Personality refers to the innate and enduring characteristics that influence an individual’s attitudes, behaviours, and experience of themselves, others, and the world. Historically, personality disorders were conceptualised as enduring and pervasive disturbance in an individual’s patterns of thinking, feelings, and behaviours. This disturbance results in significant disturbance in their psychosocial functioning and interpersonal relationships The diagnosis of personality disorders in people with intellectual disability can be a contentious issue. The chapter presents an overview of the condition, the treatments with medication available, and their relevance.

Other categories of personality disorders, apart from borderline personality disorder are encountered in clinical practice and these are described and named in DSM-5 but not in ICD-11. The clinical features and diagnostic criteria of all these types are reviewed here. They are grouped into three clusters: Cluster A, the eccentric PDs – which include paranoid, schizoid and schizotypal PDs – and Cluster B, the dramatic group. The most important of these is antisocial personality disorder as well as borderline and histrionic PDs. Cluster C, which are the avoidant or fearful PDs, include avoidant, dependent and obsessive-compulsive types.

Also included in this chapter are a category of conditions known as ’impulse disorders’, where subjects experience an impulse to commit some action which may give them pleasure and are said to be ego-syntonic, yet result in distress to the individual or harm to others. These include gambling, gaming disorder, intermittent explosive disorder, kleptomania and pyromania.

In the DSM-5 main section for clinical diagnoses, psychopathology in Cluster C (Anxious-Fearful) is represented by three personality disorders: Avoidant, Dependent, and Obsessive-Compulsive. However, characterization of persistent anxious-fearful psychopathology has varied historically, and it appears that the cluster formation may not be retained with the next iteration of personality disorder diagnoses. This chapter examines the historical development of anxious-fearful personality disorders, and examines the different ways that associated symptoms and problems have been characterized and grouped to elucidate core features in order to clarify visions looking forward. There is an emphasis on avoidant behaviors, when describing the clinical manifestation of these personality disorders, and it is suggested that focusing on mechanisms for this kind of personality pathology, as well as explicitly addressing the issue of grain size, would enhance continuing efforts to improve diagnostic conceptualizations of personality pathology involving anxiety, fear, and avoidance.

This rejoinder responds to commentaries offered by Cain (this volume) and Arntz (this volume). The authors reiterate their view that incorporating mechanisms into research will open new pathways for understanding the nature of anxious fearful personality pathology and for improving diagnosis. They agree with and value the interpersonal theory for better understanding personality disorders, and for guiding treatment. They further argue that particular attention be paid to grain size in the study and conceptualization of anxious fearful personality pathology.