HLA-B*40:02 and DRB1*04:03 are risk factors for oxcarbazepine-induced maculopapular eruption

HLA-B allele frequencies and implications for pharmacogenetics in the Kuwaiti population

Objective: This study explores the frequency of human leukocyte antigen (HLA) genes, particularly HLA-B alleles, within the Kuwaiti population. We aim to identify alleles with known associations to adverse drug reactions (ADRs) based on existing literature. We focus on the HLA-B gene due to its well-documented associations with severe cutaneous adverse reactions and the extensive pharmacogenetic research supporting its clinical relevance.

Methods

We utilized the HLA-HD tool to extract, annotate, and analyse HLA-B alleles from the exome data of 561 Kuwaiti individuals, sequenced on the Illumina HiSeq platform. HLA typing was conducted using the HLA-HD tool with a reference panel from the IPD-IMGT/HLA database. The major HLA-B pharmacogenetic markers were obtained from the HLA Adverse Drug Reaction Database, focusing on alleles with significant ADR associations in published literature.

Results

The distribution of HLA-B alleles in the Kuwaiti population revealed that the most frequent alleles were HLA-B*50:01 (10.52%), HLA-B*51:01 (9.89%), HLA-B*08:01 (6.06%), HLA-B*52:01 (4.55%), HLA-B*18:01 (3.92%), and HLA-B*41:01 (3.65%). Notably, alleles HLA-B*13:01, HLA-B*13:02, HLA-B*15:02, HLA-B*15:13, HLA-B*35:02, HLA-B*35:05, HLA-B*38:01, HLA-B*40:02, HLA-B*44:03, HLA-B*51:01, HLA-B*57:01 and HLA-B*58:01 were identified with known associations to various ADRs. For example, HLA-B*51:01 was associated with clindamycin, phenobarbital, and phenytoin, and was found in 18% of individuals.

Conclusion

Our study enriches the regional genetic landscape by delineating HLA-B allele variations within Kuwait and across the Arabian Peninsula. This genetic insight, along with the identification of markers previously linked to drug hypersensitivity, provides a foundation for future pharmacogenetic research and potential personalized medicine strategies in the region.

Update on HLA-B*15:02 allele associated with adverse drug reactions

HLA alleles, part of the major histocompatibility complex, are strongly associated with adverse drug reactions (ADRs). This review focuses on HLA-B*15:02 and explores its association with ADRs in various ethnic populations and with different drugs, aiming to provide insights into the safe clinical use of drugs and minimize the occurrence of ADRs. Furthermore, the review explores the potential mechanisms by which HLA-B*15:02 may be associated with ADRs, aiming to gain new insights into drug modification and identification of haptens. In addition, it analyzes the frequency of the HLA-B*15:02, genotyping methods, cost-effectiveness and treatment measures for adverse reactions, thereby providing a theoretical basis for formulating clinical treatment plans.

Genotyping for HLA risk alleles versus patch tests to diagnose anti-seizure medication induced cutaneous adverse drug reactions

Aim: To provide a comparison of genotyping for HLA risk alleles versus patch testing to determine which of these two tests is a better diagnostic tool for cutaneous hypersensitivity reactions caused by anti-seizure medication. Methods: A literature study was performed in PubMed to assess the sensitivity and specificity of HLA genotyping and patch tests for identifying anti-seizure medication induced cutaneous hypersensitivity reactions. Results: This study shows that HLA-B*15:02 genotyping shows high sensitivity for carbamazepine-induced SJS/TEN, especially in Han Chinese and Southeast Asian patients (66.7-100.0%) whereas the sensitivity of patch tests (0.0-62,5%), HLA-A*31:01 (0-50%) and HLA-B*15:11 (18.2-42.9%) are lower. On the contrary, for carbamazepine and phenytoin induced DRESS, patch tests (respectively 70.0-88.9% and 14.3-70.0%) show higher sensitivity than HLA tests (0-66.7% and 0-12.7%). Also for lamotrigine-induced DRESS patch tests perform better than HLA-B*15:02 (33.3-40.0 versus 0%). For anti-seizure medication induced MPE and for oxcarbazepine-induced SCARs more studies are needed. Conclusion: Use of HLA-B genotyping may aid clinicians in the diagnosis of carbamazepine, phenytoin, lamotrigine and oxcarbazepine induced SJS/TEN, particularly in Han Chinese and Southeast Asian patients. On the other hand, patch tests seem to perform better in the diagnosis of carbamazepine and phenytoin induced DRESS.

