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Although the exact pathogenesis of subacute sclerosing panencephalitis (SSPE) remains to be determined, our previous data suggested a genetic contribution to the host susceptibility to SSPE. During chronic viral infection, virus-specific cytotoxic T lymphocytes display poor effector functions. Since co-inhibitory molecules are involved in the suppression of T lymphocytes, we investigated whether single nucleotide polymorphisms (SNPs) of genes encoding co-inhibitory molecules contributed to a susceptibility to SSPE. Association studies on a total of 20 SNPs in 8 genes (CTLA4, CD80, CD86, PD1, PDL1, PDL2, BTLA and HVEM) and subsequent haplotype analysis of 4 SNPs in the PD1 genes were performed in Japanese and Filipino SSPE patients and controls. Then, we investigated a functional difference in promoter activity of two haplotypes and compared the expression levels of PD1 between SSPE and controls. The frequency of GCG(C) haplotype of PD1 containing -606G allele was significantly higher in SSPE patients than in controls both in Japanese and in Filipinos. The promoter activity was significantly higher in the construct with -606G allele than in that with -606A allele. The expression levels of PD1 were significantly higher in SSPE patients than in the controls. Our results suggested that the PD1 gene contributed to a genetic susceptibility to SSPE.

Interaction between Programmed cell death-1 (PD-1), a member of costimulatory molecules, and its receptors Programmed cell Death-1 Ligand 1 (PD-L1) and Programmed cell Death-1 Ligand 2 (PD-L2), play an important role in the negative regulation of immune reactions. It was shown that a polymorphism in a regulatory site of the PD-1 gene was associated with susceptibility to several autoimmune diseases in various ethnic groups, whereas the contribution of the PD-1 gene or its ligand genes to the onset of type 1 diabetes (T1D) mellitus in the Japanese population remains unknown. We first screened PD-1, PD-L1, and PD-L2 genes for polymorphisms in the Japanese population, and then investigated the frequencies of polymorphisms in patients with T1D mellitus in comparison with healthy controls. In total, we identified 26 polymorphic sites within these genes, and then 23 polymorphisms with minor allele frequencies greater than 5% were intensively analyzed for genotyping in the patients and the controls. As a result, allele and genotype frequencies of the polymorphism numbers 2, 3, 4, 5, 6, and 8 in the PD-1 gene were different to some extent between the patients and the controls with P < 0.05, which did not reach statistical significance after the correction of multiple comparisons. Allele or genotype frequencies of any SNPs in the PD-L1 or PD-L2 gene did not show differences between the patients and the controls. The frequencies of the estimated haplotypes, those of which consisted of polymorphism numbers 2, 3, 4, 5, 6, and 8 in the PD-1, were significantly different between the patients and the controls (P = 0.00095). The in vitro assessment for a transcription activity of each haplotype of the PD-1 gene by luciferase assay did not demonstrate a functional difference between the haplotypes. In conclusion, the genetic evaluation by association study demonstrated that the PD-1 gene was a predisposing gene to the development of T1D mellitus in the Japanese population.

The gene encoding interferon (IFN)-gamma, IFNG, is known as one of the candidate susceptibility genes for type 1 diabetes. In addition, cytokines, including IFN-gamma, play important roles in the pathogenesis of type 1 diabetes. Therefore, we focused on the Th1-specific T-box transcription factor gene (T-bet), which contributes to the induction of the hallmark Th1 cytokine, IFN-gamma. We first screened for polymorphisms in the T-bet gene and detected two microsatellite repeat polymorphisms located in intron 1 and the 3'- flanking region, and two single nucleotide polymorphisms, including a His33Gln substitution within the coding region. By association studies, the Gln-positive phenotype and (CA)14 allele in 3'-flanking region of T-bet were found to be associated with type 1 diabetes in the Japanese population. Furthermore, Gln33 T-bet showed a significantly higher transcriptional activity of the IFNG gene via a dual luciferase reporter assay. Our study suggests the first evidence of an association between type 1 diabetes and polymorphisms in the T-bet gene, and that variation in T-bet transcriptional activity may play a role in the development of type 1 diabetes, possibly through the effect on IFN-gamma production in Th1 cells., (Copyright 2004 Springer-Verlag)

A nonsense mutation at codon 95 (R95X) in the C9 gene is responsible for most Japanese C9 deficiency (C9D) cases, with a carrier frequency of 6.7%. Upon analysis of microsatellite markers and newly identified dinucleotide repeat number polymorphisms in the 3' flanking region of the C9 gene, a founder effect was demonstrated for the R95X mutation of the C9 gene in Japanese. Screening for the R95X mutation in Korean and Chinese individuals showed that the R95X carrier frequencies in Koreans and Chinese were 2.0% and 1.0%, respectively. Although homozygotes for the R95X mutation were not found in Korea or China, the shared haplotype of the dinucleotide repeat number polymorphisms appeared to be associated with the R95X mutation in the heterozygotes in Korea and China. The founder effect found in East Asians (Japanese, Koreans and Chinese) but not in Caucasians, as well as the haplotype sharing in only a small chromosomal interval, suggested that the R95X mutation of C9 gene was ancient and had occurred after the divergence of East Asians and Caucasians, and before migration of the Yayoi people to Japan. Since the mortality of meningococcal infections in complement-deficient patients is lower than that in normal individuals, a founder effect and a selective advantage in isolation might be the main reasons for the high frequency of the R95X mutation in Japan.

Deficiency of the ninth component of human complement (C9) is the most common complement deficiency in Japan but is rare in other countries. We studied the molecular basis of C9 deficiency in four Japanese C9-deficient patients who had suffered from meningococcal meningitis. Direct sequencing of amplified C9 cDNA and DNA revealed a nonsense substitution (CGA-->TGA) at codon 95 in exon 4 in the four C9-deficient individuals. An allele-specific polymerase chain reaction system designed to detect exclusively only one of the normal and mutant alleles indicated that all the four patients were homozygous for the mutation in exon 4 and that the parents of patient 2 were heterozygous. The common mutation at codon 95 in exon 4 might be responsible for most Japanese C9 deficiency.