Association study between casein kinase 1 epsilon gene and methamphetamine dependence.

Casein kinase 1 epsilon (CKIepsilon) is a component of the DARPP-32 in second-messenger pathway. CKIepsilon phosphorylates and activates DARPP-32, a key molecule in various complex signaling pathways, including dopamine and glutamine signaling, which have both been demonstrated to be main pathways in substance dependence. A recent clinical study showed that rs135745, a noncoding single nucleotide polymorphism of the 3'-untranslated region of the CSNK1E gene, was associated with the intensity of the subjective response to an oral amphetamine dose in normal volunteers. Differences in sensitivity to the drug should affect development of dependence to it. Hence, we genotyped rs135745 of the CSNK1E (MIM 600863) gene in 215 patients with methamphetamine dependence and 274 age- and gender-matched normal controls. No significant differences in genotype and allele frequencies were observed between the patients with methamphetamine dependence and controls. There was also no significant association between rs135745 and the clinical characteristics of methamphetamine dependence and co-morbid methamphetamine psychosis (e.g., age of first consumption, latency of psychosis, prognosis of psychosis after therapy, spontaneous relapse of psychotic symptoms, and poly-substance abuse status). The present findings suggest that having a genetic variant of the CSNK1E gene did not affect susceptibility to methamphetamine dependence or psychosis, at least in a Japanese population.