Clinical Utility of HLA-B*58:01 Genotyping to Prevent Allopurinol-Induced SJS/TEN

Abstract

Purpose: A 28-year-old male reported to our hospital with Stevens–Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) overlap syndrome that developed as an adverse drug reaction (ADR) to allopurinol. HLA-B*58:01 allele is associated with an increased risk of developing allopurinol-induced SJS/TEN. Methods: Genomic DNA was extracted from peripheral blood leukocytes. DNA sequencing was done using SANGER sequencing method. Results: Pharmacogenetic testing results revealed positive for HLA-B*58:01 allele. Symptoms of the patient receded after allopurinol withdrawal. Conclusion: The thrust of personalized therapy is from decoding the individual specific genetic variations astutely for better therapeutic outcomes such as reducing the ADRs. Pharmacogenetic testing is emerging as a safe, fast, and economic screening tool for personalized therapy by preventing ADRs. Pharmacogenetic HLA-B*58:01 allele testing before allopurinol administration could significantly reduce the incidence of SJS/TEN and associated mortalities/morbidities and thereby represent a potential cost-effective intervention.

Introduction

Stevens–Johnson Syndrome (SJS) and its severe form, toxic epidermal necrolysis (TEN), are rare but potentially fatal epidermolytic adverse cutaneous drug reactions that are considered medical emergencies.^1,2 SJS involves epidermal detachment of <10% of the body surface area whereas TEN involves epidermal detachment of >10% of body surface area. SJS/TEN overlap syndrome involves epidermal detachment of 10% to 30% of the body surface area and widespread purpuric macules or flat atypical targets. ³ A global population-based study had estimated the incidence of SJS and TEN to be 1.0 to 6.0 per million and 0.4 to 1.2 per million, respectively. ⁴ Asian patients have been estimated to possess a two-fold risk of developing SJS/TEN compared to Caucasian patients. ⁵ Medications such as antiepileptic drugs, antibiotics, and uric acid lowering agents, chemical exposures, mycoplasma pneumonia, viral infections, and immunizations have been implicated as potential causes for the development of SJS/TEN.^6,7 Allopurinol is considered the leading causative drug for the development of SJS/TEN in many countries.^1,8

SJS/TEN is a severe immune mediated or Type B adverse drug reaction (ADR) with a high mortality rate. ⁹ The risk of developing SJS/TEN is increased in patients who carry specific class I human leukocyte antigen (HLA) alleles. ¹⁰ The HLA-B gene is a part of the class I HLA group. ¹¹ The pathogenic mechanism of drug-induced SJS/TEN involves the possible interaction of the drug with the HLA protein present on the keratinocytes which induces CD8⁺ cytotoxic T-cells. Drug-specific CD8⁺ cytotoxic T-cells accumulate within blisters and release perforin and granzyme B that causes keratinocytes death. Keratinocytes death is also accounted by the secretion of granulysin by CD8⁺ T-cells, natural killer (NK) cells, and natural killer T (NKT) cells in the process. ¹² Among various genetic associations investigated, the human leukocyte antigen gene HLA-B*58:01 allele has emerged to be significantly associated with an increased risk of developing allopurinol-induced SJS/TEN.^13,14 Since HLA-B*58:01 allele is codominant, an individual possessing even a single copy of the allele is at increased risk for developing allopurinol-induced SJS/TEN. ¹⁵ Here we report the case of a 28-year-old South Indian male who presented to our hospital with SJS/TEN overlap syndrome and found to have HLA-B*58:01 allele upon HLA allele typing. This is the first pharmacogenetic study describing allopurinol-induced SJS/TEN in a native Indian patient.

Case Report

A 28-year-old South Indian male presented in our medicine department with a history of generalized skin rash for 7 weeks which was resolving latterly. The patient is employed for 6 months every year onshore on a merchant ship. He experienced pain in the medial aspect of the leg and visited a local orthopedic doctor for a consultation, where he was diagnosed with gouty arthritis and was prescribed allopurinol 300 mg/day for 7 days, followed by 300 mg/day for 20 days, and 100 mg/day for 6 months. One week after initiation of allopurinol therapy, he boarded the ship for duty.

On the 13th day of allopurinol intake, patient started experiencing throat pain which lasted for 5 days. On the 20th day, the patient noticed uniform erythematous rashes on his chest and stomach (Figure 1a) with slight itching. He immediately stopped taking allopurinol. On the 23rd day, crusting, discharge, puffiness, and itching in the eye were observed (Figure 1b). On the 24th day, the rashes spread to his face, hands, and back. The patient relayed his condition on the phone to the physician offshore. On suspecting mumps, he was prescribed by the onboard physician with paracetamol 325 mg + ibuprofen 400 mg tablet (3 days), ranitidine 150 mg capsule (3 days), amoxicillin capsule 500 mg (5 days), and multivitamin tablet (5 days). The patient was isolated in a clean room in the ship and was orally hydrated with water regularly. On the 25th day, the rashes on the periorbital region and chest turned to small blisters and the formation of bullae was observed on the lower abdomen (Figure 1c). On the 31st day, the sloughing of the skin around the periorbital area and bullae was observed (Figure 1d and 1e). All the dermatological symptoms started slowly resolving from the 32nd day (Figure 1f: 39th day). The patient visited the medicine department of our hospital on the 47th day. According to clinical evaluation and patient’s description of events with photographs, rashes and decantation of skin were seen over 68% and 13.5% of the body surface area, respectively, thereby classifying the case as SJS/TEN overlap syndrome. All the relevant laboratory evaluations of hematological, serum urea, serum creatinine, and C-reactive protein (CRP) were found to be normal. The patient was referred to the dermatology department and since the symptoms were receding, the patient was not prescribed any medications for the management of SJS/TEN.

