Serotonin transporter polymorphisms and adverse effects with fluoxetine treatment

Background The short (S) allele of the serotonin transporter gene-linked polymorphic region (5HTTLPR) has been associated with poorer antidepressant response in major depressive disorder (MDD) and with antidepressant-induced mania. This study investigated a possible association with treatment-emergent insomnia or agitation. Methods Thirty-six outpatients with MDD were genotyped at 5HTTLPR and treated with open-label fluoxetine up to 60 mg/day. Treatment-emergent adverse effects were assessed at each study visit. Results Of nine subjects homozygous for the “S” allele, seven (78%) developed new or worsening insomnia, versus 6 of 27 (22%) non-“S”-homozygous subjects (Fisher’s exact p = .005). Similarly, six of nine subjects homozygous for the “S” allele (67%) developed agitation, versus 2 of 27 (7%) of non-“S”-homozygous subjects (Fisher’s exact p = .001). Conclusions The “S” allele of the 5HTTLPR may identify patients at risk for developing insomnia or agitation with fluoxetine treatment. This preliminary result requires confirmation in larger samples.