Neurodevelopmental disorders are a group of disabilities in the functioning of the brain that emerge at birth or during very early childhood and affect the individual’s behavior, memory, concentration, and/or ability to learn. As you read at the beginning of this chapter, many of the disorders first displayed during childhood subside as the person ages. However, the neurodevelopmental disorders often have a significant impact throughout the person’s life. For example, at least half of those with attention-deficit/hyperactivity disorder, one of the neurodevelopmental disorders, carry some version of their disorder with them into adulthood. Moreover, the vast majority of those with autism spectrum disorder and intellectual disability, two other neurodevelopmental disorders, continue to display the symptoms of their disorders in largely unchanged form throughout adulthood.

Researchers have investigated each of these disorders extensively. In addition, although this was not always so, clinicians now have a range of treatment approaches that can make a major difference in the lives of people with these problems.

Children with attention-deficit/hyperactivity disorder (ADHD) have great difficulty attending to tasks, or behave overactively and impulsively, or both (APA, 2013) (see Table 14.5 below). ADHD often appears before the child starts school, as with Ricky, one of the boys we met at the beginning of this chapter. Steven is another child whose symptoms began very early in life:

The symptoms of ADHD often feed into one another. Children who have trouble focusing attention may keep turning from task to task until they end up trying to run in several directions at once. Similarly, children who move constantly may find it hard to attend to tasks or show good judgment. In many cases, one of these symptoms stands out much more than the other. About half of the children with ADHD also have learning or communication problems; many perform poorly in school; a number have difficulty interacting with other children; and about 80 percent misbehave, often quite seriously (Mash & Wolfe, 2015; Goldstein, 2011). It is also common for these children to have anxiety or mood problems (Humphreys et al., 2015; Tsang et al., 2015).

Around 5 percent of all children display ADHD at any given time, as many as 70 percent of them boys (APA, 2013; Merikangas et al., 2011). The disorder usually persists throughout childhood. Many children show a marked lessening of symptoms as they move into mid-adolescence, but as many as 60 percent of affected children continue to have ADHD as adults (Weyandt et al., 2014). The symptoms of restlessness and overactivity are not usually as pronounced in adult cases.

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ADHD is a difficult disorder to assess properly (Batstra et al., 2014). Ideally, the child’s behavior should be observed in several environments (school, home, with friends) because the symptoms of hyperactivity and inattentiveness must be present across multiple settings in order for ADHD to be diagnosed (Burns et al., 2014; APA, 2013). Because children with ADHD often give poor descriptions of their symptoms, it is important to obtain reports of the child’s symptoms from his or her parents and teachers. And, finally, although diagnostic interviews, ratings scales, and psychological tests can be helpful in the assessment of ADHD, studies suggest that many children receive their diagnosis from pediatricians or family physicians rather than mental health professionals and that at most one-third of such diagnoses are based on psychological or educational testing (Millichap, 2010).

What Are the Causes of ADHD? Today’s clinicians generally consider ADHD to have several interacting causes. Biological factors have been identified in many cases, particularly abnormal activity of the neurotransmitter dopamine and abnormalities in the striatal region of the brain (Advokat et al., 2014; Hale et al., 2010). The disorder has also been linked to high levels of stress and to family dysfunctioning (Montejo et al., 2015; Rapport et al., 2008). In addition, sociocultural theorists have noted that ADHD symptoms and a diagnosis of ADHD may themselves create social problems and produce additional symptoms in the child. That is, children who are hyperactive tend to be viewed negatively by their peers and by their parents, and they often view themselves negatively as well (Martin, 2014; Chandler, 2010).

How Is ADHD Treated? Almost 80 percent of all children and adolescents with ADHD receive treatment (Winter & Bienvenu, 2011). There is, however, disagreement in the field about which kind of treatment is most effective. The most commonly used approaches are drug therapy, behavioral therapy, or a combination of the two (Sibley et al., 2014).

Millions of children and adults with ADHD are currently treated with methylphenidate, a stimulant drug that has been available for decades, or with certain other stimulants. Although a variety of manufacturers now produce methylphenidate, the drug continues to be known to the public by its most famous trade name, Ritalin. As researchers have confirmed Ritalin’s quieting effect on children with ADHD and its ability to help them focus, solve complex tasks, perform better at school, and control aggression, use of the drug has increased enormously—according to some estimates, at least a threefold increase since 1990 alone (Mash & Wolfe, 2015; Sibley et al., 2014). Today, an estimated 2.2 million children in the United States, 3 percent of all schoolchildren, regularly take Ritalin or other stimulant drugs for ADHD. Collectively, the drugs are the most common treatment for the disorder.