Figure 1.

(a-f) Showing the course of dermatological manifestations of SJS/TEN overlap syndrome.

The patient had no known history of any allergy-related to food or drug and long-term use of drugs. Currently, patient is not experiencing any pain in the leg and hence is not on any medications for the treatment of gout. Causality assessment of the ADR using Naranjo adverse drug reaction probability scale (Score = 5) and World Health Organization–Uppsala Monitoring Center (WHO–UMC) causality system showed probable correlation with the adverse reaction (SJS/TEN).

HLA-B*58:01 genotyping: Genomic DNA was extracted from peripheral blood leukocytes by a silica-based method. DNA was quantitated on nanodrop spectrophotometer. PCR amplification was done by using the forward primer: 5′-GGCGGGGGCGCAGGACCTGA-3′ and reverse primer: 5′-GGAGGCCATCCCCGGCGACCTAT-3′. The gel was cut and kept at −20°C. The gel was chopped, phenol (pH: 7.4, 400 µL) was added to the sample and kept at −80°C overnight. DNA sequencing was done using SANGER sequencing method. The DNA sequence was then blasted with the National Center for Biotechnology Information (NCBI) nucleotide blast and showed 100% matching to HLA-B*58:01 (Supplemental File 1). The raw sequence data of HLA-B*58:01 using forward and reverse primers are attached with Supplemental Files 2 and 3, respectively.

Discussion

Generally, allopurinol-induced SJS/TEN occurs within weeks or a few months of initiating treatment. As per Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines, allopurinol use is contraindicated in patients who have tested positive for HLA-B*58:01 allele on account of the risk for developing SJS/TEN. ¹⁶ Pharmacogenetic testing for HLA-B*58:01 allele prior to initiation of allopurinol therapy could be highly beneficial for high-risk groups like the Asian population. ¹⁷ Clinical genotyping test is available for the detection of HLA-B*58:01 allele. The genotyping results are presented as either HLA-B*58:01 positive (at least one copy of HLA-B*58:01 is present) or as HLA-B*58:01 negative (no copies of HLA-B*58:01 are detected) with no intermediate genotype.^16,18 High predictive value of the HLA-B*58:01 allele testing has established the diagnostic utility among different populations. Our patient had tested positive for HLA-B*58:01 allele. ⁸ The expenditure cost incurred for performing HLA-B*58:01 allele testing for the patient was INR 4000 (~US$ 57). This cost appears to be relatively very low considering the pharmacoeconomics associated with SJS/TEN treatment and the risk of mortality rate associated with the condition. Hence HLA-B*58:01 allele testing as a prescreening strategy before allopurinol prescription in the Indian population could prove to be beneficial in terms of having better health and economic outcomes for the patients.

The 1000 Genome Project reported higher allelic frequencies of HLA-B*58:01 allele among the Asian Chinese population. ¹⁹ The allelic frequencies were reported to be 0.042 and 0.072 among the US South Asian Indians and native South Indian population respectively. ¹⁸ As the South Indian population is significantly underrepresented in current genomic studies and reference genome databases, the results from the GenomeAsia 100K is expected to provide a more comprehensive picture on the prevalence of HLA-B*58:01 allelic frequencies in the distinct ethnic groups of South Indian population and the assessing the necessity for incorporating HLA-B*58:01 allele genetic testing for allopurinol prescribing in the national guidelines.

Guidelines for allopurinol dosing in gout treatment suggest starting with a daily low dose of 50 to 100 mg, with 100 mg dose increments at approximately every 4 weeks to a maximum of 900 mg as necessary to control hyperuricemia. ²⁰ However, our patient was started on a dose of 300 mg, followed by tapering of dose. He started developing symptoms of SJS/TEN overlap after 2 weeks of initiation of allopurinol therapy and started to recover from the symptoms from 12 days after withdrawal of allopurinol.

To summarize, pharmacogenetic HLA-B*58:01 testing before allopurinol administration could be potential lifesaving and cost-effective intervention by preventing allopurinol-induced SJS/TEN. Translating the findings of pharmacogenetic testing for preventing SJS/TEN epitomizes the implementation of personalized therapy of allopurinol in clinical practice. Since current Indian guidelines does not have HLA-B*58:01 allele testing as a pre-screening strategy before allopurinol prescription initiation, careful dose consideration, close follow up, and genetic counseling should be performed for patients. Further large-scale research investigations in different ethnic groups of the diverse Indian population are necessary to assess the prevalence of HLA-B*58:01 allele and to delineate the exact role of the HLA-B*58:01 allele with allopurinol-induced SJS/TEN.