Rare genotype combination of the serotonin transporter gene associated with treatment response in severe personality disorder

The insertion deletion (ins/del) polymorphism of the serotonin transporter gene (5-HTTLPR) has been associated with several psychiatric phenotypes and antidepressant's response. We investigated, in a large cohort of 5,608 controls and subjects suffering from various psychiatric disorders, the frequency of haplotypes and corresponding genotypes combining the 5-HTTLPR and the other serotonin transporter promoter functional variant (rs25531). We showed that rs25531 lies 18bp 5' to the site where the 43bp (and not 44bp as previously described) ins/del defines the 14- and 16-repeat alleles. These polymorphisms should therefore be considered as four alleles instead of a triallelic unique locus. The very rare G-14/G-16 genotype was carried on by only three subjects. These are women with a history of suicide attempt with a psychiatric history strongly suggesting a borderline personality disorder. Two of them have shown a non-response to serotoninergic antidepressant. Interestingly, in one of them was observed a spectacular response after the introduction of bupropion. The genotyping droved our therapeutic approach, by preferring a dopaminergic over a serotoninergic agent. This study highlights the usefulness of studying very rare clinical cases as well as rare variants, in order to deal with the biological heterogeneity of spectral disorders.