Awareness of children with significant problems in intellectual development can be traced to antiquity but awareness of associated problems in mental health is a much more recent phenomenon. The increase in awareness in recent years can be related to several factors: greater inclusion of individuals with disabilities in the population, the need to support individuals of all ages in their communities, and increasing sophistication on the part of both researchers and clinicians. Sadly, and somewhat paradoxically, a diagnosis of intellectual disability in the more distant past often led to a presumption that such individuals were somehow protected from other problems – the phenomenon known as ‘diagnostic overshadowing’. However, research with this population began to suggest that rather the converse was true, with persons exhibiting milder intellectual disability having 4- to 5-fold increases in rates of associated psychiatric problems (Reiss & Szyszko, 1983). Awareness also began to increase regarding the difficulty of applying the usual models of psychiatric nosology, particularly in individuals with more severe intellectual disability (Fletcher et al, 2007).Other work began to note significant associations between certain syndromic forms of intellectual disability and specific mental disorders (Dykens & Hodapp, 2001). This volume provides an important overview and update of the current status of the field, and areas where more work is needed.

The opening chapters of this book provide a very helpful overview of basic issues and approaches to classifying intellectual disability and characterising behavioural phenotypes. The next section summarises comorbidity, with specific chapters on commonly associated conditions in general, and anxiety disorders in particular. Relevant disorders are highlighted including behavioural difficulties, problems associated with seizure disorders, and pharmacological management.

Part three of the volume focuses on autism and related conditions. This is an area where there has been a vast increase in research, although, unfortunately, problems in adolescents and adults have been much less frequently addressed. Chapter 8 provides a helpful overview, with other chapters focused more specifically on Asperger syndrome and on pharmacological management.

Interest in what is now recognized as the pervasive developmental disorders can be traced to the middle of the nineteenth century with the first descriptions of childhood “psychosis” (Volkmar, 1996). This interest stemmed from an increasing awareness of the importance of the factors of both experience and endowment in child development. Early descriptions of childhood “insanity” were followed by descriptions of childhood schizophrenia (DeSanctis, 1906). The latter term became synonymous with all forms of severe mental disorder in children. The particular genius of Leo Kanner was reflected in his description in 1943 of the syndrome of infantile autism, which he initially believed to be quite different from the forms of childhood “psychosis” then recognized. In the subsequent six decades autism has been the focus of considerable interest from clinicians and researchers alike so that, for example, a large body of work both on research and intervention is now available (Volkmar et al., 2005).

Autism has been the focus of a very substantial body of work. While major advances have been made in both treatment (NRC, 2001) and research (Volkmar et al., 2005) precise pathophysiological models have yet to be specified. In an attempt to specify such models essentially all the theories of psychology and neurobiology have been utilized. While specification of such mechanisms remains an important, if as yet unrealized, goal considerable accomplishments have been made.

Introduction

Autism and other pervasive developmental disorders (PDDs) are a phenomenologically related set of neuropsychiatric disorders. These conditions are characterized by patterns of both delay and deviance in multiple areas of development; typically their onset is in the first months of life (APA, 1994; Volkmar & Klin, 2005). Although often associated with some degree of mental retardation, the pattern of developmental and behavioral features differs from that seen in children with mental retardation not associated with PDD in that certain sectors of development, such as social interaction and communication, are most severely affected whereas other areas, such as nonverbal cognitive abilities, may be within normal limits. While the validity of autism has been relatively well established, issues of syndrome boundaries remain the topic of some debate (Bailey et al., 1996). In this chapter, the development of autism as a diagnostic concept, current definitions of the condition and of related diagnostic concepts, and their differentiation from other disorders will be reviewed.

Development of diagnostic concepts

Over the past 150 years, a major point of controversy has been the continuity, or discontinuity, of the severe psychiatric disorders of childhood with the adult psychoses. For example, the great British psychiatrist Maudsley suggested that children, like adults, could exhibit “insanity” (1867).