Conversely the effect of the presence of a particular variant of the DAT1 gene may “cancel” the effect of another variant of the HTR1A gene: for example the odds of BPD occurrence in patients with the 9,10 variants of the DAT1 gene, and the C,G variants of the HTR1A gene are within 18% of the odds of BPD occurrence in a patient with the reference categories of the 10,10 variant of the DAT1 gene and the G,G variant of the HTR1A gene. This evidence concerns the gene HTR1A and Borderline personality disorder.