Although widely used, Ritalin and other stimulant drugs have raised certain concerns. First, many clinicians worry about the possible long-term effects of the drugs (Berg et al., 2014; Waugh, 2013), and others question whether the favorable findings of the drug studies (most of which have been done on white American children) are applicable to children from minority groups. Second, investigations indicate that ADHD is overdiagnosed in the United States, so many children who are receiving the stimulants may, in fact, not really be in need of them (Batstra et al., 2014; Rapport et al., 2008).

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Behavioral therapy has been used to help treat many people with ADHD. Parents and teachers learn how to reward children for their attentiveness or self-control, often by using a token economy program (Coates et al., 2015; DuPaul et al., 2011). Such operant conditioning treatments have been helpful for a number of children, especially when combined with stimulant drug therapy (Sibley et al., 2014; Dendy, 2011). Combining behavioral and drug therapies is also desirable because, according to research, children who receive both treatments require lower levels of medication, meaning, of course, that they are less subject to the medication’s possible side effects (Hoza et al., 2008).

Multicultural Factors and ADHD Throughout this book, you have seen that race often affects how people are diagnosed and treated for various psychological disorders. Thus, you should not be totally surprised that race also seems to come into play with regard to ADHD.

A number of studies indicate that African American and Hispanic American children with significant attention and activity problems are less likely than white American children with similar symptoms to be assessed for ADHD, receive a diagnosis of ADHD, or undergo treatment for it (Morgan et al., 2014; Bussing et al., 2005, 2003, 1998). Moreover, among those who do receive such a diagnosis and treatment, children from racial minorities are less likely than white American children to be treated with stimulant drugs or a combination of stimulants and behavioral therapy—the interventions that seem to be of most help to those with ADHD (Pham et al., 2010). Finally, among those children who do receive stimulant drug treatment for ADHD, children from racial minorities are less likely than white American children to receive the promising (but more expensive) long-acting stimulant drugs that have been developed in recent years (Sugrue et al., 2014; Cooper, 2004).

In part, these racial differences are tied to economic factors. Studies consistently show that poorer children are less likely than wealthier ones to be identified as having ADHD and are less likely to receive effective treatment, and racial minority families have, on average, lower incomes and weaker insurance coverage than white American families. Some clinical theorists further believe that social bias and stereotyping may contribute to the racial differences in diagnosis and treatment. They argue that our society often views the symptoms of ADHD as medical problems when exhibited by white American children but as indicators of poor parenting, lower IQ, substance use, or violence when displayed by African American and Hispanic American children (Duval-Harvey & Rogers, 2010; Kendall & Hatton, 2002). This notion has been supported by the research finding that, all symptoms being equal, teachers and parents are more likely to conclude that overactive white American children have ADHD but that overactive African American or Hispanic American children have other kinds of difficulties (Hillemeier et al., 2007; Raymond, 1997; Samuel et al., 1997).

Whatever the reason—economic disadvantage, social bias, racial stereotyping, or other factors—it appears that children from racial minority groups are less likely to receive a proper ADHD diagnosis and treatment. While many of today’s theorists correctly raise the possibility that ADHD may be generally overdiagnosed, it is important to recognize that children from certain segments of society may, in fact, be underdiagnosed and undertreated.

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Autism spectrum disorder, a pattern first identified by psychiatrist Leo Kanner in 1943, is marked by extreme unresponsiveness to other people, severe communication deficits, and highly rigid and repetitive behaviors, interests, and activities (APA, 2013) (see Table 14.6). These symptoms appear early in life, typically before 3 years of age. Just a few decades ago, the disorder seemed to affect around 1 out of every 2,000 children. However, in recent years there has been a steady increase in the number of children diagnosed with autism spectrum disorder, and it now appears that as many as 1 in 68 children display this pattern (CDC, 2015, 2014). Jennie is one such child:

Around 80 percent of all cases of autism spectrum disorder occur in boys. As many as 90 percent of children with the disorder remain significantly disabled into adulthood. They have great difficulty maintaining employment, performing household tasks, and leading independent lives (Sicile-Kira, 2014). Even the highest-functioning adults with autism typically have problems with closeness and empathy and have restricted interests and activities.

