All of the disorders described above can have their onset during childhood, adolescence, or adulthood. Some often begin early in life (lots of adolescents develop anxiety disorders or depression), and in fact half of all disorders begin by age 14, and three-quarters by age 24 (Kessler, Berglund, et al., 2005), which means if you are 24 years or older, you are almost out of the woods. However, other disorders tend not to begin until early adulthood, such as bipolar disorder and schizophrenia (we did say “almost”). Some disorders always, by definition, begin in childhood or adolescence, and if they do not, you are never going to have them. These include autism spectrum disorder, attention-deficit/hyperactivity disorder, conduct disorder, intellectual disability (formerly called mental retardation), learning disorders, communication disorders, and motor skill disorders, in addition to many others. The first three are among the most common and well known, so we will review them briefly here.

Marco is a 4-year-old only child. His parents have become worried because, although his mother stays home with him all day and tries to play with him and talk with him, he still has not spoken a single word and he shows little interest in trying. He spends much of his time playing with his toy trains, which seem to be the thing he enjoys most in life. He often sits for hours staring at spinning train wheels or pushing a single train back and forth, seeming completely in his own world, uninterested in playing with anyone else. Marco’s parents have become concerned about Marco’s apparent inability to speak, disinterest in others, and development of some peculiar mannerisms, such as flapping his arms repeatedly for no apparent reason.

Autism spectrum disorder (ASD) is a condition beginning in early childhood in which a person shows persistent communication deficits as well as restricted and repetitive patterns of behaviours, interests, or activities. In DSM–5, ASD now subsumes multiple disorders that were considered separate in DSM–IV: autistic disorder, Asperger’s disorder, childhood disintegrative disorder, and pervasive developmental disorder not otherwise specified (i.e., these disorders are no longer recognized in the DSM).

The true rate of ASD is difficult to pinpoint, especially given the recent change in diagnostic definition. Estimates from the 1960s indicated that autism was a rare diagnosis, occurring in 4 per 10 000 children. Estimates have been creeping up over time and now stand at approximately 10 to 20 per 10 000 children. If one considers the full range of disorders that now fall under the ASD umbrella in the DSM–5, the rate is 60 per 10 000 children (NEDSAC, 2012; Newschaffer et al., 2007). It is unclear whether this increased rate is due to increased awareness and recognition of ASD, better screening and diagnostic tools, or to some other factor. Boys have higher rates of ASD than girls by a ratio of about 4:1.

Early theories of autism described it as “childhood schizophrenia,” but it is now understood to be separate from schizophrenia, which is rarely diagnosed in children, emerging mainly in adolescence or young adulthood (Kessler & Wang, 2008). ASD is currently viewed as a heterogeneous set of traits that cluster together in some families (heritability estimates for ASD are as high as 90 percent), leaving some children with just a few mild ASD traits and others with a more severe form of the disorder (Geschwind, 2009). Interestingly, some people with ASD have unique strengths, such as remarkable abilities to perceive or remember details, or to master symbol systems such as mathematics or music (Happé & Vital, 2009).

One current model suggested that ASD can be understood as an impaired capacity for empathizing, knowing the mental states of others, combined with a superior ability for systematizing, understanding the rules that organize the structure and function of objects (Baron-Cohen & Belmonte, 2005). Consistent with this model, brain imaging studies show that people with autism have comparatively decreased activity in regions associated with understanding the minds of others and greater activation in regions related to basic object perception (Sigman, Spence & Wang, 2006).

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Although many people with ASD experience impairments throughout their lives that prevent them from having relationships and holding down a job, many go on to very successful careers. The renowned behavioural scientist and author Temple Grandin (2006) has written of her personal experience with autism. She was diagnosed with autism at age 3, started learning to talk late, and then suffered teasing for odd habits and “nerdy” behaviour. Fortunately, she developed ways to cope and found a niche through her special talent—the ability to understand animal behaviour (Sacks, 1996). She is now a Professor of Animal Science at Colorado State University; a celebrated author of books such as Animals in Translation; a designer of animal handling systems used widely in ranching, farming, and zoos; and the central character in a movie (starring Claire Danes) based on her life. Temple Grandin’s story lets us know that there are happy endings. Overall, those diagnosed with ASD as children have highly variable trajectories, with some achieving normal or better-than-normal functioning and others struggling with profound disorder. Autism is a childhood disorder that in adulthood can turn out many ways (see the Hot Science box).

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Chances are you have had the experience of being distracted during a lecture or while reading one of your other textbooks. We all have trouble focusing from time to time. Far beyond normal distraction, attention-deficit/hyperactivity disorder (ADHD), is a persistent pattern of severe problems with inattention and/or hyperactivity or impulsiveness that cause significant impairments in functioning. This is quite different than occasional mind wandering or bursts of activity. Meeting criteria for ADHD requires having multiple symptoms of inattention (e.g., persistent problems with sustained attention, organization, memory, following instructions), hyperactivity–impulsiveness (e.g., persistent difficulties with remaining still, waiting for a turn, not interrupting others), or both. Most children experience some of these behaviours at some point, but to meet criteria for ADHD, a child has to have many of these behaviours for at least 6 months in at least two settings (e.g., home and school) to the point where they impair the child’s ability to perform at school or get along at home.

