Molecular Psychiatry (2001) 6, 59–65  2001 Macmillan Publishers Ltd All rights reserved 1359-4184/01 $15.00 www.nature.com/mp ORIGINAL RESEARCH ARTICLE No association or linkage between polymorphisms in the genes encoding cholecystokinin and the cholecystokinin B receptor and panic disorder SP Hamilton 1 , SL Slager 1 , L Helleby 1 , GA Heiman 1 , DF Klein 1 , SE Hodge 1,2 , MM Weissman 1,3 , AJ Fyer 1 and JA Knowles 1,4 1 Department of Psychiatry, College of Physicians and Surgeons at Columbia University and the New York State Psychiatric Institute; 2 Division of Biostatistics; 3 Mailman School of Public Health, Columbia University; 4 Columbia Genome Center, College of Physicians and Surgeons at Columbia University Growing animal data implicate cholecystokinin in the regulation of anxiety, while human clini- cal research confirms the role of cholecystokinin in the provocation of panic attacks. Anti- panic medications suppress the ability of cholecystokinin to induce panic attacks, and may alter the expression of the cholecystokinin gene. Thus, there is increased interest in under- standing the molecular genetic component of these observations. Recent association studies using persons with panic disorder described some association between polymorphisms in the genes encoding cholecystokinin and the cholecystokinin B-receptor and panic disorder. In this study, we used a family-based design, employing 596 individuals in 70 panic disorder pedigrees, as well as 77 haplotype relative risk ‘triads’. Subjects were genotyped for two poly- morphisms: the polymorphic microsatellite marker in the CCK-BR locus using PCR-based genotyping and at a single nucleotide polymorphism in the CCK promoter using a fluor- escence polarization detection assay, and the data were analyzed for genetic association and linkage. Employing a variety of diagnostic and genetic models, linkage analysis produced no significant lod scores at either locus. Family-based tests of association, the haplotype-based haplotype relative risk statistic and the transmission disequilibrium test, were likewise non- significant. The results reported here provide little support for the role of these polymor- phisms in panic disorder. Molecular Psychiatry (2001) 6, 59–65. Keywords: candidate gene; fluorescence polarization; family-based Introduction It is estimated that between 1 and 3% of the population suffers from panic disorder during their lifetime. 1 Per- sons with this disorder suffer from recurrent panic attacks, experienced as spontaneous crescendo peaks of anxiety, with somatic and psychological symptoms, accompanied by anticipatory anxiety. A number of family studies show that first degree relatives of per- sons with panic disorder have a 2.6–19.5-fold relative risk of having panic disorder compared to controls, 2 with this risk being increased in families of probands with early onset 3 or with smothering symptoms. 4 A smaller number of twin studies have reported that heri- table factors contribute about 30–40% of the liability towards panic disorder. 5 Recent segregation analyses suggest that recessive and dominant modes of inherit- ance are equally likely, and that panic disorder is Correspondence: JA, Knowles, New York State Psychiatric Insti- tute, Unit No. 28, 1051 Riverside Drive, New York City, NY 10032, USA. E-mail: jak8columbia.edu Received 11 February 2000; revised 24 June 2000; accepted 7 July 2000 unlikely to have a simple Mendelian inheritance. 6,7 These genetic factors have been the focus of recent work employing genome-wide 8 and candidate gene strategies. 9–14 Although the psychobiology of panic disorder is a mystery, several lines of evidence underscore a developing understanding of the pathophysiology. First, the utility of medications in treating panic dis- order suggests the involvement of various neuro- transmitter systems, including noradrenergic and sero- toninergic circuits. Additional insight into the disorder has been gained from challenge studies, in which panic is provoked differentially in panic disorder patients when compared to normal controls after ingestion, inhalation, or injection of anxiogenic substances (see Bourin et al for review). 15 The peptide cholecystokinin (CCK) is one such panicogenic agent. Injection of a tetrapeptide (CCK-4) derived from the full CCK sequence induces panic attacks in normal controls 16 and in persons with panic disorder, 17 with persons with panic being much more sensitive than controls to the effects of CCK-4. 18 Likewise, agonists to the CCK-B receptor differentially induce panic in those with panic disorder when compared to controls. 19 Antagonists to