Psoriasis is an immune-mediated genetic skin disease. The underlying pathomechanisms involve complex interaction between the innate and adaptive immune system. T cells interact with dendritic cells, macrophages, and keratinocytes, which can be mediated by their secreted cytokines. In the past decade, biologics targeting tumor necrosis factor-α, interleukin (IL)-23, and IL-17 have been developed and approved for the treatment of psoriasis. These biologics have dramatically changed the treatment and management of psoriasis. In contrast, various triggering factors can elicit the disease in genetically predisposed individuals. Recent studies suggest that the exacerbation of psoriasis can lead to systemic inflammation and cardiovascular comorbidity. In addition, psoriasis may be associated with other auto-inflammatory and auto-immune diseases. In this review, we summarize the risk factors, which can be divided into two groups (namely, extrinsic and intrinsic risk factors), responsible for the onset and exacerbation of psoriasis in order to facilitate its prevention.

The HLA-Cw6 antigen has been associated with psoriasis vulgaris despite racial and ethnic differences. However, it remains unclear whether it is the HLA-Cw6 antigen itself or a closely linked, hitherto unidentified, locus that predisposes to the disease. Here, in order to map the susceptibility locus for psoriasis vulgaris precisely within the HLA class I region, 11 polymorphic microsatellite markers distributed throughout a 1060 kb segment surrounding the HLA-C locus were subjected to association analysis in Japanese psoriasis vulgaris patients. Statistical analyses of the distribution and deviation from Hardy-Weinberg equilibrium of the allelic frequency at each micro-satellite locus revealed that the pathogenic gene for psoriasis vulgaris is located within a reduced interval of 111 kb spanning 89-200 kb telomeric of the HLA-C gene. In addition to three known genes, POU5F1, TCF19 and S, this 111 kb fragment contains four new, expressed genes identified in the course of our genomic sequencing of the entire HLA class I region. Therefore, these seven genes are the potential candidates for susceptibility to psoriasis vulgaris.

This is a Japanese retrospective single‐center study carried out between 1 January 2010 and 21 November 2018 at the Department of Dermatology in Jichi Medical University Hospital. The drug survival rate for six biologic agents used for the treatment of psoriasis was investigated. We reviewed the clinical records of 315 treatment series of 205 patients with moderate to severe psoriasis treated with adalimumab (103 cases), infliximab (70 cases), ustekinumab (66 cases), secukinumab (38 cases), brodalumab (12 cases) and ixekizumab (26 cases). In our study, ustekinumab revealed a trend towards higher drug survival among the six biologic agents. Ustekinumab had a higher drug survival rate than infliximab and secukinumab with significant differences by log–rank test among all patients and among biologic‐naive (bio‐naive) patients. There was no significant difference in drug survival between bio‐naive and biologic‐experienced (non‐naive) patients in the treatment courses with adalimumab, infliximab, ustekinumab, secukinumab and ixekizumab. The dose augmentation therapy in infliximab‐treated patients was associated with longer drug survival. Of all patients, 25 cases with generalized pustular psoriasis (GPP) were included, who functioned as the negative predictor for drug persistence with a hazard ratio of 1.87 (95% confidence interval, 1.12–3.11; P = 0.016). Our results reveal that ustekinumab had a superior drug survival, which is supported by the previous studies. Further studies are needed to clarify the efficacy of biologic agents on patients with GPP.

Apremilast is a novel oral phosphodiesterase‐4 inhibitor approved for treatment of plaque psoriasis and psoriatic arthritis in Japan in December 2016. We have treated a substantial number of patients with psoriasis with apremilast and investigated the length of the treatment period with apremilast (drug survival of apremilast) in 138 patients with psoriasis who were treated at the Department of Dermatology in Jichi Medical University Hospital from 1 March 2017 to 31 August 2018 using the Kaplan–Meier survival curve. The drug survival rate of apremilast at 1 year was 53.4%. The median length of the drug survival period was 453 days. There were no statistical differences in the drug survival rate in terms of the type of psoriasis, previous systemic treatment or presence of one or more adverse events. Drug efficacy was investigated in 115 patients who were followed for more than 16 weeks. There was no correlation between drug efficacy and sex, previous systemic treatment or presence of one or more adverse events; however, there was a correlation between drug efficacy and plaque size (P < 0.01, rs = −0.29). The result of our study indicates that apremilast is effective regardless of the history of prior systemic treatment, and it supports our previous finding that small plaque‐type psoriasis is more sensitive to treatment with apremilast.

