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Autism Spectrum Disorders in Later Life

Summary and Keywords

Autism spectrum disorder (ASD), or autism, is a neurodevelopmental disorder that is typically recognized and diagnosed in childhood. There is no established biological marker for autism; rather, the diagnosis is made based on observation of behavioral traits, including (a) persistent deficits in social interaction and communication, and (b) restricted, repetitive patterns of behavior, interests, or activities. Because autism is a spectrum disorder, autistic individuals are a highly heterogeneous group and differ widely in the presentation and severity of their symptoms. The established prevalence of ASD is approximately 1% of the population.

Information about autism in adulthood is limited; most of the literature examines childhood and adolescence. While the term “later life” has traditionally been associated with those over the age of 65, a dire lack of understanding exists for those on the autism spectrum beyond early adulthood.

Individuals remain on the spectrum into later life, though some mild improvements in symptoms are observed over time. Autistic adults experience high levels of physical and mental health comorbidities. Rates of participation in employment and education are also lower than that of the general population. Quality of life is reportedly poorer for autistic adults than for nonautistic peers, though this is not affected by age. More robust studies of the health, well-being, and needs of autistic adults are needed, especially qualitative investigations of adulthood and aging and longitudinal studies of development over the lifespan.

Keywords: autism spectrum disorder, developmental disability, intellectual disability, aging, adults with disability, neurodiversity, ASD, autism

Background and History of ASD

Autism spectrum disorder (ASD), or autism, is a neurodevelopmental disorder that is believed to originate in the brain and typically manifests before a child reaches school age. In DSM-V, the fifth edition of the Diagnostic and Statistical Manual for Mental Disorders (American Psychiatric Association, 2013), a clinical representation of autism includes persistent deficits in social communication and social interaction across multiple contexts, and restricted, repetitive patterns of behavior, interests, or activities. These behavioral symptoms must be present during the early developmental period, cause clinically significant impairment to important areas of functioning, and not be better explained by intellectual disability or global developmental delay. Another key feature of autism listed under the DSM-V criteria is hyper- or hyporeactivity to sensory input or unusual interests in sensory aspects of the environment (American Psychiatric Association, 2013). Such experiences span the sensory domains of visual, audio, tactile, olfactory, and vestibular (Robertson & Simmons, 2015) and have been reported to occur in the vast majority of autistic individuals (Crane, Goddard, & Pring, 2009). Such experiences can be problematic or helpful (or both) for autistic adults, the implications of which may affect participation in employment and leisure activities, social functioning, and other daily activities. Overall, determination of the severity of ASD is based on the level of support the individual requires.

Intellectual disability and epilepsy commonly occur in autistic individuals, though reported rates of comorbidity tend to vary widely for both conditions. Studies investigating the presence of intellectual disability in autistic individuals have reported figures between 25% and 75% (Bourke, De Klerk, Smith, & Leonard, 2016; Matson & Shoemaker, 2009), while comorbidity for epilepsy and autism has been reported to be between 2% and 26% (Amiet et al., 2013; Viscidi et al., 2013). More recent studies tend to report higher rates, and this may be attributable to the widening of diagnostic criteria for ASD over time. Studies have reliably documented a greater prevalence of ASD for males than females; a 4:1 ratio is frequently cited in the literature (Halladay et al., 2015). Underdiagnosis of females may be a factor that contributes to this gender difference. Females with higher IQs or with less severe autism may have less likelihood of being diagnosed with ASD than their male counterparts (Lai & Baron-Cohen, 2015; Van Wijngaarden-Cremers et al., 2014). Similarly, females may be better able to hide or mask their autism symptoms than males (Gould & Ashton-Smith, 2011). Autistic individuals thus represent a highly heterogeneous population, with varying symptom severity, levels of functioning, and subsequent support needs.

The origins of ASD as a diagnosis can be traced back to the work of the Austrian pediatric psychiatrist Leo Kanner, who observed and described “early infantile autism” in his 1943 paper “Autistic Disturbances of Affective Contact” (Kanner, 1943). In it, Kanner described a sample of children who he believed had been born into the world lacking social predispositions and who were highly resistant to change. Since then, ASD has undergone a range of conceptual revisions. The first recognition of the condition appeared in the third edition of the Diagnostic and Statistical Manual for Mental Disorders, where it was called “infantile autism” and identified as a pervasive developmental disorder (American Psychiatric Association, 1980). Soon after, during the revision of the third edition, autism was newly termed “autistic disorder” to reflect its developmental nature. The fifth and most recent version of the DSM reconceptualized ASD as a dimensional condition, merging autistic disorder, Asperger’s disorder, and pervasive developmental disorder not otherwise specified under the umbrella term autism spectrum disorder.