Telemedicine in epilepsy and encephalitis: previous research and indication guidelines in Korea

Telemedicine is an emerging field of medicine that has become more important during the coronavirus disease 2019 (COVID-19) pandemic era and is being studied actively in various medical fields. In neurology, the introduction of telemedicine is accelerating worldwide under the label of teleneurology. So far, few studies have been conducted on telemedicine for patients with epilepsy. In nonmetropolitan areas, video-based clinics have been demonstrated to be effective for seizure control, and smartphone-based diagnosis has also been confirmed to be accurate. Indeed, after the onset of the COVID-19 pandemic, telemedicine has been used to treat patients with epilepsy around the world. Few studies have examined the use of telemedicine for patients with autoimmune encephalitis. One showed that telephone-based evaluation is sufficient to assess the cognitive reserve of leucine-rich glioma inactivated-1-antibody encephalitis patients, thereby diagnosing their dementia. Telephone-based outpatient clinics are temporarily permitted under Korean medical law, and telemedicine can be attempted for clinically stable patients with epilepsy in Korea. In addition, patients with autoimmune encephalitis in stable or improving status may also be candidates for treatment with telemedicine. This review presents evidence for the safety and efficacy of telemedicine to treat epilepsy and encephalitis patients and discusses indication guidelines. Based on our literature review and current Korean medical law, we suggest tentative guidelines for telemedicine in the fields of epilepsy and autoimmune encephalitis.

HLA Allele-Restricted Immune-Mediated Adverse Drug Reactions: Framework for Genetic Prediction

Human leukocyte antigen (HLA) is a hallmark genetic marker for the prediction of certain immune-mediated adverse drug reactions (ADRs). Numerous basic and clinical research studies have provided the evidence base to push forward the clinical implementation of HLA testing for the prevention of such ADRs in susceptible patients. This review explores current translational progress in using HLA as a key susceptibility factor for immune ADRs and highlights gaps in our knowledge. Furthermore, relevant findings of HLA-mediated drug-specific T cell activation are covered, focusing on cellular approaches to link genetic associations to drug-HLA binding as a complementary approach to understand disease pathogenesis. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Association between the HLA-B*1502 gene and mild maculopapular exanthema induced by antiepileptic drugs in Northwest China

BACKGROUND

The relationship between the HLA-B*1502 gene and maculopapular exanthema (MPE) induced by antiepileptic drugs (AEDs) has not yet been elucidated. In this study, we investigated the association between AED-induced MPE (AED-MPE) and the HLA-B*1502 gene in patients in Northwest China.

METHODS

We enrolled 165 subjects including nine patients with AED-MPE and 156 AED-tolerant patients as controls. HLA-B*1502 gene polymorphism was detected using digital fluorescence molecular hybridization (DFMH). The results of HLA genotyping were expressed as positive or negative for the HLA-B*1502 allele. An analysis of AED-MPE risk factors was performed using binary logistic regression, and differences in genotype frequencies between groups were assessed with the continuity correction chi-square test.

RESULTS

We found that the HLA-B*1502 gene was a risk factor for AED-MPE (P = 0.028). The incidence of MPE induced by the two types of AEDs was different, and the incidence of aromatic AEDs use was higher that of non-aromatic AEDs use (P = 0.025). The comparison of the gene frequencies of the HLA-B*1502 allele between the two groups taking aromatic AEDs was also statistically significant (P = 0.045). However, there were no significant differences in terms of age, gender, ethnicity, or region in patients with MPE induced by AEDs. In addition, no association between the HLA-B1502 allele and CBZ- or OXC-induced MPE was found.

