Acute lymphoblastic leukaemia (ALL) has posed challenges to the clinician due to variable patients' responses and late diagnosis. With the advance in metabolomics, early detection and personalised treatment are possible.
Genetic polymorphisms of thiopurine S-methyltransferase (TPMT) and inosine triphosphate pyrophosphohydrolase (ITPA 94C>A) contribute to variable responses, including fatal adverse effects, among subjects treated with 6-mercaptopurine (6-MP). Our objectives were to investigate the distribution of specific TPMT and ITPA genotypes in healthy subjects and patients with acute lymphoblastic leukaemia (ALL) from the three main ethnic groups (Malays, Chinese and Indians) in Malaysia and the association of the polymorphisms with adverse effects of 6-MP.
Matched MeSH terms: 6-Mercaptopurine/therapeutic use
Prolonged exposure to thiopurines (eg, mercaptopurine [MP]) is essential for curative therapy in acute lymphoblastic leukemia (ALL), but is also associated with frequent dose-limiting hematopoietic toxicities, which is partly explained by inherited genetic polymorphisms in drug metabolizing enzymes (eg, TPMT). Recently, our group and others identified germ line genetic variants in NUDT15 as another major cause of thiopurine-related myelosuppression, particularly in Asian and Hispanic people. In this article, we describe 3 novel NUDT15 coding variants (p.R34T, p.K35E, and p.G17_V18del) in 5 children with ALL enrolled in frontline protocols in Singapore, Taiwan, and at St. Jude Children's Research Hospital. Patients carrying these variants experienced significant toxicity and reduced tolerance to MP across treatment protocols. Functionally, all 3 variants led to partial to complete loss of NUDT15 nucleotide diphosphatase activity and negatively influenced protein stability. In particular, the p.G17_V18del variant protein showed extremely low thermostability and was completely void of catalytic activity, thus likely to confer a high risk of thiopurine intolerance. This in-frame deletion was only seen in African and European patients, and is the first NUDT15 risk variant identified in non-Asian, non-Hispanic populations. In conclusion, we discovered 3 novel loss-of-function variants in NUDT15 associated with MP toxicity, enabling more comprehensive pharmacogenetics-based thiopurine dose adjustments across diverse populations.