There is no one trigger of paranoid personality disorder is not known, as with most psychiatric problems, the causes of paranoid personality disorder may also include an interplay of biological and psychological factors.  It has also been seen that paranoid personality disorder is more common in people who have close relatives or family members with schizophrenia and/or delusional disorder which suggests a genetic link, but at the same time, it could also be that the person has internalized some of that suspicious behavior and thinking processes, so it needs to be studied further.