Thr105Ile, a functional polymorphism of histamine N-methyltransferase, is associated with alcoholism in two independent populations.
BACKGROUND
Histamine is expressed in cortical and limbic areas that are involved in emotion and cognition and modulates these behaviors. H1 receptor antagonists are sedative. Histamine N-methyltransferase (HNMT) catalyzes the Ntau methylation of histamine, the sole pathway for termination of the neurotransmitter action of histamine in mammalian brain. A common and functionally significant polymorphism, a C314T transition in exon 4 of the HNMT gene results in a Thr105Ile substitution of the protein encoded. The Thr105 allele is associated with approximately 2-fold higher enzyme activity, leading to the prediction that it might be associated with diminished histamine levels, resulting in differences in anxiety, cognition, and sedation that play important roles in alcoholism. In two ethnically distinct populations, we tested whether the Thr105Ile polymorphism was associated with alcoholism and with harm avoidance, a dimensional measure of anxious personality.


METHODS
A 5' exonuclease assay (TaqMan) was used to genotype Thr105Ile in psychiatrically interviewed Finnish Caucasian (n = 218) and Plains American Indian (n = 186) alcoholics, along with ethnically matched, psychiatrically interviewed, controls (Finns: n = 313, Plains Indian: n = 140).


RESULTS
Ile105 allele frequencies were significantly lower in alcoholics compared with nonalcoholics in both populations (Finns: 0.12 vs. 0.17, chi(2) = 6, p = 0.015; Plains Indians: 0.03 vs. 0.08, chi(2) = 5, p = 0.023). Genotype distributions also differed significantly. In Finns, Ile105 showed borderline significance for an association with lower harm avoidance (p = 0.070) after correcting for alcoholism diagnosis.


CONCLUSIONS
Decreased levels of brain histamine consequent to the Thr105 allele may result in higher levels of anxiety and, as a consequence, vulnerability to alcoholism.
Oroszi
Gabor
G
Laboratory of Neurogenetics, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland, USA. goroszi@mail.nih.gov
Enoch
Mary-Anne
MA
Chun
Jeffrey
J
Virkkunen
Matti
M
Goldman
David
D
D000328:Adult; D000437:Alcoholism / Q000235:genetics* / Q000523:psychology; D000483:Alleles; D001007:Anxiety / Q000235:genetics / Q000523:psychology; D005260:Female; D005387:Finland / Q000453:epidemiology; D005787:Gene Frequency; D005838:Genotype; D006637:Histamine N-Methyltransferase / Q000235:genetics*; D006801:Humans; D007198:Indians, North American; D008297:Male; D010556:Personality Tests; D043264:Phosphodiesterase I / Q000235:genetics; D011110:Polymorphism, Genetic / Q000235:genetics; D011569:Psychiatric Status Rating Scales; D014481:United States / Q000453:epidemiology; D044465:White People
D006637:Histamine N-Methyltransferase; D043264:Phosphodiesterase I