HLA-linked hemochromatosis alleles in sporadic porphyria cutanea tarda.

We tested the hypothesis that the hepatic siderosis that characterizes sporadic porphyria cutanea tarda is due to the presence of HLA-linked hemochromatosis alleles. We studied 21 probands with sporadic porphyria cutanea tarda and 135 of their relatives by determining HLA haplotypes and measuring transferrin saturation and serum ferritin concentration. Liver biopsies were performed in all probands and in relatives when appropriate. Seventeen pedigrees were available and were studied by both likelihood analysis and by a gene counting method. We estimated that 10 of the 17 probands with available living relatives possessed at least one hemochromatosis allele. Thirteen of the 21 probands (62%) possessed at least one HLA-A3 alloantigen. Eighteen of 69 relatives who shared an HLA haplotype with a proband (26%) had an elevation of transferrin saturation or serum ferritin concentration. Only one first-degree relative not sharing an HLA haplotype with a proband had an elevated transferrin saturation or serum ferritin concentration. These findings indicate that HLA-linked hemochromatosis alleles are far more common in patients with sporadic porphyria cutanea tarda than in individuals in the general population and may be responsible for the hepatic siderosis associated with most cases of sporadic porphyria cutanea tarda.