Genetic determinants of cocaine-associated agranulocytosis

Buxton et al. BMC Res Notes (2015) 8:240 DOI 10.1186/s13104-015-1219-4 Open Access RESEARCH ARTICLE Genetic determinants of cocaine‑associated agranulocytosis Jane A Buxton1,2*, John Omura2, Margot Kuo1, Colin Ross3, Despina Tzemis1, Roy Purssell4, Jennifer Gardy1,2 and Bruce Carleton3 Abstract Background: Drug-induced agranulocytosis is a recognized adverse drug event associated with serious infectious complications. Levamisole is an antihelminthic and immunomodulator withdrawn from North American markets in 2005 after reports of agranulocytosis. Previous studies of levamisole, suggest that the human leukocyte antigen (HLA)B27 confers a genetic predisposition to this adverse drug event. Since 2009, emergency room visits due to agranulocytosis in individuals consuming levamisole-adulterated crack-cocaine have increased. Methods: We performed a case–control study using a genotyping assay and novel gene chip to test the association between cocaine-associated agranulocytosis (CAA) and HLA-B27 and to identify pharmacokinetic and pharmacodynamic gene variants associated with the phenotype. Results: Fifty-one CAA cases were identified through a provincial physician reporting system between 2008 and 2011. We examined eight of these cases and 26 matched controls. Genotyping revealed a significant association between HLA-B27 and CAA (odds ratio [OR] 9.2, 95% confidence interval [CI], 1.54–54.6). We also observed a similar association with the HLA-B27 tag single nucleotide polymorphism rs4349859 (OR 9.2, 95% CI 1.5–54.6) and rs13202464 (OR 6.7, 95% CI 1.1–41). Further associations were identified with variants in the ARBCC12 (OR 10.0, 95% CI 2.7–36.8) and CYP11A1 (OR 7.4, 95% CI 2.1–26.6) genes, while a novel protective association was observed with variants in the ARDB1 gene (OR 0.06, 95% CI 0.007–0.46). Conclusions: We confirmed the association of HLA-B27 with CAA and identified additional susceptibility variants. Health care providers should inform people who are identified as having CAA that it is genetically determined and can recur with continued cocaine use. The severity of infections and subsequent hospitalization, and the risk of recurrence may prompt health-promoting behaviour changes of the affected individuals. These genetic associations warrant the attention of public health and knowledge translation efforts to highlight the implications for susceptibility to this severe adverse drug event. Keywords: Agranulocytosis, Levamisole, Cocaine, HLA-B27 antigen, Pharmacogenetics, Neutropenia Background Agranulocytosis is a recognized adverse drug event characterized by a decrease in peripheral neutrophil count to less than 500/µL (0.5 × 109/L) [1], with affected individuals at increased risk of infection, sepsis, and death [2]. Multiple drugs have been implicated as potential triggers of agranulocytosis, including levamisole [3]. Originally *Correspondence: 1 BC Center for Disease Control, 655 West 12th Avenue, Vancouver, BC V5Z 4R4, Canada Full list of author information is available at the end of the article formulated as a veterinary antihelminthic, levamisole was later used to treat autoimmune disorders including rheumatoid arthritis (RA) and as adjuvant chemotherapy for colon cancer. Agranulocytosis became a well-recognized complication of levamisole therapy, occurring in 2.5–13% of exposed patients [4]. These findings eventually led to its voluntary withdrawal from the US market in 1999 [5] and the Canadian market in 2005 [6], although levamisole continues to be used in veterinary medicine as an antihelminthic in the USA, Canada and South America [5, 6]. © 2015 Buxton et al. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Buxton et al. BMC Res Notes (2015) 8:240 In 2005, levamisole was first identified as a cocaine adulterant [7] and by July 2009 was found in as many as 69% of seized cocaine samples tested by the United States Drug Enforcement Administration [8]. Reports of agranulocytosis in individuals using levamisole-adulterated cocaine first emerged in 2009 from Alberta and British Columbia (BC), Canada [6, 9] and New Mexico, USA [8] with later reports from other parts of Canada and the United States demonstrating a spectrum of pathology including cutaneous vasculopathy [10–13]. Relapse is common with approximately half of patients experiencing more than one episode of agranulocytosis associated with return to cocaine use [6]. The mechanism by which levamisole induces agranulocytosis is thought to be immune-mediated. While no reported cases of levamisole-induced agranulocytosis could be identified from the period when the drug was used primarily as an antihelminthic agent, case reports emerged when its treatment profile broadened to include RA in the late 1970s and early 1980s [14, 15]. Studies of affected RA patients demonstrated an association between human leukocyte antigen (HLA)-B27 positivity and levamisole toxicity [16–18]. Initial findings amongst cases of cocaine-associated agranulocytosis (CAA) suggest a similar association with HLA-B27 [2, 15]. We performed a case–control study to confirm the association between CAA and HLA-B27 and used a novel SNP genotyping assay to identify genetic markers for CAA. Methods Setting and study design We conducted a case–control study of CAA using the British Columbia Centre for Disease Control’s (BCCDC) voluntary physician reporting system that communicated with emergency department staff and other health professionals through provincial medical health officers. Approval was obtained from the University of British Columbia Clinical Research Ethics Board. Study participants Cocaine-associated agranulocytosis cases, defined as individuals with a neutrophil count ≤0.5 per 109/L and laboratory confirmation or self-reported cocaine use at the time of diagnosis, were identified both retrospectively from 2008 and prospectively from case reports provided between January 2009 and October 2011. Case reports included patient demographics, clinical information, and past medical history [6, 19]. Eligible cases were recruited through study invitation letters distributed by the reporting physician with an invitation to contact a research team member for enrollment. This study employed a 1:3 case– control ratio; controls were recruited using case-based Page 2 of 6 snowball sampling (i.e. cases gave study information to people they knew to invite them to contact the research team if they were interested (...truncated)