Objectives A previous publication in Chinese leprosy patients showed that the HLA-B*13:01 allele is a strong genetic marker for dapsone-induced drug hypersensitivity reactions, however there are no data describing whether HLA-B*13:01 is a valid marker for prediction of dapsone-induced drug hypersensitivity reactions in other ethnicities or nonleprosy patients. The aim of this study is to investigate whether there is an association between HLA genotypes and dapsone-induced severe cutaneous adverse reactions (SCARs) in Thai nonleprosy patients. Patients and methods HLA-B genotypes of 15 patients with dapsone-induced SCARs (11 drug reaction with eosinophilia and systemic symptoms, 4 Stevens–Johnson syndrome/toxic epidermal necrolysis), 29 control patients, and 986 subjects from the general Thai population were determined by the reverse PCR sequence-specific oligonucleotides probe. Results The HLA-B*13:01 allele was significantly associated with dapsone-induced SCARs compared with dapsone-tolerant controls (odds ratio: 54.00, 95% confidence interval: 7.96–366.16, P=0.0001) and the general population (odds ratio: 26.11, 95% confidence interval: 7.27–93.75, P=0.0001). In addition, HLA-B*13:01 associated with dapsone-induced SJS-TEN (OR: 40.50, 95% confidence interval: 2.78-591.01, P=0.0070) and DRESS (OR: 60.75, 95% confidence interval: 7.44-496.18, P=0.0001). Conclusion This study demonstrated an association between HLA-B*13:01 and dapsone-induced SCARs including Stevens–Johnson syndrome/toxic epidermal necrolysis and drug reaction with eosinophilia and systemic symptoms in nonleprosy patients. Moreover, these results suggest that the HLA-B*13:01 allele may be a useful genetic marker for prediction of dapsone-induced SCARs in Thai and Han-Chinese populations.

Background: The aim of this study was to investigate the predisposition to different types of allopurinol-induced cutaneous adverse drug reactions (CADR), including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN) (SJS-TEN, n=13), drug reaction with eosinophilia and systemic symptoms (DRESS, n=10) and severe Maculopapular eruption (MPE) (n=7), conferred by HLA-B*58:01 in a Thai population. METHODS: This case-controlled association study compares 30 patients with allopurinol-induced CADR, allopurinol-tolerant control patients (n=100) and a Thai general population (n=1,095). Patients’ human leukocyte antigen type B (HLA-B) alleles were genotyped by using a two-stage sequence-specific oligonucleotide probe system. RESULTS: Of a total 30 patients with CADR due to allopurinol, 29 (96.7%) patients were found to be at least heterozygous for HLA-B*58:01, while was found only 4.0% in allopurinol-tolerant patients (p<0.001). Odds ratio (OR) for the association of HLA-B*58:01 with allopurinol-induced CADR in this population was 696.0 (95% CI: 74.8-6475.0). The HLA-B*58:01 allele was present in all patients with allopurinol-induced SJS-TEN (OR=579.0, 95%CI: 29.5-11362.7, p<0.001) and DRESS (OR 430.3, 95%CI: 22.6-8958.9, p<0.001). Additionally, OR of HLA-B*58:01 was highly significant in the allopurinol-induced MPE patients (OR 144.0, 95%CI: 13.9-1497.0, p<0.001), CONCLUSION: In this study we confirmed the association between HLAB*58:01 and allopurinol-induced SJS-TEN in a Thai population. In addition, we identified an association between HLA-B*58:01 and allopurinol-induced DRESS and MPE in this population. Therefore, HLA-B*58:01 can be used as a pharmacogenetic marker for allopurinol-induced CADR including SJS-TEN, DRESS and MPE. These results suggest that screening for HLA-B*58:01 alleles in patients who will be treated with allopurinol would be clinically helpful in preventing the risk of developing CADR in a Thai patients.

