The prevalence of psychiatric disorders among patients with intellectual disability (ID) and low-functioning autism spectrum disorder (ASD) is higher than in the general population. The available reports on this comorbidity vary depending on the adopted methodologies, the size of the examined ID population, and the criteria used to diagnose mental disorders. Multiple factors contribute to the significantly different presentation of psychopathological symptoms and syndromes in people with ID and ASD compared to the general population, including cognitive and communicative impairments, developmental peculiarities, and neuro-autonomic vulnerability. Because they have a hard time conceptualizing and articulating their mental states, the diagnosis of their psychopathology must rely on firsthand observation of behaviors in the context of daily life as well as third-party accounts. As a result, diagnostic criteria designed for the general population are ineffective when used in these groups, so for them specific diagnostic procedures and instruments should be a significant determinant of psychiatric diagnosis validity.

People with intellectual disability may be subject to unfitness to plead proceedings in court due to the nature of their disability. In addition, people withintellectual disability in England and Wales are also subject to legislation such as the Mental Capacity Act 2005 and the Mental Health Act 1983 (as amended in 2007). This chapter explores issues with current fitness to practise proceedings for people with intellectual disability in relation to the Mental Capacity Act and the Mental Health Act, including the use of Sections 35 and 36.

The link between neurodevelopmental disorders and offending behaviour is examined in other chapters of this book. This chapter’s focus is on the comorbidity between neurodevelopmental conditions and psychiatric disorders, when a person with one or more neurodevelopmental condition develops additional mental health problems. Specifically, the impact of such comorbidity in the development and maintenance of offending behaviour is addressed. In doing so, the authors examine each of the major neurodevelopmental disorders (intellectual disability, autism spectrum disorder and attention deficit hyperactivity disorder separately in the light of up-to-date evidence for each condition. The importance of identifying the presence of comorbid psychiatric disorders, including substance use disorder, is highlighted as essential in the diagnostic evaluation of those with neurodevelopmental conditions presenting with offending behaviour.

The chapter provides an introduction to neurodevelopmental disorders and summarises recent advances in published research, focusing on the very early development and function of the human brain. The main influences on the current delivery and development of forensic healthcare services is set within the context of available policy and guidance, which is limited in part by the available research evidence to inform it. The book is divided into three sections. The first provides an overview with an introduction to individual disorders and covers aetiology, prevalence, comorbid mental disorder and relevant policy to date. The second section focuses on the clinical aspects of the range of disorders including screening, assessment, diagnosis, risk assessments and therapeutic approaches. The final section examines the pathways through the criminal justice system from police to court to disposal and addresses the specific aspect of fitness to plead or stand trial for those with neurodevelopmental disorders. This section also describes current relevant legislation within the UK as well as forensic services for those with such disorders from a national and international perspective.

The study of subthreshold neurodevelopmental disorders (STNDs) and the implications for future health, social and criminal justice services is in its infancy. Current research points towards increased vulnerability to a number of risk factors that are likely to impact both the individual and future service demand. Offenders who meet diagnostic criteria for a specific neurodevelopmental disorder are often shown to have more similarities than differences to offenders with STNDs. As well as communication and adaptive problems, similarities also include higher rates of mental disorder and increased vulnerability to suicide and self-harm. Within STNDs there exists a wide variation in presentation which may be atypical. The future study of STNDs requires a coordinated strategy and agreement as to a common definition using a dimensional approach.

This is the first book to bring together the evidence base from leading researchers and clinicians at international level on the forensic needs of people with neurodevelopmental disorders. We hope the readers will find the evidence presented in this book not only informative but a useful reference source for their day-to-day clinical practice. There are many themes running throughout the book but one key one is that people with neurodevelopmental disorders present to the forensic system as complex, with more than one health and social care need. Another theme is the challenge of how best to recognise people with neurodevelopmental disorders across the different parts of the criminal justice system, ensuring there is expertise to provide assessments early on in the journey of defendants. The availability of evidence-based treatments needs to be embedded across forensic settings including correctional settings, health facilities and community-based services.