In contrast to Fkpb5 and SLC6A4, carriers of the 9R allele of the dopamine transporter gene SLC6A3 were at greater risk of developing PTSD compared to 10R/10R allele carriers irrespective of environmental factors (Chang et al., 2012), highlighting the independent contribution of certain genes and the need to consider environmental interactions on a gene-by-gene basis. Here, SLC6A4 is linked to post-traumatic stress disorder.