Association of an orexin 1 receptor 408Val variant with polydipsia-hyponatremia in schizophrenic subjects

Background Primary polydipsia is a common complication in patients with chronic psychoes, particularly schizophrenia. Disease pathogenesis is poorly understood, but one contributory factor is thought to be dopamine dysregulation caused by prolonged treatment with neuroleptics. Both angiotensin-converting enzyme (ACE) and orexin (hypocretin) signaling can modulate drinking behavior through interactions with the dopaminergic system. Methods: We performed association studies on the insertion/deletion (I/D) sequence polymorphism of ACE and single nucleotide polymorpbisms within the prepro-orexin (HCRT), orexin receptor 1 (HCRTR1), and orexin receptor 2 (HCRM) genes. Genotypes were determined by polymerase chain reaction amplification, followed by either electrophoretic separation or direct sequencing. Results. The ACE I/D polymorphism showed no association with polydipsic schizophrenia. Screening of the orexin signaling system detected a 408 isoleucine to valine mutation in HCRTR1 that showed significant genotypic association with polydipsic-byponatremic schizophrenia (p = .012). The accumulation of this mutation was most pronounced in polydipsic versus nonpolydipsic schizophrenia (p = .0002 and p = .008, for the respective genotypic and allelic associations). The calcium mobilization properties and the protein localization of mutant HCRTR1 seem to be unaltered. Conclusion: Our preliminary data suggest that mutation carriers might have an increased susceptibility to polydipsia through an undetermined mechanism.