Evidence for a silent or null gene in hereditary C2 deficiency.

Three generations of a family with hereditary C2 deficiency were studied, Six members heterozygous for C2 deficiency were identified by serum C2 levels that were approximately 50% of normal C2 values and the identity was supported by HLA analysis. All six members with low C2 levels had only a single electrophoretic variant. Two of four children did not have the variant found in the parent from whom they inherited the partial C2 deficiency. It is inferred that the low levels of C2 result from the inheritance of a silent or null gene, C2D allelic with the structural genes controlling the electrophoretic variants.