The estimated prevalence of autism in Western countries has been close to 1% (Baron-Cohen et al., 2009; Elsabbagh et al., 2012), with some estimates as high as 2.6% (Kim et al., 2011). This is a notable increase from figures published in the 1990s and earlier that suggested a prevalence of between four and 12 per 1000 persons (Baird et al., 2006). Studies have noted a clear increase in the prevalence of ASD in children from the late 1990s to 2010s and propose reasons for this trend (Atladottir et al., 2015; Elsabbagh et al., 2012). Aside from the possibility of a true increase in prevalence of ASD, the authors of these studies have attributed the increase to broadened diagnostic criteria, increased public and clinical awareness of ASD, and increased availability of diagnostic services. Data on the specific prevalence of ASD in adulthood is scarce. The best estimate available at present is from an British study reporting the prevalence of autism in adults to be approximately 1% (Brugha et al., 2016).

Continuation Into Later Life

Autism is a lifelong condition (Levy & Perry, 2011). Unfortunately, there is a dire lack of both robust research and available supports for autistic individuals beyond the post-school transition period of 18 to 25 years of age. The relatively short history of autism as a diagnosis has meant that the first cohorts of children diagnosed with ASD have only recently begun to enter middle age and older adulthood. As such, investigations of the presentation, correlates and trajectory of autism in adulthood remain scarce in comparison to those involving children and adolescents. A majority of research has focused on early years, such as the genetic underpinnings of ASD and early intervention. A small but growing body of research is available on autism in adolescence and young adulthood. The general lack of research examining autistic adults at all stages of adulthood has caught the attention of researchers, families and national organizations alike (Wright, Brooks, D’Astous, & Grandin, 2013). This paucity of evidence is particularly prominent for adults beyond middle-age (45 years and over). A 2016 systematic review found only 12 published articles specifically examining these older adults on the autism spectrum (Patra, 2016). The oldest article was published in 2013, indicating the recency of interest.

Autistic children experience significant impairments in their daily living skills (Perry, Flanagan, Geier, & Freeman, 2009). Although further skills development occurs with age, even into their 30s, the improvements are conservative, and the skills of autistic adults remain lower than for nonautistic adults in adulthood (Bal, Kim, Cheong, & Lord, 2015; Smith, Maenner, & Seltzer, 2012). Moreover, the gap between developmental skills, such as age-appropriate social and communication abilities, and daily living skills for those on the spectrum becomes more pronounced with increasing age (Klin et al., 2007).

A range of studies have investigated the relationship between the ASD symptom profile and age. In general, according to both clinical observation and family reports, autism symptoms undergo a general decrease over time as the child gets older (Billstedt, Carina, Gillberg, & Gillberg, 2007; Levy & Perry, 2011; McGovern & Sigman, 2005). However, these decreases are seldom large enough for the individual to be deemed no longer autistic. Some studies do report that a minority of autistic children do not meet the diagnostic criteria for autism in later years (Cederlund, Hagberg, Billstedt, Gillberg, & Gillberg, 2008; Helt et al., 2008), though such results remain controversial, and some argue that these findings are anomalous or are the result of an initial misdiagnosis. Overall, studies converge on the idea that a majority of autistic children retain their autism diagnosis throughout adulthood.

Some variation is seen in the patterns of symptom improvement over time, as difficulties in social interaction, communication, and adaptive behaviors tending to improve, whereas stereotyped interests and repetitive behaviors are more stable over time (Howlin, Goode, Hutton, & Rutter, 2004). Studies have noted such factors as absence of intellectual disability, higher family income, earlier diagnosis and treatment, and less-severe symptoms at diagnosis as common predictors of achieving a “better outcome” or a decline in autism symptoms in later life (Helt et al., 2008; Taylor & Seltzer, 2010); whereas those with more severe intellectual impairment and those with comorbid psychiatric problems retain their symptoms long term (Matson & Shoemaker, 2009). Yet despite these symptomatic improvements, autistic individuals continue to experience symptoms and associated impairments into adulthood.

Terminology, Neurodiversity, and Sociopolitics

It is important for researchers and practitioners to approach any disability with an understanding of the sociopolitical discourse that surrounds it. For autism in particular, there is ongoing discussion related to terminology and the concept of “neurodiversity.” The attitudes and perspectives involved in these discussions can be understood within the broader context of the disability rights movement of recent decades.