CONCLUSIONS

In northwestern China, the HLA-B*1502 allele was associated with aromatic AED-MPE. Since MPE can develop into Stevens-Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN), the HLA-B*1502 gene should be evaluated before administering AEDs.

Population pharmacokinetic model development and its relationship with adverse events of oxcarbazepine in adult patients with epilepsy

This study aimed to develop a pharmacokinetic (PK) model of oxcarbazepine (OXC) and analyse the relationship between monohydroxylated derivative (MHD), an active metabolite of OXC, and the adverse events of OXC. We obtained 711 OXC samples from 618 patients with epilepsy who were enrolled in the Epilepsy Registry Cohort of Seoul National University Hospital from February 2011 to January 2014. The plasma PK model was developed using a nonlinear mixed-effect modelling method with NONMEM (ver 7.3). A one-compartment model with a first-order absorption model and proportional residual error adequately described the MHD concentration–time profiles. The only covariate incorporated for CL/F and V/F was body weight. Of the 447 patients analysed, 28 (6.26%) had dose-related adverse events (DRAEs), which were dizziness, somnolence, headache, and diplopia. For DRAE occurrence, the cut-off values of the MHD trough and AUC were 12.27 mg/L (specificity 0.570, sensitivity 0.643) and 698.5 mg h/L (specificity, sensitivity 0.571), respectively. Multivariate analysis showed the sole dizziness symptom was significantly associated with both the MHD trough and the AUC (p = 0.013, p = 0.038, respectively). We newly developed a population PK model using sparse sampling data from patients with epilepsy, and the model better reflects the actual clinical situation.

HLA Risk Alleles in Aromatic Antiepileptic Drug-Induced Maculopapular Exanthema

To characterize human leukocyte antigen (HLA) loci as risk factors in aromatic antiepileptic drug-induced maculopapular exanthema (AED-MPE). A case-control study was performed to investigate HLA loci involved in AED-MPE in a southern Han Chinese population. Between January 2007 and June 2019, 267 patients with carbamazepine (CBZ), oxcarbazepine (OXC), or lamotrigine (LTG) associated MPE and 387 matched drug-tolerant controls from six centers were enrolled. HLA-A/B/C/DRB1 genotypes were determined using sequence-based typing. Potential risk alleles were validated by meta-analysis using data from different populations and in silico analysis of protein-drug interactions. HLA-DRB1*04:06 was significantly associated with OXC-MPE (p = 0.002, p _c = 0.04). HLA-B*38:02 was associated with CBZ-MPE (p = 0.03). When pooled, HLA-A*24:02, HLA-A*30:01, and HLA-B*35:01 additionally revealed significant association with AED-MPE. Logistic regression analysis showed a multiplicative interaction between HLA-A*24:02 and HLA-B*38:02 in CBZ-MPE. Meta-analysis of data from different populations revealed that HLA-24*:02 and HLA-A*30:01 were associated with AED-MPE (p = 0.02 and p = 0.04, respectively). In silico analysis of protein-drug interaction demonstrated that HLA-A*24:02 and HLA-A*30:01 had higher affinities with the three aromatic AEDs than the risk-free HLA-A allele. HLA-DRB1*04:06 showed relatively specific high affinity with S-monohydroxy derivative of OXC. HLA-DRB1*04:06 is a specific risk allele for OXC-induced MPE in the Southern Han Chinese. HLA-A*24:02, possibly HLA-A*30:01, are common risk factors for AED-MPE. The multiplicative risk potential between HLA-A*24:02 and HLA-B*38:02 suggests that patients with two risk alleles are at greater risk than those with one risk allele. Inclusion of these HLA alleles in pre-treatment screening would help estimating the risk of AED-MPE.

Diagnostic Test Criteria for HLA Genotyping to Prevent Drug Hypersensitivity Reactions: A Systematic Review of Actionable HLA Recommendations in CPIC and DPWG Guidelines

Introduction

Certain HLA variants are associated with an increased risk of hypersensitivity reactions to specific drugs. Both the Clinical Pharmacogenetics Implementation Consortium (CPIC) and the Dutch Pharmacogenetics Working Group (DPWG) have issued actionable HLA gene - drug interaction guidelines but diagnostic test criteria remain largely unknown. We present an overview of the diagnostic test criteria of the actionable HLA - drug pairs.