Apremilast is a novel oral phosphodiesterase 4 inhibitor effective for psoriasis. It regulates the production of pro-inflammatory mediators. Apremilast was approved in December 2016 in Japan; however, its efficacy and safety in a real-world setting among Japanese patients have not been reported. We report on 44 patients treated with apremilast between March and October 2017. The median treatment duration was 25 weeks (range, 2-33). Thirty-five patients (79.5%) continued the drug for at least 23 weeks, and five (11.4%) achieved a Psoriasis Area and Severity Index 100 response within 12 weeks. Nine patients discontinued the drug within 24 weeks mainly due to insufficient efficacy (n = 3) and adverse events (n = 4). Seven patients continued their previous systemic therapies such as cyclosporin (n = 1), methotrexate (n = 1), etretinate + methotrexate (n = 1) and biologics (n = 4) combined with apremilast. Of these patients, 55.9% had at least one adverse event although no severe adverse events. The most common adverse event was diarrhea (31.8%), followed by nausea (25.0%), headache (13.6%), abdominal discomfort (6.8%) and vomiting (6.8%). The proportion of diarrhea in our patients was higher than those of previous clinical trials. Among 10 patients with psoriatic arthritis, apremilast did not improve joint pain in nine (90%). To investigate the relationship between treatment efficacy and plaque size, we defined a small plaque as an individual rash diameter of 1 inch or less. The efficacy of apremilast was greater in patients with small plaques than in patients with large plaques.

A multicenter randomized controlled study was conducted to assess the long-term efficacy and safety of cyclosporin A therapy for psoriasis using either a continuous or an intermittent regimen. Initially, both regimens consisted of 3-5 mg/kg/day administration of CyA. Once remission was obtained, CyA dose was maintained between 0.5 and 3 mg/kg/day under the continuous regimen, while under the intermittent regimen, CyA dose was tapered off and, when necessary, topical corticosteroids were used until relapse occurred. Thirty-one patients were followed for at least 48 months (mean follow-up period: 55.9+/-4.6 months): 15 received continuous therapy, and 16 received intermittent therapy. With both regimens, the PASI (Psoriasis Area and Severity Index) score was maintained at 5-12 points throughout the follow-up period. The score was decreased by more than 70% from baseline with both regimens: the responses between them were not significantly different. However, overall control of psoriasis, as assessed from the averaged PASI score, was better in the patients receiving continuous therapy. Although the overall frequency of adverse reactions was similar for the two regimens, cancer occurred in two patients on continuous therapy (gastric cancer and hepatocellular carcinoma in one patient each). We could not, however, definitely attribute the cancers in the two patients to continuous therapy itself. There was a significantly higher incidence of renal impairment in elderly patients receiving either regimen when compared with younger patients. In conclusion, CyA administered to psoriasis patients under both regimens exhibited long-term efficacy and tolerability. Despite a lower overall efficacy, it seems proper to conclude that intermittent therapy is more useful than continuous therapy due to the occurrence of malignancies with continuous therapy. Further investigation is required to determine whether intermittent therapy is really safer than continuous therapy, and, if so, how it should be designed to minimize long-term adverse reactions and achieve overall control comparable to that of continuous CyA therapy.

HLA alleles in generalized pustular psoriasis (GPP) were investigated to clarify the etiology and/or pathogenesis of this disease. Not only serological typing of HLA class I and II antigens but also genotyping of HLA class II alleles were carried out in twenty-six unrelated Japanese patients with GPP. These patients were classified according to their history of psoriasis vulgaris (PV). Serological typing revealed a significantly high incidence of HLA-Cw1 (Pc = 0.04) in the patients as compared with Japanese healthy controls. The frequency of HLA-B46 was particularly high in the patients with GPP and a previous history of PV. Genotyping of HLA class II alleles showed a highly significant increase in HLA-DQB1*0303 (Pc = 0.01) in the patients vs. the healthy controls. In particular, HLA-DQB1*0303 was significantly more frequent in the patients with no prior history of PV than in those with a history of PV. Analysis on linkage disequilibrium showed remarkably different patterns for HLA class II haplotypes between the patients and the healthy controls. Based on the comparative analysis among the amino acid sequences of the beta 1-domain of the HLA-DQB1*03 alleles, proline at residue 55 was suggested to be important as a common amino acid for determination of the susceptibility to GPP. These results revealed not only an association between the etiology and/or pathogenesis of GPP and HLA, but also different mechanisms of the immune response between the patients with GPP and PV.

HLA class I and class II alleles of 32 Japanese patients with postherpetic neuralgia (PHN) and 136 healthy controls were analyzed by serological (class I) and DNA (class II) typing for any significance in the susceptibility to varicella-zoster virus (VZV). We recognized positive associations of the development of PHN with the HLA class I antigens HLA-A33 and -B44, and the HLA-A33-B44 haplotype. This haplotype is tightly linked to DRB1*1302 in a Japanese healthy population. However, no significant association between PHN and HLA class II alleles was observed with no linkage of the HLA haplotype HLA-A33-B44 to HLA-DRB1*1302 in the patients with PHN. These findings suggest that HLA class I gene may genetically control the immune response against VZV in the pathogenesis of PHN.