The individual’s lack of responsiveness and social reciprocity—extreme aloofness, lack of interest in other people, low empathy, and inability to share attention with others—has long been considered a central feature of autism. Like Jennie, children with autism typically do not reach for their parents during infancy. Instead they may arch their backs when they are held and appear not to recognize or care about those around them. In a similar vein, unlike other children of the same age, autistic children typically do not include others in their play and do not represent social experiences when they are playing; they often fail to see themselves as others see them and have no desire to imitate or be like others (Bodison, 2015; Boyd et al., 2011).

Communication problems take various forms in autism spectrum disorder. Many autistic people have great difficulty understanding speech or using language for conversational purposes. In fact, like Jennie, half fail to speak or develop effective language skills (Paul & Gilbert, 2011). Those who do talk may have rigid and repetitious speech patterns. One of the most common speech peculiarities is echolalia, the exact echoing of phrases spoken by others. The individuals repeat the words, but with no sign of understanding or intent of communicating. Another speech oddity is pronominal reversal, or confusion of pronouns—for example, the use of “you” instead of “I.” When hungry, a child with autism spectrum disorder might say, “Do you want dinner?”

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The nonverbal behaviors of these individuals are often at odds with their efforts at verbal communication. They may not, for example, use a proper tone when talking. It is also common for autistic persons to show few or no facial expressions or body gestures. In addition, a number are unable to maintain proper eye contact during interactions. Recall, for example, that Jennie “rarely made eye contact with anyone.”

Autistic people also display a wide range of highly rigid and repetitive behaviors, interests, and activities that extend beyond speech patterns. Typically they become very upset at minor changes in objects, persons, or routines and resist any efforts to change their own repetitive behaviors. Recall that Jennie was most aggressive when introduced to something or someone new.

Similarly, some children with the disorder react with tantrums if a parent wears an unfamiliar pair of glasses, a chair is moved to a different part of the room, or a word in a song is changed. Kanner (1943) labeled such reactions a perseveration of sameness. Many also become strongly attached to particular objects—plastic lids, rubber bands, buttons, water. They may collect these objects, carry them, or play with them constantly. Some are fascinated by movement and may watch spinning objects, such as fans, for hours.

People with autism may display motor movements that are unusual, rigid, and repetitive. They may jump, flap their arms, twist their hands and fingers, rock, walk on their toes, spin, and make faces. These acts are called self-stimulatory behaviors. Some autistic individuals also perform self-injurious behaviors, such as repeatedly lunging into or banging their head against a wall, pulling their hair, or biting themselves (Aman & Farmer, 2011).

The symptoms of autism spectrum disorder suggest a very disturbed and contradictory pattern of reactions to stimuli (see PsychWatch below). Sometimes the individuals seem overstimulated by sights and sounds and appear to be trying to block them out (called hyperreactivity), while at other times they seem understimulated and appear to be performing self-stimulatory actions (called hyporeactivity). They may, for example, fail to react to loud noises yet turn around when they hear soda being poured.

What Are the Causes of Autism Spectrum Disorder? A variety of explanations have been offered for autism spectrum disorder. This is one disorder for which sociocultural explanations have probably been overemphasized. In fact, such explanations initially led investigators in the wrong direction. More recent work in the psychological and biological spheres has persuaded clinical theorists that cognitive limitations and brain abnormalities are the primary causes of this disorder.

SOCIOCULTURAL CAUSES At first, theorists thought that family dysfunction and social stress were the primary causes of autism spectrum disorder. When he first identified this disorder, for example, Kanner argued that particular personality characteristics of the parents created an unfavorable climate for development and contributed to the disorder (Kanner, 1954, 1943). He saw these parents as very intelligent yet cold—“refrigerator parents.” These claims had enormous influence on the public and on the self-image of the parents themselves, but research has totally failed to support a picture of rigid, cold, rejecting, or disturbed parents (Sicile-Kira, 2014; Vierck & Silverman, 2011).

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Similarly, some clinical theorists have proposed that a high degree of social and environmental stress is a factor in the disorder. Once again, however, research has not supported this notion. Investigators who have compared autistic children with nonautistic children have found no differences in the rate of parental death, divorce, separation, financial problems, or environmental stimulation (Landrigan, 2011).