The “language” that develops in association with any new diagnosis has the potential to reflect and influence people’s attitudes toward the condition. Person-first language (e.g., “person with autism”) has been the preferred approach for addressing people with specific disabilities; however, opinions on this issue in the ASD community often deviate from this view. Person-first language arose in the context of the disability rights movement (Blaska, 1993), and it has been widely embraced by health professionals (Kenny et al., 2015). However, some members of the autism community have expressed a preference for disability-first language (e.g., autistic person). This view is especially endorsed by those who accept their diagnosis as a central and positive feature of their identity, and it aligns with the recent notion of neurodiversity (Kapp, Gillespie-Lynch, Sherman, & Hutman, 2012) in which autism is seen as one type of a diverse range of human minds. Meanwhile, some evidence from the United Kingdom has suggested that the term “on the autism spectrum” may be a mutually agreeable for the adults, healthcare professionals, and members of the general population (Kenny et al., 2015). Debate in this area is likely to persist, because preferences for terminology continue to differ not only between different groups but within them too.

There has been much discussion in print and in online forums regarding the term neurodiversity. At its core, neurodiversity posits that there is diversity in human neurobiology, and that autism is but one specific type. Following on from this is the belief that all types of neurobiology, including autism, are valuable. The neurodiversity movement advocates reconceptualizing autism as a difference, rather than as a deficit in need of “fixing” (Kapp et al., 2012). A change in language that is based on a change in attitudes toward autistic individuals may bring about important changes in the priorities and attitudes that inform research and policy development.

Meanwhile, in the aging scholarship, theories of aging are moving toward more positive conceptualizations of later life. This move parallels those in the neurodiversity movement. Instead of assuming that those who are older (or those with disability) are necessarily disadvantaged, these developments encourage a shift in focus away from limitations to embrace the unique opportunities and strengths of the person.

Health

Physical Health and Daily Functioning

Health concerns are well-documented in children and adolescents on the spectrum. In contrast, the health and functional statuses of adults are much less understood. Although the literature is thin, population-based studies consistently describe higher rates of comorbid conditions for autistic adults in comparison to the nonautistic population (for a review, see Cashin, Buckley, Trollor, & Lennox, 2016). A review of retrospective health records of 1,507 autistic adults over 18 years of age found significantly higher rates of immune and gastrointestinal disorders, hyperlipidemia, hypertension, cerebrovascular diseases, and seizures in comparison to the sample of 15,070 nonautistic adults in the United States (Croen et al., 2015). Further, significant medical comorbidity burdens have been found; one study reported a median number of 11 comorbid medical conditions in their population-based cohort of autistic adults, regardless of intellectual disability (Jones et al., 2015). There is a general lack of understanding regarding the development of age-related conditions in adults on the spectrum. A study by Starkstein and colleagues reported that 20% of their sample of 37 autistic adults over the age of 39 from the United States and Australia displayed Parkinsonian symptoms (Starkstein, Gellar, Parlier, Payne, & Piven, 2015). Increased prevalence of diabetes mellitus (type 1) has also been identified in autistic adults (Kohane et al., 2012).

Research on the cognitive functioning of autistic adults is still in its youth, and only a few studies to date have examined performance and age-related changes in this population, with mixed results. Several different trajectories of cognitive functioning have been documented for autistic adults. First, there is some evidence that age-related declines in verbal memory and theory of mind (Geurts & Vissers, 2012; Lever & Geurts, 2016a) in ASD adults parallel those observed in the general population. However, being autistic may also compound “natural” age-related declines in cognitive processes, such as learning, processing speed, and cognitive flexibility (Geurts & Vissers, 2012; Powell, Klinger, & Klinger, 2017). Finally, some studies have suggested that in some aspects of cognitive functioning, autism may be a protective factor, especially for processes such as visual memory (Lever & Geurts, 2016b). Related to this last hypothesis, it has been suggested that autistic adults may have a “hyperplastic brain” (Oberman & Pascual-Leone, 2014), which may afford relative protection from dementia and Alzheimer’s disease (Oberman & Pascual-Leone, 2014).

Excess and premature mortality are also consistently found for those on the spectrum. Large studies in Sweden, the United States, and Denmark have found elevated mortality rates for autistic populations, approximately twice over those of the general population (Hirvikoski et al., 2015; Schendel et al., 2016; Shavelle, Strauss, & Pickett, 2001). Furthermore, compared to the general population, life expectancy is reduced by 9 years for those with ASD without intellectual disability and by 30 years for those with ASD and intellectual disability (Hirvikoski et al., 2015). A prominent cause of early death in autistic individuals, particularly those without intellectual disability, is suicide (Hirvikoski et al., 2015). Outcomes also appear heavily impacted by the complex medical comorbidities present in those on the spectrum (Schendel et al., 2016).