Methods

A systematic literature search was conducted in PubMed, Embase, Web of Science and Cochrane Library. Original case-control and cohort studies were selected and sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and number needed to genotype (NNG) were calculated for the actionable HLA-drug pairs.

Results

In general, the HLA tests show high specificity and NPV for predicting hypersensitivity reactions. The sensitivity of HLA tests shows a wide range, from 0-33% for HLA-B*1502 testing to predict lamotrigine induced SJS/TEN up to 100% for HLA-B*5701 to predict immunologically confirmed abacavir hypersensitivity syndrome (ABC-HSR). PPV is low for all tests except for HLA-B*5701 and ABC-HSR which is approximately 50%. HLA-B*5701 to predict ABC-HSR shows the lowest NNG followed by HLA-B*5801 for allopurinol induced severe cutaneous adverse drug reactions and HLA-B*1502 for carbamazepine induced SJS/TEN.

Discussion

This is the first overview of diagnostic test criteria for actionable HLA-drug pairs. Studies researching HLA genes and hypersensitivity are scarce for some of the HLA-drug pairs in some populations and patient numbers in studies are small. Therefore, more research is necessary to calculate the diagnostic test criteria more accurately.

HLAs associated with perampanel-induced psychiatric adverse effects in a Korean population

Perampanel (PER) is a new-generation antiepileptic drug that has an occasional but significant shortcoming, psychiatric adverse effects (PAEs). Recently, antiepileptic drug-related adverse reactions, such as skin rash and even PAEs, have been discovered to be correlated with certain human leukocyte antigen (HLA) types. Thus, we aimed to analyze specific HLA alleles as risk factors for PER-PAEs. We prospectively enrolled 17 patients with epilepsy who were prescribed PER between May 2016 and Jul 2018 at Seoul National University Hospital and developed PAEs while taking PER. Their HLA types were analyzed compared to those of 19 patients in the PAE-tolerant group and the general Korean population. In silico docking was performed with two different computational programs, AutoDock Vina and SwissDock, to theoretically evaluate the binding affinity of PER in the grooves of the specific HLA alleles. The HLA-DQB1*06:01, DRB1*08:03, and B*54:01 alleles were significantly associated with the patients who developed PER-PAEs compared with the general Korean population (odds ratio [OR] 3.94, p = 0.008, OR 9.24, p = 0.037, and OR 3.25, p = 0.041, respectively). As a haplotype, the combination of the three alleles was significantly more frequent in the PER-PAE group than in both the PER-tolerant group and the general Korean population. DQB1*06:01 and B*54:01 also demonstrated higher docking scores with PER than other alleles. This is the first study to analyze the association of PER-PAEs with specific HLA genotypes. Our results suggest that an HLA-associated genetic predisposition and a possible immunological mechanism are involved in the occurrence of PER-PAEs.

The Association Between HLA-A*03:01 and HLA-B*07:02 Alleles and Oxcarbazepine-induced Maculopapular Eruption in the Uighur Chinese Population

PURPOSE

To determine genetic associations between oxcarbazepine (OXC)-induced maculopapular eruption (MPE) and human leukocyte antigen (HLA) variants in the Uighur Chinese population.

METHODS

A total of 208 patients were enrolled in this study, including 20 subjects with OXC-induced MPE (case group) and 188 OXC-tolerant patients (control group). We detected the whole sequence of the HLA alleles in the 208 Uighur patients using next-generation sequencing (NGS).

RESULTS

The carried rate of HLA-A*03:01 was significantly different between the OXC-induced MPE group and the tolerant group (7/20, 35% versus 4/188, 2.13%; P = 0.000, odds ratio [OR] = 24.77, 95% confidence interval [CI] = 6.41-95.65). Additionally, the carried rate of HLA-B*07:02 was significantly different between the OXC-induced MPE group and the tolerant group (3/20, 15% versus 2/188, 0.011%; P = 0.000, odds ratio [OR] = 16.41, 95% confidence interval (CI) = 2.56-105.09).