Human leukocyte antigen (HLA) class I and II are known to have association with severe cutaneous adverse reactions (SCARs) when exposing to certain drug treatment. Due to genetic differences at population level, drug hypersensitivity reactions are varied, and thus common pharmacogenetics markers for one country might be different from another country, for instance, HLA-A*31:01 is associated with carbamazepine (CBZ)-induced SCARs in European and Japanese while HLA-B*15:02 is associated with CBZ-induced Stevens–Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) among Taiwanese and Southeast Asian. Such differences pose a major challenge to prevent drug hypersensitivity when pharmacogenetics cannot be ubiquitously and efficiently translated into clinic. Therefore, a population-wide study of the distribution of HLA-pharmacogenetics markers is needed. This work presents a study of Thai HLA alleles on both HLA class I and II genes from 470 unrelated Thai individuals by means of polymerase chain reaction sequence-specific oligonucleotide (PCR-SSO) in which oligonucleotide probes along the stretches of HLA-A, -B, -C, -DRB1, -DQA1, and -DQB1 genes were genotyped. These 470 individuals were selected according to their regional locations, which were from North, Northeast, South, Central, and a capital city, Bangkok. Top ranked HLA alleles in Thai population include HLA-A*11:01 (26.06%), -B*46:01 (14.04%), -C* 01:02 (17.13%), -DRB1*12:02 (15.32%), -DQA1*01:01 (24.89%), and -DQB1*05:02 (21.28%). The results revealed that the distribution of HLA-pharmacogenetics alleles from the South had more HLA-B75 family that a typical HLA-B*15:02 pharmacogenetics test for SJS/TEN screening would not cover. Besides the view across the nation, when compared HLA alleles from Thai population with HLA alleles from both European and Asian countries, the distribution landscape of HLA-associated drug hypersensitivity across many countries could be observed. Consequently, this pharmacogenetics database offers a comprehensive view of pharmacogenetics marker distribution in Thailand that could be used as a reference for other Southeast Asian countries to validate the feasibility of their future pharmacogenetics deployment.

Human leukocyte antigen (HLA) encoded by the HLA gene is an important modulator for immune responses and drug hypersensitivity reactions as well. Genetic polymorphisms of HLA vary widely at population level and are responsible for developing severe cutaneous adverse drug reactions (SCARs) such as Stevens–Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), maculopapular exanthema (MPE). The associations of different HLA alleles with the risk of drug induced SJS/TEN, DRESS and MPE are strongly supportive for clinical considerations. Prescribing guidelines generated by different national and international working groups for translation of HLA pharmacogenetics into clinical practice are underway and functional in many countries, including Thailand. Cutting edge genomic technologies may accelerate wider adoption of HLA screening in routine clinical settings. There are great opportunities and several challenges as well for effective implementation of HLA genotyping globally in routine clinical practice for the prevention of drug induced SCARs substantially, enforcing precision medicine initiatives.

SCARs are rare and life-threatening hypersensitivity reactions. In general, the increased duration of hospital stays and the associated cost burden are common issues, and in the worst-case scenario, they can result in mortality. SCARs are delayed T cell-mediated hypersensitivity reactions. Recovery can take from 2 weeks to many months after dechallenging the culprit drugs. Genetic polymorphism of the HLA genes may change the selection and presentation of antigens, allowing toxic drug metabolites to initiate immunological reactions. However, each SCARs has a different onset latency period, clinical features, or morphological pattern. This explains that, other than HLA mutations, other immuno-pathogenesis may be involved in drug-induced severe cutaneous reactions. This review will discuss the clinical morphology of various SCARs, various immune pathogenesis models, diagnostic criteria, treatments, the association of various drug-induced reactions and susceptible alleles in different populations, and the successful implementation of pharmacogenomics in Thailand for the prevention of SCARs.

The HLA-B∗15:02 allele has been reported to have a strong association with carbamazepine-induced Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) in Thai patients. The HLA-B alleles associated with carbamazepine-induced maculopapular exanthema (MPE) and the drug reaction with eosinophilia and systemic symptoms (DRESS) among the Thai population have never been reported. The aim of the present study was to carry out an analysis of the involvement of HLA-B alleles in carbamazepine-induced cutaneous adverse drug reactions (cADRs) in the Thai population. A case-control study was performed by genotyping the HLA-B alleles of Thai carbamazepine-induced hypersensitivity reaction patients (17 MPE, 16 SJS/TEN, and 5 DRESS) and 271 carbamazepine-tolerant controls. We also recruited 470 healthy Thai candidate subjects who had not taken carbamazepine. HLA-B∗15:02 showed a significant association with carbamazepine-induced MPE (P=0.0022, odds ratio (OR) (95% confidence interval [CI]) = 7.27 (2.04–25.97)) and carbamazepine-induced SJS/TEN (P=4.46×10−13; OR (95% CI) = 70.91(19.67–255.65)) when compared with carbamazepine-tolerant controls. Carbamazepine-induced SJS/TEN also showed an association with HLA-B∗15:21 allele (P=0.013; OR (95% CI) = 9.54 (1.61–56.57)) when compared with carbamazepine-tolerant controls. HLA-B∗58:01 allele was significantly related to carbamazepine-induced MPE (P=0.007; OR (95% CI) = 4.73 (1.53–14.66)) and DRESS (P=0.0315; OR (95% CI) = 7.55 (1.20–47.58)) when compared with carbamazepine-tolerant controls. These alleles may serve as markers to predict carbamazepine-induced cADRs in the Thai population.