What is the nature of the autism 'spectrum'?

Abstract

‘Autism spectrum’ as a term was introduced by Lorna Wing to describe the wide range of presentations from the original concept of autism proposed by Leo Kanner to the milder type of autism with relatively high communication skills and normal intelligence, which was named Asperger's syndrome after the case report of Hans Asperger. Most clinicians believed that the difference between autism and Asperger's disorder depends on the degree of severity, and the concept of autism spectrum has been widely accepted. In the DSM-5, autistic disorder, Asperger's disorder and pervasive developmental disorder not otherwise specified are grouped into one category named autism spectrum disorder (ASD). ASD diagnosis is based on: (i) persistent deficits in social communication and social interaction across multiple contexts; and (ii) restricted, repetitive patterns of behavior, interests, or activities. Although autism (previously called ‘childhood schizophrenia’) was named after Eugen Bleuler's concept of ‘autism’ in patients with schizophrenia, empirical evidences revealed that autism spectrum disorder should be differentiated from schizophrenia. Recent studies shed light on the association between ASD and schizophrenia. A follow-up study reported that a prior diagnosis of ASD or of other neurodevelopmental disorders was given among two-thirds of childhood-onset schizophrenia patients.1 Neuropsychological and psychophysiological testing suggests that social interactions, communication, emotion processing, sensorimotor gating and executive function are impaired in both disorders. In addition, genetic studies revealed that copy number variations, such as 15q13.3del, 16p11.2del and 22q11.2del, overlap between the two disorders.2 These findings suggest a continuity between ASD and schizophrenia. On the other hand, the family members of autistic probands have an increased likelihood of exhibiting autistic symptoms with a wide range of severity, often below the threshold for a diagnosis of an ASD (broader autism phenotype).3 This fact not only suggests the hereditary nature of autistic traits, but also questions whether or not ASD is a discrete disorder. Furthermore, many studies have reported that the prevalence of ASD is dramatically increasing. It is believed that the increase is not an ‘actual’ increase, but likely contributed to by extrinsic factors, such as increased awareness and diagnostics.4 This also suggests the difficulty in determining the diagnostic threshold for ASD. It is possible that autistic traits are distributed across the population and constitute the spectrum from typically developing to classical autism. To reveal the nature of the autism spectrum, it is no longer sufficient to compare the typically developing controls and patients with ASD. The relations among genetic and environmental factors, phenotype (autistic traits or endophenotypes), treatment response, brain structure and brain activity should be examined in comparatively large samples. The present volume features original studies on neurodevelopmental disorders. Egawa et al. (131–135) have examined the associations between OXTR (oxytocin receptor) variations and susceptibility for ASD. Hasegawa et al. (136–144) reveal the association between autistic traits in mothers and social responsiveness in children with ASD. Hosokawa et al. (145–152) demonstrate the relations among autistic traits, impairments in fearful facial recognition and fewer hemodynamic changes in recognizing negative facial expressions. A magnetoencephalography study by Hiraishi et al. (153–160) reveals an unusual pattern of brain lateralization in ASD. Ota et al. (161–170) report improvement in prefrontal hemodynamic changes after atomoxetine administration in children with attention-deficit/hyperactivity disorder. Finally, Hirota et al. (171–177) report the present condition of clinical practice and education in child and adolescent psychiatry in the Far East. We are convinced that these original articles will contribute to the understanding of neurodevelopmental disorders, and that readers will be inspired by the new findings.