CONCLUSIONS

HLA-A*03:01 and HLA-B*07:02 may be the risk alleles for MPE in the Uighur Chinese population.

Novel genetic and epigenetic factors of importance for inter-individual differences in drug disposition, response and toxicity

Individuals differ substantially in their response to pharmacological treatment. Personalized medicine aspires to embrace these inter-individual differences and customize therapy by taking a wealth of patient-specific data into account. Pharmacogenomic constitutes a cornerstone of personalized medicine that provides therapeutic guidance based on the genomic profile of a given patient. Pharmacogenomics already has applications in the clinics, particularly in oncology, whereas future development in this area is needed in order to establish pharmacogenomic biomarkers as useful clinical tools. In this review we present an updated overview of current and emerging pharmacogenomic biomarkers in different therapeutic areas and critically discuss their potential to transform clinical care. Furthermore, we discuss opportunities of technological, methodological and institutional advances to improve biomarker discovery. We also summarize recent progress in our understanding of epigenetic effects on drug disposition and response, including a discussion of the only few pharmacogenomic biomarkers implemented into routine care. We anticipate, in part due to exciting rapid developments in Next Generation Sequencing technologies, machine learning methods and national biobanks, that the field will make great advances in the upcoming years towards unlocking the full potential of genomic data.

Human leukocyte antigen associations in postural tachycardia syndrome

Associations between human leukocyte antigen (HLA) and postural orthostatic tachycardia syndrome (POTS) have not been investigated. We included patients diagnosed with POTS and showing orthostatic heart rate increases ≥ 50 during orthostatic vital sign measurement or experiencing syncope/near-syncope while standing (prominent POTS; n = 17). DQB1*06:09 was present in seven (41%) patients, a significantly higher percentage than in healthy Koreans (7%; odds ratio [OR] 8.7, 95% confidence interval [CI] 3.1-24.3, corrected P = 3.2 × 10^-4) and epilepsy controls (8%; OR 7.9, 95% CI 2.7-23.5, corrected P = 3.2 × 10^-4). Six (35.3%) carried the A*33:03-B*58:01-C*03:02-DRB1*13:02-DQB1*06:09 haplotype. The results signify an autoimmune etiology in prominent POTS.

Association between HLA-A*3201 allele and oxcarbazepine-induced cutaneous adverse reactions in Eastern Han Chinese population

PURPOSE

To determine genetic associations between oxcarbazepine (OXC)-induced cutaneous adverse drug reactions (cADRs) and human leukocyte antigen (HLA) variants in the Eastern Han Chinese population.

METHODS

A total of 120 patients were enrolled in this study, including 30 subjects with OXC-induced cADRs (case group) and 90 OXC-tolerant patients (control group). High-resolution HLA genotyping was conducted for HLA-A, HLA-B, HLA-C, and HLA-DRB1, and allele frequencies were compared.

RESULTS

No patient carried the HLA-B *1502 allele in the case group, the frequency of HLA-B *1502 allele in the control group was 6.1%. HLA-A*3201 allele was detected in 13.3% of 30 patients with OXC-induced cADRs (4/30) and 0% of 90 OXC-tolerant patients (0/90). The difference in HLA-A*3201 frequency between the two groups was statistically significant [P = 0.004, odds ratio (OR) = 15.877, 95% confidence interval (CI) = 1.817-138.720].

CONCLUSIONS

Eastern Han Chinese patients with the HLA-A*3201 allele may be more susceptible to OXC-induced cADRs, while the HLA-B*1502 allele is not correlated with it. The precise association between HLA alleles and OXC-induced cADRs warrants further study.

Safety and tolerability profile of new antiepileptic drug treatment in children with epilepsy

INTRODUCTION

Treatment of pediatric epilepsy requires a careful evaluation of the safety and tolerability profile of antiepileptic drugs (AEDs) to avoid or minimize as much as possible adverse events (AEs) on various organs, hematological parameters, and growth, pubertal, motor, cognitive and behavioral development.

