C3 variants and disease.

The distribution of C3 variants in dermatitis herpetiformis, thyroid cancer, spinal muscular atrophy, multiple sclerosis and psoriasis was studied, and also the Bf phenotype distribution in thyroid cancer. In thyroid cancer there was a significant deficit of heterozygotes for the C3 locus, a possible decrease in the C3F allele frequency and a significant elevation of frequency of the BfF allele. The possible involvement of these alleles in susceptibility to thyroid cancer appears worth further examination.