Some health domains appear to be unevenly affected. Oral health has been found to be comparable in those with and without ASD (Blomqvist, Bejerot, & Dahllof, 2015). Lower rates of sexually transmitted diseases, smoking, and alcohol and drug abuse have been observed (Fortuna et al., 2015). However, sleep quality has been found to be poorer for adults on the autism spectrum (Richdale & Schreck, 2009), and the incidence of obesity higher (Croen et al., 2015).

Mental Health

High rates of psychiatric comorbidity are found for individuals on the spectrum. Lifetime rates for psychiatric disorders such as depression, anxiety, psychosis, and obsessive-compulsive disorder (OCD), are high for those with ASD, with reported rates of 69% to 79% (Buck et al., 2014; Lever & Geurts, 2016b). A presence of psychiatric disorder appears to parallel ASD severity. Those with higher self-reported and observed autism symptoms also display higher rates of psychiatric symptoms and lifetime psychiatric disorders (García-Villamisar & Rojahn, 2015; Sterling, Dawson, Estes, & Greenson, 2008).

A Dutch investigation concluded that psychiatric conditions, especially social phobia and depression, tend to be less prevalent in older autistic adults than in middle-aged or younger ones (Lever & Geurts, 2016b); this is similar to the age-related decline in mental disorders in the general population. Nevertheless, these conditions are present and persist throughout adulthood. Of the range of psychiatric comorbidities experienced by autistic individuals, social anxiety and depression stand out in literature (Croen et al., 2015; Lever & Geurts, 2016b).

There are significant challenges in the proper identification and management of psychiatric disorders in autistic adults. For autistic adults who display differences in social interactions, communication, and behaviors, psychiatric disorders may manifest in atypical ways (Ghaziuddin & Zafar, 2008). This is particularly likely for those with lower IQ or comorbid intellectual disability, or both, and it presents challenges for the proper identification of these disorders. There may also be an overlap between the symptoms present in certain mental health conditions and the ASD symptom profile, resulting in diagnostic overshadowing. Poor identification of these disorders has related implications for their management. Inappropriate and overprescription of psychotropic drugs has been found for those on the spectrum, and there have been some reports of antipsychotic and antidepressant drugs being prescribed to those with ASD in the absence of an appropriate diagnosis (Esbensen, Greenberg, Seltzer, & Aman, 2009; Public Health England, 2015). In addition to better understanding of the manifestation of psychiatric disorders in autistic adults, there is a need for primary healthcare providers to be upskilled in the identification of mental health concerns in autistic adults (Zerbo, Massolo, Qian, & Croen, 2015) to ensure their effective and appropriate management.

Overall, there remains a lack of evidence, especially from population-based studies examining the presence of physical and mental health comorbidities in autistic adults beyond middle age. Longitudinal studies tracking the trajectory of physical and mental health as autistic adults age are also lacking, and relatedly, causal relationships between determinants and health outcomes remain unclear. In particular, considering the studies suggesting the high rates of comorbidities present in autistic populations, a focus on how such preexisting conditions may interact with age is needed.

Healthcare

Numerous studies have reported that autistic adults, despite having elevated medical comorbidities and considerable subsequent health burdens, experience significant barriers to healthcare and associated lower satisfaction with healthcare, lower self-efficacy in navigating healthcare systems, and greater unmet needs in this domain (Nicolaidis et al., 2013). Healthcare professionals report a lack of confidence about providing medical care to patients on the spectrum, and challenges found throughout the systems, practices, and training levels of care provision (Warfield, Crossman, Delahaye, Der Weerd, & Kuhlthau, 2015). ASD symptomatology is likely to create difficulties in terms of interaction with healthcare systems. In general, the barriers to healthcare that autistic adults experience are similar to those with other disabilities, such as mobility or learning impairment, though autistic adults experience them at a higher rate (Nicolaidis et al., 2013; Raymaker et al., 2016). In addition, some barriers are specific to autism symptomatology, such as sensory sensitivity and difficulty coping with change (Raymaker et al., 2016). Not all autistic adults report dissatisfaction with their healthcare, however. Autistic individuals with no concurrent intellectual disability have been reported to show satisfaction with services such as occupational therapy and physiotherapy (Vogan, Lake, Tint, Weiss, & Lunsky, 2017). It was reported that dissatisfaction with healthcare may be related to having additional comorbid mental and physical health problems (Vogan et al., 2017). Because the need for healthcare increases with age, instruments and training to better equip those involved in autistic adults’ interactions with healthcare are needed.