AREAS COVERED

Treatment-emergent AEs (TEAEs) reported in the literature 2000-2018 regarding second- and third-generation AEDs used in the pediatric age, with exclusion of the neonatal period that exhibits specific peculiarities, have been described on the basis of their frequency, severity/tolerability, and particular association with a given AED.

EXPERT OPINION

Somnolence/sedation and behavioral changes, like irritability and nervousness, are among the most commonly observed TEAEs associated with almost all AEDs. Lamotrigine, Gabapentin, Oxcarbazepine, and Levetiracetam appear to be the best-tolerated AEDs with a ≤2% withdrawal rate, while Tiagabine and Everolimus are discontinued in up to >20% of the patients because of intolerable TEAEs. For some AEDs, literature data are scanty to draw a high-level evidence on their safety and tolerability profile. The reasons are: insufficient population size, short duration of treatments, or lack of controlled trials. A future goal is that of identifying clearer, easier, and more homogeneous methodological strategies to facilitate AED testing in pediatric populations.

Potential cause-effect relationship between insulin autoimmune syndrome and alpha lipoic acid: Two case reports

OBJECTIVES

Insulin autoimmune syndrome (IAS) or Hirata disease is a rare cause of autoimmune hypoglycemia with apparent high insulin levels and anti-insulin autoantibodies and was first described by Hirata in Japan in 1970. IAS cases are usually related to exposure to sulfhydryl-containing drugs, which stimulate the production of insulin autoantibodies. Among sulfhydryl-containing compounds, alpha lipoic acid (ALA) has recently emerged as a cause of IAS. After the first observations of ALA-induced IAS were reported in Japan in 2006, an increasing number of cases related to ALA administration have been described. An Italian group recently reported on six cases of IAS of which one was associated with HLA-DRB1*04:06 and the remaining five with HLA-DRB1*04:03. This suggests that the latter is potentially involved in the genetic susceptibility of people of European descent to IAS.

METHODS

Here, we describe two new cases of IAS in women that were triggered by ALA.

RESULTS

Both cases are associated with HLA-DRB1*04:03 and confirm the evidence that HLA-DRB1*04:03 rather than HLA-DRB1*04:06 is specifically related to IAS susceptibility in Europeans.

CONCLUSIONS

Case reports of ALA-induced hypoglycemic episodes highlight the need for greater care in prescribing ALA supplementation as well as the identification of specific and personalized therapeutic targets.

HLA-A*11:01 is associated with levetiracetam-induced psychiatric adverse events

Levetiracetam (LEV) is effective for focal and generalized epilepsy and is used worldwide because of its relatively few drug interactions and favorable tolerability. However, some psychiatric adverse events (PAEs) have been reported, resulting in drug withdrawal. The pathophysiology of LEV-induced PAE has not yet been elucidated. In this study, we investigated the relationship between PAEs and human leukocyte antigen (HLA) genes. Eleven epilepsy patients, who developed PAEs after the administration of LEV and spontaneously improved after drug withdrawal, were enrolled retrospectively. Genomic DNA from the peripheral blood was extracted, and four-digit allele genotyping of HLA genes was performed. The genotype frequencies of HLA genes were compared to those of 80 patients in which LEV was well tolerated, as well as to 485 individuals from the general Korean population. The frequency of the HLA-A*1101 allele was significantly higher in the LEV-induced PAEs group compared to both the LEV-tolerant group (p = 0.021, OR 4.80, 95% CI 1.30-17.74) and the general Korean population (p = 0.015, OR 4.62, 95% CI 1.38-15.45). This study is the first attempt at investigating the relationship between the HLA system and LEV-induced PAE. The results of this study suggest that the HLA-A*1101 allele could be a risk factor for the development of PAEs.

Association between HLA alleles and lamotrigine-induced cutaneous adverse drug reactions in Asian populations: A meta-analysis

PURPOSE

The aim of this study was to assess the association between human leukocyte antigen (HLA) variants and lamotrigine (LTG)-induced cutaneous adverse drug reactions (cARDs).

