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A B S T R A C T Using isoelectric focusing in polyacrylamide gel and a hemolytic assay for development of patterns, extensive structural polymorphism in human C8 has been delineated. Two C8 allotypes have been determined for two previously studied familes, each with a homozygous C8-deficient propositus. This study suggests that C8 deficiency is a silent or null allele of the C8 structural locus, and that half normal levels of C8 cannot be used as a single criterion for the establishment of heterozygous C8 deficiency. C8 allotypes, as well as 18 other autosomal markers, were also determined for 24 familes. The C8 structural locus is not closely linked to these markers, including the human histocompatibility loci complex.

A slowly progressive autosomal dominant neuromuscular disease--termed spheroid body myopathy--is described in four successive generations and documented by muscle biopsies in five patients of two generations. With an onset in adolescence, the disease proceeds to some motor incapacitation, but life span is apparently not shortened. The salient morphologic feature is the presence of spheroid bodies, chiefly occurring in type 1 myofibers. Ultrastructurally, these spheroid bodies are composed of tiny filaments but are devoid of organelles; in some cases they resemble cytoplasmic bodies. "Smearing in the 1-band" is a frequent and early finding. At a later age, signs of denervation are also present, both clinically and in muscle biopsies. The clinical and morphologic features justify the designation of this neuromuscular condition as a distinct entity.