Hereditary C2 deficiency: diagnosis and HLA gene complex associations.

Nine families with genetically controlled C2 deficiency have been described where the propositii and family members are heterozygous C2 deficient. The diagnosis of hereditary C2 heterozygous deficiency was suspected on the basis of analysis for CH50, C2 protein, and C2 function, and then confirmed by family studies. Analysis of HLA antigens in these families supported the close association of C2 defiency and HLA-A10 and/or B18, particularly the latter. Analysis by MLC studies revealed recombination in one family between the HLA and B and D loci and in another family probable recombination between the D and C2 complement loci. Therefore, the order of the loci on the sixth chromosome is likely to be C2 complement, HLA-D, HLA-B, HLA-A.