Lack of association between promoter polymorphism of the tumor necrosis factor-alpha gene and psoriatic arthritis in Japanese patients.

The analysis of population-speci®c human leukocyte antigen (HLA) has provided evidence that susceptibility to psoriasis is linked to HLA with racial differences (Henseler, 1997). Tumor necrosis factor-a (TNF-a) gene is also mapped within the HLA region and its product has been reported as one of the most important cytokines in the pathogenesis of psoriasis (Uyemura et al, 1993). Recently, HoÈhler et al (1997) reported in this journal a signi®cant increase of subjects carrying A at position 238 of TNF-a gene promoter region in the psoriatic arthritis (PsA) group, as well as in that of early-onset psoriasis vulgaris (PsV). These ®ndings, however, are still controversial (Jacob et al, 1999; HoÈhler, 1999). Jacob et al (1999) have also shown in the journal that promoter polymorphism at -238 of the TNF-a gene was not associated with early onset PsV when tested by the transmission disequilibrium test. Very recently, it has been demonstrated that an increased frequency of the TNF-238.A (A at -238) allele detected only in male patients but not in female patients with early-onset PsV (Reich et al, 2000). On the other hand, there are only a few reports on whether polymorphism of the TNF-a promoter region and PsA are associated or not, because only a few cases are investigated. Moreover, three new polymorphisms at positions -1031 (T to C change), -863 (C to A), and -857 (C to T) have been identi®ed in the Japanese population (Higuchi et al, 1998). In this study we evaluated the association between promoter polymorphism of the TNF-a gene and PsA in the Japanese population. Twenty Japanese patients (eight females and 12 males) suffering from PsA were studied (the median age was 44 y, ranged from 25 to 70). The control population consisted of 87 locally recruited, unrelated volunteers (21 female and 67 males with a median age of 52 y ranged from 15 to 81). Peripheral blood mononuclear cells were separated by the Ficoll method for isolation of genomic DNA. A 1042 bp DNA fragment of the 5¢ ̄anking region of the TNF-a gene at position -1107 to -66 was ampli®ed by PCR with a sense primer 5¢GCTTGTGTGTGTGTGTCTGG-3¢ and an anti-sense primer 5¢-GGACACACAAGCATCAAGG-3¢ (Higuchi et al, 1998). Polymerase chain reaction (PCR) products were run on ethidium bromide-stained agarose gel, and then excised DNA bands from the gel were puri®ed using a GENECLEAN II kit (BIO 101, La Jolla, CA). These puri®ed PCR products were directly sequenced by the dideoxy nucleotide dye terminator cycle sequencing method using two different primers, 5¢GCTTGTGTGTGTGTGTCTGG-3¢ (Higuchi et al, 1998) for the polymorphism at -1031, -863, and -857, and 5¢TTCCTGCATCCTGTCTGGAA-3¢ (D'Alfonso and Richiardi, 1994) for those at -308 and -238, respectively. As shown in Table I, all patients with PsA studied have a genotype G/G at both -238 and -308, whereas 4.6% (four of 87) and 3.4% (three of 87) of controls have a genotype G/A at -238 and -308, respectively. Gene frequencies for the TNF-238A allele in the Japanese controls were similar to those reported by the authors for West European Caucasians (2.3% vs 3.5%) (HoÈhler et al, 1997) and the previous report for Japanese patients (2.3% vs 2.0%) (Higuchi et al, 1998). The frequencies for the TNF-308A (A at -308) allele in the Japanese controls, however, were less than those reported by the authors for West European Caucasians (2.9% vs 10%) (HoÈhlet et al, 1997), whereas no difference was seen between this study and the previous one (2.9% vs 1.7%) (Higuchi et al, 1998). Furthermore, we found no signi®cant increase of subjects carrying C, A, and T at positions -1031, -863, and -857, respectively (Table I). In this region the frequency of alleles -1031C (C at -1031), -863A (A at -863), and -857T (T at -857) is similar to that previously reported by Higuchi et al (1998) (12.6% vs 16.0% for -1031C; 15.5% vs 14.0%, -863A; 15.5% vs 17.7%, -857T). These results are quite different from those reported by HoÈhler et al (1997). In their report, 32% (20 in 62) of PsA patients have genotype G/A at -238, whereas 7% of controls (seven of 99) have the genotype (HoÈhler et al, 1997). We calculated on gene frequencies for the TNF-238A allele in PsA patients 16.1% from the data demonstrated. The discrepancy does not seem to depend on the racial difference, because gene frequencies for the TNF-238A allele in their controls were not different from the data by our or other studies (3.5% vs 2.3% or 2.0%) (HoÈhlet et al, 1997; Higuchi et al, 1998). Although a small number of PsA cases was investigated, this study clearly shows that promoter polymorphism at -238 of the TNF-a gene is not associated with PsA in the Japanese population as well as at other positions, including -1031, -863, -857, and -308.