Single nucleotide polymorphisms in the FKBP5 gene influence the risk of developing stress-related disorders, but the underlying processes are not fully understood. Animal models offer a possibility to investigate the influence of FKBP5 gene variants on the stress response system. For the last twenty years, we have known that vulnerability or resilience to early life stress is modulated by genetics; individuals carrying certain alleles of certain genes are more or less likely to present stress-associated pathologies than others1,2. In a new study, Nold and colleagues3 used humanized mice to investigate the effects of genetic and environmental factors on stress responses.