METHODS

A comprehensive literature search was conducted on the relationship of HLA alleles with LTG-induced cADRs in Asian populations, through PubMed, Embase, and Cochrane Library. The last search was in February 2018. The pooled odds ratio (OR) with 95% confidence interval (95% CI) was used to access the strength of the association between an HLA allele and LTG-induced cADRs.

RESULTS

A total of 11 studies met the inclusion criteria and were enrolled in our meta- analysis, which were based on Chinese, Korean, and Thai populations. Among these populations, we observed that HLA-B*1502 is a risk allele for LTG-induced Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) in Chinese populations (pooled OR 2.4, 95% CI: 1.20-4.78, P = 0.01), HLA-A*2402 was found to be a significant risk allele for both SJS/TEN (pooled OR 3.50, 95% CI: 1.61-7.59, P = 0.002) and maculopapular eruption (MPE) (pooled OR 2.14, 95% CI: 1.10-4.16, P = 0.03), and HLA-B*3303 was considered to be a protective marker for MPE in Chinese and Korean populations (pooled OR 0.2, 95% CI 0.06-0.64, P = 0.007).

CONCLUSIONS

In Asian populations, HLA-B*1502 is a risk factor for LTG-induced bullous lesions such as SJS/TEN in Chinese populations, and HLA-A*2402 is associated with the susceptibility to either SJS/TEN or MPE. HLA-A*3303 is a protective allele against LTG-induced MPE in Chinese and Korean populations.

Genetic Association in the HLA Region

The MHC/HLA region has been consistently associated with a large number of complex traits, including but not limited to, most immune-mediated ones. Efforts to pinpoint drivers of this commonly encountered association peak at the short arm of chromosome 6, however, have been challenging, owing to the high density of genes and the long and extended linkage disequilibrium that are characteristic of this region.The development of methods to impute classical HLA alleles and amino acids from SNP genotyping data has offered an important additional layer of information to the investigators seeking to fine map the signal in the region. As a result, imputation-aided association analyses are now typically employed to shed light on the relationship of this locus with disease susceptibility and response to drugs.In this chapter we discuss how the signal in the HLA region can be interrogated in practice, from performing the imputation to understanding its output and to incorporating it into downstream analysis. In addition, we recount some of the analytical approaches that are commonly used and suggest ways in which the findings from such imputation-aided analyses can be interpreted.

The HLA-A*31:01 allele: influence on carbamazepine treatment

Carbamazepine (CBZ) is an effective anticonvulsant that can sometimes cause hypersensitivity reactions that vary in frequency and severity. Strong associations have been reported between specific human leukocyte antigen (HLA) alleles and susceptibility to CBZ hypersensitivity reactions. Screening for HLA-B*15:02 is mandated in patients from South East Asia because of a strong association with Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). HLA-A*31:01 predisposes to multiple phenotypes of CBZ hypersensitivity including maculopapular exanthema, hypersensitivity syndrome, and SJS/TEN in a range of populations including Europeans, Japanese, South Koreans and Han Chinese, although the effect size varies between the different phenotypes and populations. Between 47 Caucasians and 67 Japanese patients would need to be tested for HLA-A*31:01 in order to avoid a single case of CBZ hypersensitivity. A cost-effectiveness study has demonstrated that HLA-A*31:01 screening would be cost-effective. Patient preference assessment has also revealed that patients prefer pharmacogenetic screening and prescription of alternative anticonvulsants compared to current standard of practice without pharmacogenetic testing. For patients who test positive for HLA-A*31:01, alternative treatments are available. When alternatives have failed or are unavailable, HLA-A*31:01 testing can alert clinicians to 1) patients who are at increased risk of CBZ hypersensitivity who can then be targeted for more intensive monitoring and 2) increase diagnostic certainty in cases where hypersensitivity has already occurred, so patients can be advised to avoid structurally related drugs in the future. On the basis of the current evidence, we would favor screening all patients for HLA-A*31:01 and HLA-B*15:02 prior to starting CBZ therapy.