Approximately 10 percent of boys and 4 percent of girls meet criteria for ADHD (Polanczyk et al., 2007). The DSM–5 requires that symptoms of ADHD be present before the age of 12 in order to meet criteria for this disorder. As you can imagine, children and adolescents with ADHD often struggle in the classroom. One recent study of 500 people with ADHD found that about half had a C average or lower, and about one-third were in special classes (Biederman et al., 2006). For a long time ADHD was thought of as a disorder that affects only children and adolescents and that people “age out” of the disorder. However, we now know that in many instances this disorder persists into adulthood. The same symptoms are used to diagnose both children and adults (e.g., children with ADHD may struggle with attention and concentration in the classroom, whereas adults may experience the same problems in meetings). Approximately 4 percent of adults meet criteria for ADHD, and adults with this disorder are more likely to be male, divorced, and unemployed—and most did not receive any treatment for their ADHD (Kessler, Adler, et al., 2006). Unfortunately, most people still think of this as a disorder of childhood and do not realize that adults can suffer from ADHD as well, which could be why so few adults with ADHD receive treatment, and why the disorder often wreaks havoc on job performance and relationships.

Because ADHD, like most disorders, is defined by the presence of a wide range of symptoms, it is unlikely that it emerges from one single cause or dysfunction. The exact cause of ADHD is not known, but there are some promising leads. Genetic studies suggest that there is a strong biological influence and estimate that the heritability of ADHD is 76 percent (Faraone et al., 2005). Brain imaging studies suggest that those with ADHD have smaller brain volumes (Castellanos et al., 2002) as well as structural and functional abnormalities in frontosubcortical networks associated with attention and behavioural inhibition (Makris et al., 2009). The good news is that current drug treatments for ADHD are effective and appear to decrease the risk of later psychological and academic problems (Biederman et al., 2009).

Michael is an 8-year-old boy whose mother brought him into a local clinic because his behaviour had been getting progressively out of control and his parents and teachers were no longer able to control him. Although Michael’s two older brothers and little sisters got along perfectly fine at home and at school, Michael had always gotten into trouble. At home he routinely bullied his siblings, threw glasses and dishes at family members, and on numerous occasions punched and kicked his parents. Outside of the house, Michael had been getting into trouble for stealing from the local store, yelling at his teacher, and spitting at the principal of his school. The last straw came when Michael’s parents found him trying to set fire to his bedspread one night. They tried punishing him by taking away his toys, restricting his privileges, and trying to encourage him with a sticker chart, but nothing seemed to change his behaviour.

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Conduct disorder is a condition in which a child or adolescent engages in a persistent pattern of deviant behaviour involving aggression to people or animals, destruction of property, deceitfulness or theft, or serious rule violations. Approximately 9 percent of people in the United States report a lifetime history of conduct disorder (12 percent of boys and 7 percent of girls) (Nock et al., 2006). Statistics for Canada are not available, but the rate is probably similar. The rate of 1 in 11 children may seem a bit high, but approximately 40 percent of those with conduct disorder have, on average, only 3 symptoms that cluster into one of three areas: rule breaking, theft/deceit, or aggression toward others. The other 60 percent have more symptoms, on average 6 to 8 of the 15 defined symptoms, with problems in many more areas and a much higher risk of having other mental disorders later in life (Nock et al., 2006).

Meeting criteria for conduct disorder requires having any 3 of the 15 symptoms of conduct disorder. This means there are approximately 32 000 different combinations of symptoms that could lead to a diagnosis, which makes those with conduct disorder a pretty diverse group. This diversity makes it difficult to pin down the causes of conduct disorder. One thing that seems clear is that a wide range of genetic, biological, and environmental factors interact to produce this disorder. Indeed, risk factors for conduct disorder include maternal smoking during pregnancy, exposure to abuse and family violence during childhood, affiliation with deviant peer groups, and the presence of deficits in executive functioning (e.g., decision making, impulsiveness) (Boden et al., 2010; Burke et al., 2002). Researchers currently are attempting to better understand the pathways through which inherited genetic factors interact with environmental stressors (e.g., childhood adversities) to create characteristics in brain structure and function (e.g., reduced activity in brain regions associated with planning and decision making) that interact with environmental factors (e.g., affiliation with deviant peers) to lead to the behaviours that are characteristic of conduct disorder. Not surprisingly, conduct disorder tends to co-occur with other disorders characterized by problems with decision making and impulsiveness, such as ADHD, substance use disorders, and antisocial personality disorder, which is described in more detail in the next section.

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