There have been no specific investigations of geriatric healthcare or care management for the elderly with ASD. Older populations in general tend to experience higher prevalence of chronic diseases, functional disabilities, and mental illnesses (Boutayeb & Boutayeb, 2005), compounded in autistic individuals by the already elevated levels of medical comorbidities (Croen et al., 2015), making it likely that a more complex care will be required for autistic adults as they age. An investigation of the lifetime distribution of the costs of autism to society in the United States reported that the second largest component of these costs were those required for care of autistic adults (Ganz, 2007). Specific understandings of the differing healthcare requirements for autistic adults as they get older are necessary. The development and delivery of appropriate palliative services for autistic adults is important and will be increasingly so as more autistic adults reach older age. There is one available written guide, published by the British Institute of Learning Disabilities in the United Kingdom, containing information for those who provide care to individuals on the spectrum during the final stages of their lives (Ferguson & Laurie, 2015).

Education and Employment

Despite those on the spectrum having the ability and desire to work, the labor force participation of autistic adults has been generally much lower than for the general population (Hendricks, 2010). According to a systematic review of social participation for adults on the spectrum, seven studies reported that between 6.3% and 37.1% of autistic adults were employed full-time at the time of the study, whereas 25% to 75% were unemployed (Tobin, Drager, & Richardson, 2014). Sheltered workshops or day activity centers are common daytime activities for this population in general (Taylor & Seltzer, 2011). A review of literature found the only consistently significant predictor of work participation for autistic individuals was IQ, and that higher IQ predicted better employment outcomes (Holwerda, Van Der Klink, Groothoff, & Brouwer, 2012). Importantly, high levels of underemployment (Tobin et al., 2014) and employment instability (Eaves & Ho, 2008) are found for autistic populations. A longitudinal study tracing employment and postsecondary education activities of adults on the spectrum over 12 years found that only a quarter of the sample was consistently engaged in these activities (Taylor, Henninger, & Mailick, 2015).

Employment is an important contributor to well-being in adulthood. Work participation is important at the individual level, for both providing a means of living and contributing to identity formation (Krieger, Kinébanian, Prodinger, & Heigl, 2012), and at the societal level, for alleviating the demographic pressures of aging. The low rates of employment are particularly concerning when considering the negative effects of employment precariousness on the mental health of adults (Julià, Vanroelen, Bosmans, Van Aerden, & Benach, 2017). For the general population, numerous studies have indicated the physical and mental health benefits of employment (Modini et al., 2016) and re-employment (Schuring, Mackenbach, Voorham, & Burdorf, 2011).

A number of challenges in gaining and maintaining employment have been identified to occur throughout the employment process, from application to adaptation and integration (Muller, Schuler, Burton, & Yates, 2003). These challenges are often caused or exacerbated by the social interaction and communication differences present in autistic adults. Difficulties in social interactions with coworkers and supervisors are commonly reported and, in some instances, lead to termination (Hendricks, 2010). Other challenges for successful employment include differences in cognitive functioning, which in autistic adults manifest as difficulties with problem-solving or organization, even in those with normal or high intelligence (Barnhill, 2007), and behavioral differences, such as repetitive behaviors or tantrums. These challenges likely form a vicious cycle of preceding and resultant stress or anxiety in the workplace, which is found to be high for autistic individuals (Hurlbutt & Chalmers, 2004). Completion of postsecondary education has been shown to improve employment outcomes and the subsequent quality of life for autistic individuals (Hart, Grigal, & Weir, 2010). Longitudinal data following 4,810 young adults with disabilities from the United States found that those with ASD were less likely to go on to postsecondary education in comparison to those with learning disabilities and other impairments (Newman et al., 2011). In particular, young autistic adults from lower-income households and with greater functional impairments are less likely to be involved in postsecondary education after high school (Shattuck et al., 2012). Significant challenges are reported for autistic individuals, both in the process of making the postsecondary transition and in subsequent education settings. These include a lack of appropriate and adequate transition planning (Shattuck et al., 2012), facing new people and situations and forming and maintaining new social relationships, and managing time and work tasks (Van Hees, Moyson, & Roeyers, 2014). Improving this outcome will depend on interventions targeted at both the individual level, such as improving social and living skills, and the educational and faculty level, such as improving the accommodations offered by postsecondary institutions (Zeedyk, Tipton, & Blacher, 2016).

