The 5-HTTLPR polymorphism has also been associated with adverse responses in methamphetamine abusers. The 5-HTTLPR polymorphism was tested for association with prolonged methamphetamine-induced psychosis in a case-control study of methamphetamine abusers (Ezaki et al. 2008), utilizing the sample and methods described in the previous section (Ujike et al. 2003). SLC6A4 was chosen as a candidate gene for this phenotype based on previous neuroimaging findings from the same group showing that methamphetamine abusers had lower serotonin transporter density than non-abusers (Sekine et al. 2006). The lower expressing S allele was significantly associated with methamphetamine psychosis, and in particular with prolonged psychosis. Thus, the S allele (and the LG allele in the one instance where it was differentiated from the LA allele) appears to be associated with more intense acute and chronic responses to various different stimulants. Furthermore, it appears that the lower expressing alleles of both the dopamine and the serotonin transporters are associated with greater propensity to methamphetamine-induced psychosis.
