Porphyria cutanea tarda (PCT) is caused by reduced activity of uroporphyrinogen decarboxylase (URO-D) in the liver, yielding hepatic accumulation of uroporphyrins and photosensitive skin lesions. Excess hepatic iron, together with inappropriately high iron absorption, also occurs in PCT. A new major histocompatibility complex class I-like gene (HFE, also previously named HLA-H) has been identified, and 2 missense variants were found in 87% of patients with hereditary hemochromatosis 1 (another iron disorder), as well as in PCT patients. 2 We assessed the role of HFE mutations in Spanish PCT patients (sporadic [S] and familial [F]) by an allelic association study between the disease and the 2 described HFE mutations (Cys282Tyr and His63Asp). The Cys282Tyr mutation replaces the normal cysteine residue at position 282 by a tyrosine and disrupts the disulfide bridge present in the โฃ3 domain; the His63Asp mutation replaces a histidine residue at position 63 (โฃ1 domain) by an aspartic acid. Eighty-eight unrelated PCT patients (69 S-PCT and 19 F-PCT; 176 chromosomes in total) were studied. The diagnosis was based on the typical symptoms of photosensitive skin and elevated urinary uroporphyrin levels. Fifty unrelated healthy subjects were used as controls.
Genomic DNA was extracted from blood leukocytes. Polymerase chain reaction (PCR) was used to amplify exons 2 and 4 (encoding the โฃ1 and โฃ3 domains) with primers HEMEx2-5ะ(5ะ-CTT TGG GCT ACG TGG ATG ACC) and HEMEx2-3ะ(5ะ-CTG GCT TGA AAT TCT ACT GGA AAC C) and primers HEMx4-5ะ(5ะ-GGT GTC GGG CCT TGA ACT ACT ACC) and HEMx4-3ะ(5ะ-GGG CTC CCA GAT CAC AAT GAG G), respectively. The point mutation in the โฃ1 encoding region was identified by the loss of a Bcl I site; the point mutation in the โฃ3 encoding region was identified by the gain of an Rsa I site. Digested PCR fragments were analyzed by polyacrylamide gel electrophoresis.
The frequencies of HFE mutations and genotypes of patients and controls are reported in Table 1. The Cys282Tyr mutation was present on 10.8% of chromosomes from S-PCT compared with 2% of control chromosomes. The frequency of the His63Asp mutation was also increased in the S-PCT group (32.6%) versus control (16%).
No significant association of any of these mutations was found in the F-PCT group, although the sample size was small. Homozygosity for the His63Asp mutation and compound heterozygosity are the most common genotypes related to the disease (Table 1). The high prevalence of these mutations in the Spanish patients suggests an involvement of the HFE gene in the pathogenesis of S-PCT. It is remarkable that the most frequent HFE mutation found in Spanish patients is His63Asp as in Italians, 2 while northern Europeans or Americans with PCT more commonly exhibit the Cys282Tyr 3,4 mutation. This is reminiscent of other HLAassociated diseases such as insulin-dependent diabetes and rheumatoid arthritis. 5 Thus, for studying HLA-linked diseases, including hemochromatosis and PCT, the patient' s ancestry should be considered.