There is no available information on the continued education, employment, retirement and postretirement circumstances of older adults on the autism spectrum. Being employed has been found to be important to physical and mental health in nonautistic older adults (Modini et al., 2016; Schuring et al., 2011), and unemployment has been found to be related to more illness (Bartley, Sacker, & Clarke, 2004). Sustained productive and intellectually demanding work has been shown to be positively associated with cognitive performance in later life (Potter, Helms, & Plassman, 2008), whereas retirement has been negatively associated with cognition (Bonsang, Adam, & Perelman, 2012). These findings have yet to be replicated in autistic adults. Because of the difficulties they face in gaining and maintaining employment, autistic adults may be forced into premature retirement. In a qualitative investigation of aging ideals, autistic adults and carers also expressed the desire to continue engagement in any form of meaningful and rewarding day activities, and they considered stable employment to be precious (Hwang, Foley, & Trollor, 2017). It is important to understand retirement circumstances and associated personal and environmental factors for autistic adults in order to ensure optimal levels of activity and health are maintained in later life.

Social and Relational Issues

Social interaction and communication are inherently different for those on the autism spectrum compared to nonautistic individuals, yet both are key and influential in building and maintaining relationships with others. Because socialization and communication are core aspects of ASD, these issues have been well-examined in children and adolescents on the spectrum, but these issues are far less explored in adulthood. Qualitative investigations have found social and relational issues to have a profound influence on life and well-being of autistic adults (Griffith, Totsika, Nash, & Hastings, 2012; Hwang et al., 2017; Müller, Schuler, & Yates, 2008). Interviews with adults on the spectrum reveal that the social interactions required in daily life are difficult for some autistic individuals and present particular challenges in the workplace (Griffith et al., 2012). Autistic adults reported that a general lack of knowledge about ASD was a key driver of such difficulties (Griffith et al., 2012). Quantitatively, differences and difficulties in the quality and quantity of peer relationships have been repeatedly observed for this population. An investigation of peer relationships reported that of the sample of 235 autistic adolescents and adults who were living at home, almost half had no similar-aged peers with whom they had a reciprocal relationship, whether prearranged or not (Orsmond, Krauss, & Seltzer, 2004). Social isolation and being bullied are unfortunate but common experiences for those on the spectrum (Weiss, Cappadocia, Tint, & Pepler, 2015). But again, the evidence for adults is limited because most studies focus on primary and secondary educational settings.

Information about the social networks and relationships of older autistic adults is particularly lacking. Evidence from the general population suggests that social isolation and loneliness increase with age (Pinto & Neri, 2017). At the same time, the benefits of social connectedness and support on cognitive performance (Elovainio et al., 2018), physical health, and mental health have been established in the general population, as have the negative consequences of a lack of social contact (Holt-Lunstad, Smith, & Layton, 2010). Although similar findings are lacking in autistic populations, it is likely that the lack of social support and connectedness found for autistic adults continues and worsens in later life, and that it is further amplified by retirement from productive activities. A qualitative investigation found that bullying, social isolation, and ostracism impacted well-being for autistic adults as they aged (Hwang et al., 2017). Given the significant and long-lasting impacts, more investigations of social connectedness, support, isolation, and bullying for middle-aged and older adults are needed.

A particularly poorly understood area of life for autistic adults is that of sexual and romantic relationships. A small but increasing number of studies have focused on the romantic and sexual interest, knowledge, experience, and behavior of autistic adults. In contrast to past beliefs that autistic adults are unable or unwilling to form long-term, romantic relationships, it has been found that adults on the autism spectrum desire and engage in a range of romantic and sexual relationships (Byers, Nichols, Voyer, & Reilly, 2012; Hellemans, Roeyers, Leplae, Dewaele, & Deboutte, 2010). Although sexual and romantic experiences are not uncommon in autistic adults, their experiences and knowledge are markedly less than those of the general population (Mehzabin & Stokes, 2011). There have also been reports that autistic adolescents and adults engage in inappropriate courting behaviors such as stalking, inappropriate touching, or inappropriate comments, significantly more than do nonautistic peers (Stokes, Newton, & Kaur, 2007). These findings may reflect the social interaction and communication differences present in autistic individuals and point to the need for specialized sex-education programs for this population, especially in adolescence. More broadly, rates of marriage and separation are unclear for autistic adults

Moving Forward

A General Knowledge Gap

Robust research is required to further explore the health, well-being, and experiences of autism in older adulthood. Not only is there a need to better understand health and well-being as it changes over time, but research is also needed on topics specific to aging. These include retirement, aged care, and end-of-life issues. Autistic individuals experience unique challenges in employment, employment transitions, and in receiving and accessing appropriate supports throughout adulthood. A lack of understanding of the unique needs and circumstances of autistic adults may precede insufficient or inappropriate care and support. To ensure the best quality of life for those on the spectrum in their later years, a greater understanding of these topics is therefore needed.

