Abstract: The present invention relates to methods and kits of determining whether a subject is susceptible to have a hyper-aggressive behaviour. In particular, the present invention relates to a method for determining whether a subject is susceptible to have a hyper-aggressive behaviour comprising the steps consisting of i) isolating the auto antibodies that bind to adrenocorticotropic hormone (ACTH) from a blood sample obtained from the subject, ii) determining the affinity of the isolated autoantibodies iii) comparing the affinity determined at step ii) with a predetermined reference value and iv) concluding that the subject is susceptible to have a hyper-aggressive behaviour when the affinity determined at step ii) is higher than the predetermined reference value.