Histamine N-methyltransferase functional polymorphism: lack of association with schizophrenia.

Histamine is a central nervous system (CNS) neurotransmitter that has been implicated in the pathophysiology of schizophrenia. Histamine N-methyltransferase (HNMT) terminates the neurotransmitter actions of histamine in the mammalian CNS, and levels of HNMT activity in human tissues are controlled, in part, by inheritance. A common C314T polymorphism in the HNMT gene causes a Thr105Ile change in encoded amino acid. The T314 allele results in decreased levels of both HNMT enzyme activity and immunoreactive protein. There is also a polymorphic CA repeat in intron 5 of the HNMT gene. The frequencies of alleles for the functional C314T polymorphism and the polymorphic CA repeat were compared between 171 schizophrenia cases and 171 ethnically matched controls to test for possible disease association. No significant difference was found between the two groups in the frequency of the T314 allele in patients with schizophrenia and controls (0.068 vs. 0.078, respectively). Allele frequencies for the polymorphic HNMT CA repeat also failed to show significant differences between cases and matched controls.