Most of the existing studies on autism have been published in Western countries, followed closely by non-Western developed countries. Although there has been some recent interest in the presentation and impact of ASD in different regions of the world, evidence in developing countries remains limited (Hahler & Elsabbagh, 2015). Global estimates of prevalence from 2012 reported rates of 1% to 2%, with epidemiological studies suggesting increasing prevalence over the past half-century (Elsabbagh et al., 2012). It is likely that the identification, sociocultural impact, and available supports for autism will differ widely between countries. It is therefore important for studies specific to the different regions of the world to be conducted and to serve as the foundation for improving outcomes for autistic individuals and their families worldwide. Although the study of autism in the developed world began with a heavy emphasis on childhood, in light of the recent recognition that autism is a lifelong condition, it is important that the emerging research in developing countries give due emphasis to middle-aged and older adults on the spectrum.

Researching Autism in Adulthood

Conducting research with adults on the autism spectrum presents specific challenges. Autistic adults have been referred to as a “hidden population” (Perkins & Berkman, 2012) because of the difficulties associated with identifying them. In addition to the relatively recent recognition of autism as a formal diagnosis, diagnostic practices for ASD in general have varied over time, and there are significant complexities involved in first diagnosing a developmental disorder in adulthood (Whitehouse, Evans, Eapen, Prior, & Wray, 2017). This means that it is likely that many adults on the spectrum have either not received a formal diagnosis or have been misdiagnosed with other conditions. Pathways for receiving a diagnosis in adulthood are heterogeneous (Geurts & Jansen, 2011), and the experience of being diagnosed has been found to vary (Lewis, 2016). As of 2018, there has been no research that explores the effects of delayed diagnosis for this population.

Importantly, difficulties in obtaining a formal diagnosis in adulthood presents challenges for research, especially when determining inclusion criteria for those without an official diagnosis. This may affect research validity, bias, and the representativeness of samples. For example, research has been conducted on the relatives of those with an autism diagnosis, who may display “milder,” subclinical levels of autism traits—they are described by the term “broad autism phenotype” (Wallace, Budgett, & Charlton, 2016). However, considering both the difficulties in diagnosing autism in adulthood and the broadening of diagnostic criteria for the autism spectrum, it is likely that at least some of these adults are autistic but have not received a formal diagnosis. For older adults without a formal diagnosis, barriers to identification and participation in research are likely compounded by the range of physical, functional, and social participation limitations they experience (Lewis, 2016). The practical inconvenience, physical difficulty, and stress of obtaining a formal diagnosis may outweigh the perceived benefits to the adult. Given the lack of opportunity, the complexity involved, and the likelihood that older adults have not obtained a formal diagnosis of autism, it may be preferable to include, rather than exclude, older adults who self-identify as autistic in research and to use appropriate screening or assessment tools to ensure the validity of the diagnosis.

A key challenge for future research is to develop appropriate and effective diagnostic tools and guidelines for diagnosing ASD in adulthood. Diagnosis of a developmental disorder in adulthood is difficult and further complicated by the fact that there is no established biological marker for autism. This means that diagnosis is based on a best-estimate, subjective judgment by a clinician using behavioral criteria. In most countries, there exists no golden standard or set of universally accepted guidelines for diagnosis (Whitehouse et al., 2017). Obtaining an accurate and timely diagnosis has direct impacts on the health and well-being of autistic individuals and their families because of the effect on health-service and education provision for the autistic individual. Qualitative work has suggested that obtaining a diagnosis is an influential experience on the well-being of individuals and their families, for reasons related to identity and to formal support needs (Hwang et al., 2017). Of all individuals on the spectrum, those with no comorbid intellectual disability are more likely to experience delayed diagnosis (Lehnhardt et al., 2013). Many existing tools refer to or rely on an informant’s judgment of the behavior of the individual during his or her early childhood. This is problematic for older adults, for whom an appropriate informant may not be available.

