Original article 59 Gene variations in the cholecystokinin system in patients with panic disorder Pernille Koefoed a,b,c , David P. Woldbye a,c , Thomas O. Hansen b , Elsebeth S. Hansen c,e , Gitte M. Knudsen d , Tom G. Bolwig c and Jens F. Rehfeld b Objectives Panic disorder (PD) is a common psychiatric disease occurring more frequently in women than men. Multiple common and/or rare variants in the genome contribute to the complex etiology of the disorder. The neuropeptide cholecystokinin (CCK) and its receptors (the CCK system) have been suggested to be involved in the pathogenesis of PD. Methods We examined the promoter, exon, and exon–intron boundaries of the genes encoding CCK and its receptors (CCKAR and CCKBR) for variations in 187 patients with PD and 277 screened control individuals. Up to 1342 additional healthy population controls were examined for some of the variations. One CCK gene intron variation was analyzed for alternative splicing using an exon-trapping assay. Results The promoter variant ( – 36C > T; rs1799923) and an intron 1 polymorphism (IVS1-7C > G; rs754635) in the CCK gene were found to protect against PD (P < 0.05). The intron 1 variation did not seem to alter the splicing of the gene. None of the other variations found were associated with PD, but a 2-marker haplotype (rs1800855/ rs1800857) in the CCKAR gene protected women against PD (P = 0.004). In addition, we found two novel rare missense variations in the CCKBR gene (Lys329Asn and Pro446Leu) in two and one patient, respectively. Conclusion The results suggest that the CCK system may play a role in the pathogenesis of PD, with susceptibility alleles both protecting and contributing to the disease. Both common and rare variants seem to be involved. The involvement of the CCK system may also contribute to the increased prevalence of PD in women. Psychiatr Genet 20:59–64  c 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins. Psychiatric Genetics 2010, 20:59–64 Keywords: case–control study, exon-trapping, panic disorder, sequency a Laboratory for Neuropsychiatry, Department of Neuroscience and Pharmacology, b Department of Clinical Biochemistry, c Centre of Psychiatry, d Center for Integrated Molecular Brain Imaging, Rigshospitalet, University of Copenhagen and e Oringe, Psychiatry Vordingborg, Denmark Correspondence to Pernille Koefoed, PhD, Laboratory for Neuropsychiatry, Department of Neuroscience and Pharmacology, University of Copenhagen, O-6102, Blegdamsvej 9, Copenhagen 2100, Denmark Tel: + 45 3545 6115; fax: + 45 3539 3546; e-mail: pkoefoed@sund.ku.dk Received 21 April 2009 Revised 18 August 2009 Accepted 24 August 2009 Introduction Panic disorder (PD) is a common psychiatric disease with a lifetime prevalence of 3.5% in the total population, 5% of women and 2% of men (Kessler et al., 1994). Data from twin and family studies strongly indicate the involvement of genetic factors in the disorder (Smoller et al., 2008). The genetic susceptibility for developing PD is believed to be determined by contributions from risk alleles at multiple loci, together with genotype-by-environment interactions (including sex) and risk behaviors. It is de- bated whether these causal multiple variants correspond to multiple rare loci or, conversely, are common polymor- phisms (Chakravarti, 1999; McClellan et al., 2007). These two models are not mutually exclusive. However, most studies of susceptibility in genetics focus on analysis of ‘common variants’ (Goldstein and Chikhi, 2002). An association between cholecystokinin (CCK) and PD was observed in 1979 by one of us, who noted that an intravenous bolus injection of CCK-4 (the bioactive C-terminus of CCK peptides) precipitated panic-like attacks in normal controls (Rehfeld, 1992, 2000). It is now well established that exogenous CCK-4 provokes panic attacks both in normal controls and in patients with PD (DeMotigny, 1989). PD patients, however, seem more sensitive to CCK-4 than normal controls (Bradwejn et al., 1991). The reproducible panicogenic effect of CCK-4 is still used to investigate PD (Eser et al., 2007; Maron et al., 2008). Wang et al. (1998) found a polymorphism located in the CCK gene promoter region ( – 36C > T) that seemed to be associated with PD; however, subsequent studies could not confirm this result (Kennedy et al., 1999; Hamilton et al., 2001; Ho ¨sing et al., 2004; Maron et al., 2005). An association with PD has also been found for variations in the CCK-B receptor (CCKBR) gene (Kennedy et al., 1999; Binkley et al., 2001; Grataco `s et al., 2009). Again, other studies did not support these findings (Kato et al., 1996; Hamilton et al., 2001; Hattori et al., 2001; Yamada et al., 2001). Miyasaka et al. (2004) found an association with a 2-marker haplotype located in the 0955-8829  c 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI: 10.1097/YPG.0b013e32833511a8 Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.