Autism has been researched for more than 60 years, but until recently little focus has been placed upon the sleep problems often associated with it. Even within the sleep community, few have studied the relationship of sleep and autism. Much greater attention in our field has to be focused on autism because of the impact of sleep problems on the individual and others who typically have reported the most significant impacts, such as caregivers and the household.¹ With a greater focus on autism and the sleep problems associated with the disorder, sleep medicine professionals can more confidently and appropriately address the sleep-related issues linked to the population with autism.

CLINICAL DEFINITION OF AUTISM

In 1943, Leo Kanner, MD,² first used the term "autism" to describe a complex set of characteristics he noticed in 11 male children—impaired communication and social interaction, as well as stereotypical behavior. While Kanner and Asperger³ independently provided the original clinical background accounts of autism and what has become known as Asperger syndrome (AS), prior to these dates those with autism were likely labeled as "wild" or "feral."⁴ Recorded contemporary history of autism began at least in the mid-18th century with one of the earliest putative cases of autism: Hugh Blair of Borgue.⁵,⁶

The characteristic triad of impairments identified in early clinical research on autism has essentially endured over time.⁷ The essential features of autism described in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) still encompass Kanner's three characteristics, with an early childhood onset.⁸ However, diagnosticians have now recognized that a wide spectrum of phenotypes exist, which has given rise to the term autism spectrum disorders (ASDs), which includes autistic disorder, AS (or Asperger's disorder), and pervasive developmental disorder not otherwise specified (PDDNOS). A condensed representation of the DSM-IV-TR diagnostic criteria for autistic disorder is provided in Table 1. With the growing awareness, diagnosis of ASDs, prevalence (0.6% prevalence rate⁹), and the number of children with ASDs and sleep problems, knowledge of ASDs and sleep has become a significant issue that sleep centers will have to continue to address.

SLEEP PROBLEMS ASSOCIATED WITH AUTISM

Reports of high rates of sleep problems in young children with autism have a long history.¹⁰,¹¹ Sleep difficulties have appeared to be more common in younger children, but can be persistent through childhood and adolescence for many children. Children with autism have difficulty settling with long sleep latency, wake for long periods, and have shortened night's sleep and early morning waking.^12,13 Compared with typically developing children and children with other developmental disorders, children with autism have been distinguished by a higher rate of settling difficulties and co-sleeping.¹⁴ Research has continued to confirm the high rate of sleep problems in autism as well as AS and PDDNOS,^15-21 with additional problems reported including enuresis, parasomnias, high variability or delay in sleep onset and wake times, and daytime sleepiness.

Studies using actigraphy have also supported the presence of sleep problems in both autism and ASD.^15,22-24 The study by Wiggs and Stores probably has been the most comprehensive.²⁴ In this study, the sleep patterns of children with an ASD appeared compromised regardless of whether they had a parent-reported sleep problem. Long sleep latencies, delayed or advanced sleep onset and waking, night waking, low sleep efficiency, and abnormal activity pattern during the night were reported, thus generally confirming diary and questionnaire reports.

Sleep abnormalities have also been confirmed in a number of recent polysomnography studies.^25-30 Longer sleep latency and frequent night waking, lower sleep efficiency, alterations to non-REM sleep stages, lower sleep spindle density, a variety of REM sleep abnormalities, REM sleep behavior disorder, periodic limb movements in sleep, obstructive sleep apnea, and reduced sleep in the first two thirds of the night have been reported. However, these studies have had low participant numbers (<20), variously have included adults and children, and have covered a wide range of intellectual functioning.

Thus, actigraphy and polysomnography studies have indicated that a range of sleep difficulties have been commonly reported in children with ASDs that likely have had some biological foundation. Additionally, medical conditions, medication,¹⁸ and anxiety^12,16,24 have been associated with sleep difficulties. This initial connection to anxiety and additional evidence of a behavioral component and amenability of sleep problems such as settling and night waking to behavioral interventions have led researchers to explore the daytime correlates with sleep problems in this population.

IMPACT OF SLEEP PROBLEMS IN AUTISM

Within other populations, the sleep problems reported above have been suggested to cause daytime problems, such as decreased learning rates and decreased cognitive and creative performance^31-34; altered emotional states^32,34,35; impaired flexibility to change^31,33; increased general behavior problems^34,36; noncompliance³⁷; inattention to task³⁴; irritability³⁵; depression³⁵; hyperactivity³⁶; aggression³⁶; and self-injurious behavior.³⁸ No research has indicated that in the population of people with an ASD, sleep problems and disorders have caused problems with daytime behavior. However, evidence has suggested a relationship.

Initial research has designated a variety of daytime behaviors related to sleep problems for people with an ASD. Some researchers have suggested that the intensity of developmental disturbances³⁹ and general autism symptoms⁴⁰ is increased in relation to sleeping problems. Further research delineating the relationships among some of the key diagnostic factors in ASDs (eg, communication difficulties, stereotypic behavior, difficulties breaking routines, and social problems) has indicated that intensified symptoms in these areas are related to disturbed sleep.^18,39-41 Other more general daytime behavior problems have been reported as related to sleep problems for people with an ASD, such as overactivity,¹³ psychopathology,¹² and disruptive behavior.¹²

Autism and sleep disorder research are relatively new areas of investigation. While the relationships between autism and sleep problems have not been thoroughly explored, associations have been identified. These foundational research findings can be advantageous in improving quality of life in these patients with autism.

David B. Harrell, PhD, FRIPH, entered molecular biology more than 15 years ago and began focusing upon sleep in 2001. One of his research focuses since then has been sleep in children with and without autism spectrum disorders. He is innovation research director at Pro-Tech in Mukilteo, Wash. Kimberly A. Schreck, PhD, BCBA, is an associate professor in psychology and coordinator of the Applied Behavior Analysis Masters Program at Penn State University—Harrisburg. She has been researching and treating sleep problems for young children with and without autism spectrum disorders for approximately 12 years. Amanda Richdale, PhD, MAPS, is a psychologist and university lecturer who has worked in the field of autism for 20 years. One of her research focuses has been sleep problems in autism and in other developmental disabilities. She is associate professor of developmental psychology at the School of Health Sciences, RMIT University, Melbourne, Australia.

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