PSYCHOLOGICAL CAUSES According to certain theorists, people with autism spectrum disorder have a central perceptual or cognitive disturbance that makes normal communication and interactions impossible. One influential explanation holds that those with the disorder fail to develop a theory of mind—an awareness that other people base their behaviors on their own beliefs, intentions, and other mental states, not on information that they have no way of knowing (Begeer et al., 2015; Kimhi et al., 2014).

By 3 to 5 years of age, most normal children can take the perspective of another person into account and use it to anticipate what the person will do. In a way, they learn to read others’ minds. Let us say, for example, that we watch Jessica place a marble in a container and then we observe Frank move the marble to a nearby room while Jessica is taking a nap. We know that later Jessica will search first in the container for the marble because she is not aware that Frank moved it. We know that because we take Jessica’s perspective into account. A normal child would also anticipate Jessica’s search correctly. An autistic child would not. He or she would expect Jessica to look in the nearby room because that is where the marble actually is. Jessica’s own mental processes would be unimportant to the person.

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Studies show that people with autism spectrum disorder do indeed have this kind of “mind-blindness,” although they are not the only kinds of individuals with this limitation (Loukusa et al., 2014). They thus have great difficulty taking part in make-believe play, using language in ways that include the perspectives of others, developing relationships, or participating in human interactions. Why do autistic people have this and other cognitive limitations? Some theorists believe that they suffered early biological problems that prevented proper cognitive development.

BIOLOGICAL CAUSES For years researchers have tried to determine what biological abnormalities might cause theory-of-mind deficits and the other features of autism spectrum disorder. They have not yet developed a complete biological explanation, but they have uncovered some promising leads. First, examinations of the relatives of autistic people keep suggesting a genetic factor in this disorder (Egawa et al., 2015). The prevalence of autism among their siblings, for example, is as high as 1 per 10, a rate much higher than the general population’s (Risch et al., 2014). Moreover, the prevalence of autism among the identical twins of autistic people is 60 percent.

Some studies have also linked autism spectrum disorder to prenatal difficulties or birth complications (Reichenberg et al., 2011). For example, the chances of developing the disorder are higher when the mother had rubella (German measles) during pregnancy, was exposed to toxic chemicals before or during pregnancy, or had complications during labor or delivery.

Finally, researchers have identified specific biological abnormalities that may contribute to autism spectrum disorder. One line of research has pointed to the cerebellum (Mosconi et al., 2015; Pierce & Courchesne, 2002, 2001). Brain scans and autopsies show abnormal development in this brain area occurring early in the life of autistic people. Scientists have long known that the cerebellum coordinates movement in the body, but they now suspect that it also helps control a person’s ability to shift attention rapidly. It may be that people whose cerebellum develops abnormally will have great difficulty adjusting their level of attention, following verbal and facial cues, and making sense of social information—all key features of autism.

In a similar vein, neuroimaging studies indicate that many autistic children have increased brain volume and white matter and structural abnormalities in the brain’s limbic system, brain stem nuclei, and amygdala (Travers et al., 2015; Bauman, 2011). Many people with autism spectrum disorder also have reduced activity in the brain’s temporal and frontal lobes when they perform language and motor tasks (Taylor et al., 2014).

Given such findings, many researchers believe that this disorder may in fact have multiple biological causes (NINDS, 2015). Perhaps each of the relevant biological factors (genetic, prenatal, birth, and postnatal) can eventually lead to a common problem in the brain—a “final common pathway,” such as neurotransmitter abnormalities, that produces the cognitive problems and other features of the disorder.

Finally, because it has received so much attention over the past 20 years, it is worth mentioning a biological explanation for autism spectrum disorder that has not been borne out—the MMR vaccine theory. In 1998 a team of investigators published a study suggesting that a postnatal event—the vaccine for measles, mumps, and rubella (MMR vaccine)—might produce autistic symptoms in some children (Wakefield et al., 1998). The researchers suggested that for certain children, this vaccine, which is usually given to children between the ages of 12 and 15 months, produces an increase in the measles virus throughout the body which in turn causes the onset of a powerful stomach disease and, ultimately, autism spectrum disorder.

