© 2009 Nature America, Inc. All rights reserved. NATURE GENETICS ADVANCE ONLINE PUBLICATION 1 Cisplatin is a widely used and effective chemotherapeutic agent, although its use is restricted by the high incidence of irreversible ototoxicity associated with it 1 . In children, cisplatin ototoxicity is a serious and pervasive problem, affecting more than 60% of those receiving cisplatin 2–5 and compromising language and cognitive development. Candidate gene studies have previously reported associations of cisplatin ototoxicity with genetic variants in the genes encoding glutathione S-transferases and megalin 6–8 . We report association analyses for 220 drug-metabolism genes in genetic susceptibility to cisplatin-induced hearing loss in children. We genotyped 1,949 SNPs in these candidate genes in an initial cohort of 54 children treated in pediatric oncology units, with replication in a second cohort of 112 children recruited through a national surveillance network for adverse drug reactions in Canada. We identified genetic variants in TPMT (rs12201199, P value = 0.00022, OR = 17.0, 95% CI 2.3–125.9) and COMT (rs9332377, P value = 0.00018, OR = 5.5, 95% CI 1.9–15.9) associated with cisplatin-induced hearing loss in children. Cisplatin has been described as one of the most ototoxic drugs in clinical use, causing serious, permanent, bilateral hearing loss in 10–25% of adults receiving the drug, 50% of individuals receiving high doses (>400 mg/m 2 ) and 41–61% of children 2–5,9 . In children, the impact of hearing loss is most profound because even mild losses of hearing considerably increase a child’s risk of learning difficulties and social-emotional problems 4,10 . Cisplatin ototoxicity frequently leads to dose reduction and premature termination of cisplatin treatment, which may affect overall survival rates. There is substantial inter- individual variation in ototoxicity in individuals receiving similar doses of cisplatin; this has led to the hypothesis that some individuals have polymorphisms in genes encoding drug-metabolizing enzymes that render them especially susceptible to cisplatin ototoxicity 11 . A discovery cohort of 54 children treated in pediatric oncology units who received cisplatin therapy was recruited from the BC Children’s Hospital in Vancouver, British Columbia, Canada (Table 1). Children who suffered serious cisplatin-induced ototoxicity (n = 33) were defined by the development of grade 2–4 hearing impairment following cisplatin therapy using Cancer Therapy Evaluation Program, Common Terminology Criteria for Adverse Events (CTCAE) criteria, showing a hearing loss of >25 dB at frequencies of 4–8 kHz. In this cohort, 22 (40%) children on cisplatin treatment did not experience any sig- nificant hearing loss (CTCAE grade 0). To better differentiate between cisplatin ototoxicity and normal hearing, children with hearing loss defined as grade 1 (n = 4) were removed from the initial analysis. A second, independent replication cohort of 112 children treated in pediatric oncology units who received cisplatin chemotherapy was recruited from pediatric oncology units across Canada (Table 1). In this cohort, 73 (66%) children suffered serious (defined as grade 2–4) cisplatin-induced ototoxicity. In the replication and combined cohorts, male gender was moderately associated with ototoxicity (67% compared to 50% in females, P value = 0.042 overall) and fewer children with germ-cell tumors developed ototoxicity (6.6% versus 26.8%, P value = 0.0006 overall), although these differences did not show a similar trend in the discovery cohort. Study participants’ DNA samples were genotyped for 1,949 SNPs using an Illumina GoldenGate assay designed to capture the genetic variation in 220 key genes involved in the absorption, distribution, metabolism and elimination (ADME) of medications and their metabolites (Supplementary Table 1). We used a tiered analysis strat- egy to identify variants that were highly associated with cisplatin oto- toxicity in the initial discovery cohort (P < 0.01) and that remained highly associated in a second replication cohort (P < 0.01) 12 . The key Genetic variants in TPMT and COMT are associated with hearing loss in children receiving cisplatin chemotherapy Colin J D Ross 1,2,11 , Hagit Katzov-Eckert 1,2,11 , Marie-Pierre Dubé 3 , Beth Brooks 4 , S Rod Rassekh 5 , Amina Barhdadi 3 , Yassamin Feroz-Zada 3 , Henk Visscher 1,2 , Andrew M K Brown 3,6 , Michael J Rieder 7 , Paul C Rogers 5 , Michael S Phillips 3,6 , Bruce C Carleton 2,8,9 Michael R Hayden 1,2 & the CPNDS Consortium 10 1 Department of Medical Genetics, University of British Columbia, Centre for Molecular Medicine and Therapeutics, Vancouver, British Columbia, Canada. 2 Child and Family Research Institute, Children’s and Women’s Health Research Centre of British Columbia, Vancouver, British Columbia, Canada. 3 Montreal Heart Institute and Université de Montreal, Montreal, Quebec, Canada. 4 Audiology and Speech Pathology Department and 5 Department of Pediatrics, Division of Pediatric Hematology/Oncology/Bone and Marrow Transplant, British Columbia Children’s Hospital, Vancouver, British Columbia, Canada. 6 Montreal Heart Institute and Genome Québec Pharmacogenomics Centre, Montreal, Quebec, Canada. 7 Department of Paediatrics, Children’s Hospital at the London Health Sciences Centre, London, UK. 8 Faculty of Pharmaceutical Sciences and 9 Department of Paediatrics, Pharmaceutical Outcomes Programme, University of British Columbia, Vancouver, British Columbia, Canada. 10 A full list of members is provided in the Supplementary Note. 11 These authors contributed equally to this work. Correspondence should be addressed to M.R.H. (mrh@cmmt.ubc.ca). Received 15 May; accepted 1 October; published online 8 November 2009; doi:10.1038/ng.478 LETTERS