Investigation of cholecystokinin system genes in panic disorder

There is evidence for the role of the cholecystokinin (CCK) neurotransmitter system in the neurobiology of panic disorder (PD).(1) The CCK receptor agonist, CCK-tetrapeptide (CCK-4) fulfills criteria for a panicogenic agent(1) and there is evidence that PD might be associated with an abnormal function of the CCK system. For example, PD patients show an enhanced sensitivity to CCK-4 and exhibit lower CSF and lymphocyte CCK concentration as compared to healthy controls (reviewed by Bradwejn et al.(2)). Also, untreated PD patients display an increased CCK-4-induced intracellular Ca2+ mobilization in T cells relative to treated PD, depression and schizophrenia.(3) The CCK receptors have been classified into two subtypes: CCK-A and CCK-B. We report here a study of polymorphisms in the CCK pre-pro hormone gene (CCK), CCK-AR, and CCK-BR in DSM-IV panic patients (n = 99) vs controls matched for gender and ethnicity. The CCK polymorphism revealed no association with PD. We identified a new polymorphism for the CCK-A receptor gene, and tested it in our sample, with negative results. A single nucleotide polymorphism has been found in the coding region of the CCK-B receptor gene(4) (CCK-BR) and D Collier (personal communication) identified a highly polymorphic dinucleotide (CT), microsatellite in the 5' regulatory region. For the CCK-B receptor gene polymorphism, PD patients showed a significant association. Our genetic dissection of the CCK system thus far suggests that the CCK-B receptor gene variation may contribute to the neurobiology of panic disorder.