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However, virtually all research conducted since 1998 has argued against this theory (Taylor et al., 2014; Ahearn, 2010). First, epidemiological studies repeatedly have found that children throughout the world who receive the MMR vaccine have the same prevalence of autism as those who do not receive the vaccine. Second, according to research, children with autism do not have more measles viruses in their bodies than children without autism. Third, autistic children do not have the special stomach disease proposed by this theory. Finally, careful reexaminations of the original study have indicated that it was methodologically flawed and perhaps manipulated and that it actually failed to demonstrate any relationship between the MMR vaccine and the development of autism spectrum disorder (Lancet, 2010). Unfortunately, despite this clear refutation, many concerned parents now choose to withhold the MMR vaccine from their young children, leaving them highly vulnerable to diseases that can be extremely dangerous.

How Do Clinicians and Educators Treat Autism Spectrum Disorder? Treatment can help people with autism spectrum disorder adapt better to their environment, although no treatment yet known totally reverses the autistic pattern. Treatments of particular help are cognitive-behavioral therapy, communication training, parent training, and community integration. In addition, psychotropic drugs and certain vitamins have sometimes helped when combined with other approaches (Sicile-Kira, 2014; Ristow et al., 2011).

COGNITIVE-BEHAVIORAL THERAPY Behavioral approaches have been used in cases of autism for more than 35 years to teach new, appropriate behaviors, including speech, social skills, classroom skills, and self-help skills, while reducing negative, dysfunctional ones. Most often, the therapists use modeling and operant conditioning. In modeling, they demonstrate a desired behavior and guide autistic individuals to imitate it. In operant conditioning, they reinforce desired behaviors, first by shaping them—breaking them down so they can be learned step by step—and then rewarding each step clearly and consistently. With careful planning and execution, these procedures often produce new, more functional behaviors.

A pioneering, long-term study compared the progress of two groups of children with autism spectrum disorder (Lovaas, 2003, 1987; McEachin et al., 1993). Nineteen received intensive behavioral treatments, and 19 served as a control group. The treatment began when the children were 3 years old and continued until they were 7. By the age of 7, the behavioral group was doing better in school and scoring higher on intelligence tests than the control group. Many were able to go to school in regular classrooms. The gains continued into the research participants’ teenage years. Given the favorable findings of this and similar studies, many clinicians now consider early behavioral programs to be the preferred treatment for autism spectrum disorder (Boyd et al., 2014).

Therapies for people with autism spectrum disorder, particularly behavioral therapies, tend to provide the most benefit when they are started early in the children’s lives (Estes et al., 2015). Very young autistic children often begin with services at home, but ideally, by the age of 3 they attend special programs outside the home. A federal law lists autism spectrum disorder as 1 of 10 disorders for which school districts must provide a free education from birth to age 22, in the least restrictive or most appropriate setting possible. Typically, services are provided by education, health, or social service agencies until the children reach 3 years of age; then the department of education for each state determines which services will be offered.

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Given the recent increases in the prevalence of autism spectrum disorder, many school districts are now trying to provide education and training for autistic children in special classes that operate at the district’s own facilities (Iadarola et al., 2015). However, most school districts remain ill-equipped to meet the profound needs of students with autism. The most fortunate autistic students are sent by their school districts to attend special schools, where education and therapy are combined. At such schools, specially trained teachers help the children improve their skills, behaviors, and interactions with the world. Higher-functioning autistic students may eventually spend at least part of their school day returning to standard classrooms in their own school district (Hartford & Marcus, 2011).

COMMUNICATION TRAINING As you read earlier, even when given intensive behavioral treatment, half of the people with autism spectrum disorder remain speechless. To help address this, they are often taught other forms of communication, including sign language and simultaneous communication, a method combining sign language and speech. They may also learn to use augmentative communication systems, such as “communication boards” or computers that use pictures, symbols, or written words to represent objects or needs (Lerna et al., 2014; Prelock et al., 2011). A child may point to a picture of a fork to give the message “I am hungry,” for instance, or point to a radio for “I want music.” Recall, for example, the use of a “picture book” by Jennie, the child whose case introduced this section.

PARENT TRAINING Today’s treatment programs for autism spectrum disorder involve parents in a variety of ways. Behavioral programs, for example, often train parents so that they can use behavioral techniques at home (Bearss et al., 2015; Sicile-Kira, 2014). Instruction manuals for parents and home visits by teachers and other professionals are typically included in such programs. Research consistently has demonstrated that the behavioral gains produced by trained parents are often equal to or greater than those generated by teachers.

