Analysis of uroporphyrinogen decarboxylase complementary DNAs in sporadic porphyria cutanea tarda.

BACKGROUND

Sporadic porphyria cutanea tarda (S-PCT) has been considered an acquired disease because of the generation of liver-specific inhibitors of uroporphyrinogen decarboxylase (URO-D) activity. Several families have been described with S-PCT in multiple generations, raising the possibility of an inherited basis for the disease. To determine if S-PCT is associated with mutant URO-Ds that might be sensitive to liver-specific inhibitors, a molecular analysis of genomic and hepatocellular URO-Ds was undertaken.

METHODS

Total RNA from lymphoid cell lines from three unrelated patients with S-PCT and poly A+ RNA from liver biopsy samples from two additional patients was used as a template for single-stranded cDNA synthesis, and URO-D sequences were amplified and sequenced. DNA prepared from peripheral blood leukocytes was used as a template to polymerase chain reaction (PCR) amplify the promoter region of the URO-D gene. Sequencing of PCR products was performed completely in both directions by the chain termination method using a variety of custom oligonucleotide primers.

RESULTS

Ten URO-D alleles were sequenced, and no mutations were found. The promoter region of the URO-D gene was also normal.

CONCLUSIONS

It is concluded that S-PCT is not due to mutations at the URO-D locus. If inherited factors are involved, other loci must be affected.