Dissociation, including depersonilization is a part of PTSD. Even severe depersonalization would not be considered a seperate disorder if you have already been diagnosed with PTSD, because it is better explained by the PTSD. DID develops in early childhood (almost always by age 3), so no, nothing leads into DID. It is very common, however, for people who have DID to be misdiagnosed numerous times with other psych and medical problems before the DID is correctly identified.