The Frequency of Thiopurine Methyltransferase Polymorphism in Systemic Lupus Erythematosus Patients and Its Association With Azathioprine-Induced Adverse Effects

ABSTRACT Background: Thiopurine S-methyltransferase (TPMT) is the rate-limiting enzyme for azathioprine (AZA) metabolism. Polymorphisms of this gene induce adverse effects of AZA. AZA is widely used as an immunosuppressant agent for the remission maintenance of Systemic Lupus Erythematosus (SLE). Objective: To study the frequency of TPMT polymorphism in SLE patients. Methods and Materials: This observational nested case control study was conducted in the department of Rheumatology (BMU) and Pharmacokinetics and Pharmacogenetics Laboratory, department of Pharmacy, Dhaka University (DU), Dhaka, from July 2014 to January 2016. 348 (aged 18-65 years) SLE patients were enrolled, 11 were excluded, and 337 were included. Among them, 120 patients took AZA. All patients gave informed written consent. We included the patient who fulfilled ACR criteria for SLE and excluded the following patients: pregnant woman, taking another myelosuppressive or experimental drug, recent blood transfusion, and unwilling patient. A five ml blood sample was collected from each patient and analyzed for a genetic study. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique was used to detect the gene. The individual patient's disease activity was evaluated using the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI). The chi-square test was used to compare the frequency of alleles in SEE patients who received AZA. Results: A total of 348 SLE patients accepted the request to participate. DNA was not isolated from 11 patients, and they were excluded from this study. The remaining 337 patients were evaluated. The patients were divided into two groups: one was the AZA group and the other was the non-AZA group. In the AZA group, there were 120 patients, and in the non-AZA group, there were 217 patients. Nine patients of the AZA group were not included, and they were recorded as drop-out patients because they did not complete the follow-up visits. Mean age in the AZA group was 28.41±9.5 years and in the non-AZA group27.27±8.6 years. Mean weight in the AZA group was 53.2±6.5 kg, and in the non-AZA group was 53.01±6.8. Male patients were 13 (3.35%), and female patients were 324 (96.65%). In this study 12 patients TPMT polymorphism and the frequency was 3.56%. Among the 12 polymorphism patients a had TPMT3C mutant allele. There was no TPMT3A and TPMT2 mutant alleles found this study population. Total 10 patients developed myelosuppression. Among them (60%) had TPMT polymorphism and 4 (40%) had no TPMT polymorphism. In AZA group 7 patients had TPMT polymorphism, 6 (85.7%) patients developed myelosuppression and 1 (14.3%) patient did not develop it (myelosuppression). In AZA group was 53.2±6.5 kg and in non-AZA group was 53.01±6.3. Male patients were 13 (3.35%) and female patients were 324 (96.65%). In this study 12 patients TPMT polymorphism and the frequency was 3.56%. Among the 12 polymorphism patients all had TPMT3C mutant allele. There was no TPMT3A and TPMT2 mutant alleles found in this study population. Total 10 patients developed myelosuppression. Among them 6 (60%) had TPMT polymorphism and 4 (40%) had no TPMT polymorphism. In AZA group 7 patients had TPMT polymorphism, 6 (85.7%) patients developed myelosuppression and I (14.3%) patient did not develop it (myelosuppression). In myelosuppressed patients all of them developed anaemia and leucopoenia. Seven of the 10 patients developed thrombocytopenia and pancytopenia. A total of 16 (14.44%) patients developed AZA-induced adverse effects (including myelosuppression). Two patients developed hepatotoxicity who had TPMT genetic polymorphism, but the rest of the nonhematological adverse effects developed in patients without the genetic polymorphism.

Conclusion: The frequency of TPMT polymorphism in this series of Bangladeshi SLE patients is 3.56%. Most of the patients with TPMT gene polymorphism developed AZA-induced myelosuppression. The hematological adverse effects of AZA were present both in patients with and without the genetic polymorphism