Simplify the following text for a Grade 11 native English-speaking person.
Original: Although it is not mentioned in the DSM-IV , earlier theorists have proposed a personality disorder which has a combination of features from borderline personality disorder and Avoidant personality disorder , called `` avoidant-borderline mixed personality '' ( AvPD\/BPD ) .
Simplified: Avoidant personality disorder ( AvPD ) is a type of personality disorder and mental illness .