliferative is of special interest. In this disease CHs0 and C3 may remain at very low levels over long periods (6, 7) and C3 is usually found in the glomerular capillary walls by immunofluorescent techniques, often without the presence of identifiable IgG. 1 The persistently reduced serum levels of C3 have been explained by some as the result of diminished synthesis of C3 (8) and ascribed by others to an ongoing complement reaction in the glomeruli in which C3 is continuously being broken down (9). Recent observations suggest that a site of complement breakdown may be circulating plasma. Inactivators of guinea pig (10) and human (11) complement have been found in the serum of patients with acute, chronic hypocomplementemic, and lupus nephritis, and in a previous communication from this ]nboratory, Spitzer et al. (12) reported the presence of a factor in the