A related challenge is in developing measures that are autism friendly and, more specifically, autistic adult friendly. To collect meaningful and comparable information about the health and well-being of autistic adults, measures must be developed or adapted to ensure suitability and effectiveness for studying this population. Measures that have been developed for studying autistic individuals, especially diagnostic tools, have largely been targeted at children or childhood. It would be most useful to involve autistic individuals and those with the appropriate formal and informal experience with ASD in shaping these measures. The term inclusive research is often used in the field of intellectual disability to refer to the active participation in research of those with intellectual disability. It is useful concept to apply to the development of autism-friendly measures and has already been taken on as a core principle by research organizations such as the Academic Autism Spectrum Research Partnership in Research and Education (AASPIRE) in the United States and the Cooperative Research Centre for Living with Autism (Autism CRC) in Australia. Cooperation and collaboration between groups across countries would help to further streamline the process of tool development.

There a need not only for autism-friendly measures but also for autism-friendly research practices. As research and media interest in autism rises, it is likely that autistic individuals and their families have or will engage in a range of research studies. However, autistic adults exhibit a range of differences and difficulties in social interaction and communication and sensory sensitivities that may make research participation challenging. For older adults, limited participation in social activities may also mean they are out of the reach of distribution channels for materials that promote research participation. It is important to ensure that research practices are suitably developed with such differences in mind. A mixed-methods study found that two broad factors influence the research participation of autistic adults: participant values, such as whether they draw a sense of worth and inspiration from contributing to research, and convenience, such as the flexibility of the research location to accommodate different sensory preferences, and its accessibility (Haas et al., 2016). Some researchers actively report considerations for making research processes more autism friendly, such as the development of visual aids and using advisory networks consisting of members from the autism community to check the clarity and suitability of their materials and processes (Arthur-Kelly, Sigafoos, Green, Mathisen, & Arthur-Kelly, 2009; Hwang et al., 2017). This may be particularly relevant for qualitative investigations.

Qualitative and Longitudinal Studies

Besides the general paucity of research evidence exploring autism in adulthood, there is a lack of qualitative studies. There is a need to complement our growing quantitative understanding with the depth of information that qualitative investigations can offer. This is the philosophical assumption that underlies mixed-methods research (Creswell & Clark, 2011). Topics that would particularly benefit from qualitative investigations include explorations of the subjective, lived experiences of those on the spectrum and those intimately involved in their lives. These may include their experiences in healthcare systems, impact of getting the diagnosis, or challenges they have faced in education and employment. The programs of national and international autism conferences have increased the presence of those with “lived experience.” These findings may be taken together with existing or new quantitative data to complete our understanding of research questions and ultimately lead to the development of new tools, strategies, and initiatives that are more relevant, effective, and better received by end users.

Another rarity in autism research is longitudinal studies. There have been very few longitudinal investigations of autistic individuals that reach beyond young adulthood. The research questions that can be addressed by longitudinal studies are different and may offer clearer findings than cross-sectional designs. In addition to mapping age-related changes in health and autism symptoms over time, longitudinal studies may allow childhood predictors to be linked to important adult outcomes. These may include factors such as receipt of childhood intervention, functional status, and symptom severity, and their influence in middle and older adulthood, in areas such as social adjustment, employment, health, and mortality.

The Broadness of the Spectrum

The incorporation of the multiple diagnoses of previous DSM versions into one spectrum disorder has meant that a very heterogeneous group of individuals are assumed under one diagnostic label. The heterogeneity of outcomes and the complexity of disentangling cause, influence, and effect in the existing autism research may be in part influenced by the heterogeneity of the spectrum itself. It is thus useful to study smaller subgroups within autistic populations based on patterns and presentations of autistic traits, abilities, and support needs. This may improve researchers’ capacity to interpret findings, draw conclusions, and translate findings. One useful categorization would be to differentiate between those with and without comorbid intellectual disability. Other distinguishing variables may include the severity or presentation of autistic traits, age at diagnosis, presence of other comorbidities, and gender.

Conclusion

Autism spectrum disorder is a lifelong condition of growing prevalence. The vast majority of autism research has focused on children and adolescents, and research into adulthood and especially later life on the autism spectrum remains scarce. Available evidence suggests that autism symptoms persist into adulthood, and that autistic adults experience poorer health and well-being outcomes in comparison to adults from the general population. A more robust understanding of adulthood and aging on the autism spectrum is needed to better support and improve health, functioning, and engagement for this population. There are some challenges in identifying and researching autism in adulthood, and these must be carefully considered in future work. In addition to qualitative and longitudinal investigations, further understanding of aging-specific topics such as retirement and end-of-life care is needed.

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