Yuko Okudaira

Exome sequencing identifies novel rheumatoid arthritis-susceptible variants in the BTNL2

The butyrophilin-like protein 2 gene (BTNL2) within the class III region of the major histocompatibility complex genomic region was identified as a rheumatoid arthritis (RA) susceptibility gene by exome sequencing (19 RA cases) with stepwise filtering analysis, and then validated by Sanger sequencing and association analysis using 432 cases and 432 controls. Logistic regression of the Sanger-sequenced single-nucleotide variants in an association study of 432 cases and 432 controls showed that 12 non-synonymous single-nucleotide polymorphisms (SNPs) in BTNL2 were significantly associated with RA. The lowest P-values were obtained from three SNPs, rs41521946, rs28362677 and rs28362678, which were in absolute linkage disequilibrium: P=4.55E−09, odds ratio=1.88, 95% confidence interval=1.52–2.33. The BTNL2 locates on chromosome 6 between HLA-DRB1 and NOTCH4, and is 170 kb apart from these two genes. Although DRB1 and NOTCH4 were reported to be RA-susceptible, the three BTNL2 SNPs retained significant association with RA when evaluated by the logistic regression with the adjustment for RA-susceptible HLA-DRB1 alleles in Japanese or rs2071282-T in NOTCH4: P=0.0156 and P=0.00368, respectively. These results suggest that the three non-synonymous SNPs in BTNL2 confer RA risk independently from HLA-DRB1 and NOTCH4.

Associations between six classical HLA loci and rheumatoid arthritis: a comprehensive analysis.

Although the HLA region contributes to one-third of the genetic factors affecting rheumatoid arthritis (RA), there are few reports on the association of the disease with any of the HLA loci other than the DRB1. In this study we examined the association between RA and the alleles of the six classical HLA loci including DRB1. Six HLA loci (HLA-A, -B, -C, -DRB1, -DQB1 and -DPB1) of 1659 Japanese subjects (622 cases; 488 anti-cyclic citrullinated peptides (CCP) antibody (Ab) positive (82.6%); 103 anti-CCP Ab negative (17.4%); 31 not known and 1037 controls) were genotyped. Disease types and positivity/negativity for CCP autoantibodies were used to stratify the cases. Statistical and genetic assessments were performed by Fishers exact tests, odds ratio, trend tests and haplotype estimation. None of the HLA loci were significantly associated with CCP sero-negative cases after Bonferroni correction and we therefore limited further analyses to using only the anti CCP-positive RA cases and both anti-CCP positive and anti-CCP negative controls. Some alleles of the non-DRB1 HLA loci showed significant association with RA, which could be explained by linkage disequilibrium with DRB1 alleles. However, DPB1*02:01, DPB1*04:01 and DPB1*09:01 conferred RA risk/protection independently from DRB1. DPB1*02:01 was significantly associated with the highly erosive disease type. The odds ratio of the four HLA-loci haplotypes with DRB1*04:05 and DQB1*04:01, which were the high-risk HLA alleles in Japanese, varied from 1.01 to 5.58. C*07:04, and B*15:18 showed similar P-values and odds ratios to DRB1*04:01, which was located on the same haplotype. This haplotype analysis showed that the DRB1 gene as well as five other HLA loci is required for a more comprehensive understanding of the genetic association between HLA and RA than analyzing DRB1 alone.

Correction of the HLA‐DQB1*04:01:01 sequence at position 79 in exon 1

The HLA‐DQB1*04:01:01 sequence is corrected at position 79 in exon 1 (G > A, Ala > Thr).

Improved loop-mediated isothermal amplification for HLA-DRB1 genotyping using RecA and a restriction enzyme for enhanced amplification specificity

Our aim was to test and develop the use of loop-mediated isothermal amplification (LAMP) for HLA-DRB1 genotyping. Initially, we found that the conventional LAMP protocols produced non-specific and variable amplification results depending on the sample DNA conditions. Experiments with different concentrations of DNase in the reaction mixture with and without T4 DNA ligase-treated samples suggested that the strand displacement activity of DNA polymerase in LAMP, at least in part, started from randomly existing nicks because T4 DNA ligase treatment of sample DNA resulted in no amplification. Such non-specific amplification due to the randomly existing nicks was improved specifically by the addition of RecA of Escherichia coli and a restriction enzyme, for example, PvuII, to the reaction mixture. We applied the modified LAMP (mLAMP) (1) to detect specific HLA-DRB1 alleles by using only specific primers for amplification or (2) for genotyping in multiple samples with a multi-probe typing system. In the latter case, HLA-DRB1 genotyping was developed by combining the mLAMP with amplicon capture using polymorphic region-specific probes fixed onto the bottom of the wells of a 96-well plate and the captured amplicons visualized as a black spot at the bottom of the well. The multi-probe human leukocyte antigen (HLA) typing method and the specific HLA allele detection method could be applied for point-of-care testing due to no requirement for specific and expensive instruments.

Particular human leukocyte antigen alleles are associated with biochemical traits in the Japanese population

We analyzed genetic associations among 7 biochemical traits (fasting plasma glucose, HbA1c, total cholesterol, low-density lipoprotein [LDL] cholesterol, high-density lipoprotein cholesterol, triglyceride, and uric acid) and 6 HLA loci using 1,616 individuals who visited the Health Evaluation and Promotion Center at Tokai University Hospital. Significant differences between the individuals carrying particular HLA alleles and those not carrying the alleles in certain biochemical traits were observed by Mann-Whitney U test. In female subjects, DPB1*03:01 was significantly associated with HbA1c (p = 0.0000665), and DRB1*14:03 was associated with total cholesterol concentration (p = 0.0015). In male subjects, C*14:02 demonstrated significant associations with fasting plasma glucose with p values of 0.0041. By contrast, Fishers exact test indicated that female DRB1*14:03 was associated with a high concentration of total cholesterol (p = 000323, odds ratio [OR] = 4.32, 95% confidence interval [95% CI] = 1.83-10.36), whereas female DPB1*02:01 had a protective effect against a high concentration of LDL cholesterol (p =0.0043, OR = 0.41, 95% CI = 0.19-0.79). These associations have a statistical power of more than 0.8 and still retain significance after Bonferroni correction.

Aggregation of rare/low-frequency variants of the mitochondria respiratory chain-related proteins in rheumatoid arthritis patients

Exome sequencings were conducted using 59 patients having rheumatoid arthritis (RA) and 93 controls. After stepwise filtering, 107 genes showed less than 0.05 of P-values by gene-burden tests. Among 107 genes, NDUFA7 which is a subunit of the complex I in the mitochondrial respiratory chain was selected for further analysis based on previous reports. A case–control study was performed on the three single-nucleotide variants (SNVs) of NDUFA7 with 432 cases and 432 controls. An association was observed between NDUFA7 and RA with severe erosive arthritis. These results together with previous reports suggested the involvement of reactive oxygen species (ROS) in the pathogenesis of RA. In the next step, four SNVs from three genes related to the mitochondrial respiratory chain were selected, which is a major source of ROS, and conducted a case–control study. An association was observed based on a pathway-burden test comprising NDUFA7, SDHAF2, SCO1 and ATP5O: P=1.56E-04, odds ratio=2.16, 95% confidence interval=1.43–3.28. Previous reports suggested the involvement of ROS in the pathogenesis of RA. The aggregation of SNVs in the mitochondria respiratory chain suggests the pivotal role of those SNVs in the pathogenesis of RA with severe erosive arthritis.