In addition to parent-training programs, individual therapy and support groups are becoming more available to help the parents of autistic children deal with their own emotions and needs (Clifford & Minnes, 2013; Hastings, 2008). A number of parent associations and lobbies also offer emotional support and practical help.

COMMUNITY INTEGRATION Many of today’s school-based and home-based programs for autism spectrum disorder teach self-help, self-management, and living, social, and work skills as early as possible to help the individuals function better in their communities. In addition, greater numbers of carefully run group homes and sheltered workshops are now available for teenagers and young adults with autism. These and related programs help those with autism become a part of their community; they also reduce the concerns of aging parents whose children will always need supervision.

Ed Murphy, aged 26, can tell us what it’s like to be considered “mentally retarded”:

For much of his life Ed was labeled mentally retarded and was educated and cared for in special institutions. During his adult years, clinicians discovered that Ed’s intellectual ability was in fact higher than had been assumed. In the meantime, however, he had lived the childhood and adolescence of a person labeled mentally retarded, and his statement reveals the kinds of difficulties often faced by people with this disorder.

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In DSM-5, the term “mental retardation” has been replaced by intellectual disability. This term is applied to a varied population, including children in institutional wards who rock back and forth, young people who work in special job programs, and men and women who raise and support their families by working at undemanding jobs. As many as 3 of every 100 people meet the criteria for this diagnosis (NLM, 2015; APA, 2013). Around three-fifths of them are male, and the vast majority display a mild level of the disorder.

People receive a diagnosis of intellectual disability (ID) when they display general intellectual functioning that is well below average, in combination with poor adaptive behavior (APA, 2013). That is, in addition to having a low IQ (a score of 70 or below), a person with ID has great difficulty in areas such as communication, home living, self-direction, work, or safety. The symptoms also must appear before the age of 18 (see Table 14.7).

Assessing Intelligence Educators and clinicians administer intelligence tests to measure intellectual functioning (see Chapter 3). These tests consist of a variety of questions and tasks that rely on different aspects of intelligence, such as knowledge, reasoning, and judgment. Having difficulty in just one or two of these subtests or areas of functioning does not necessarily reflect low intelligence (see PsychWatch on page 491). It is an individual’s overall test score, or intelligence quotient (IQ), that is thought to indicate general intellectual ability.

Many theorists have questioned whether IQ tests are indeed valid. Do they actually measure what they are supposed to measure? The correlation between IQ and school performance is rather high—around .50—indicating that many children with lower IQs do, as one might expect, perform poorly in school, while many of those with higher IQs perform better (Sternberg et al., 2001). At the same time, the correlation also suggests that the relationship is far from perfect. That is, a particular child’s school performance is often higher or lower than his or her IQ might predict. Moreover, the accuracy of IQ tests at measuring extremely low intelligence has not been evaluated adequately, so it is difficult to properly assess people with severe intellectual disability (AAIDD, 2013, 2010).

Intelligence tests also appear to be socioculturally biased, as you read in Chapter 3. Children reared in households at the middle and upper socioeconomic levels tend to have an advantage on the tests because they are regularly exposed to the kinds of language and thinking that the tests evaluate. The tests rarely measure the “street sense” needed for survival by people who live in poor, crime-ridden areas—a kind of know-how that certainly requires intellectual skills. Members of cultural minorities and people for whom English is a second language also often appear to be at a disadvantage in taking these tests.

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If IQ tests do not always measure intelligence accurately and objectively, then the diagnosis of intellectual disability also may be biased. That is, some people may receive the diagnosis partly because of test inadequacies, cultural differences, discomfort with the testing situation, or the bias of a tester.

Assessing Adaptive Functioning Diagnosticians cannot rely solely on a cutoff IQ score of 70 to determine whether a person suffers from intellectual disability. Some people with a low IQ are quite capable of managing their lives and functioning independently, while others are not. The cases of Brian and Jeffrey show the range of adaptive abilities.

Brian seems well adapted to his environment outside school. However, Jeffrey’s limitations are pervasive. In addition to his low IQ score, Jeffrey has difficulty meeting challenges at home and elsewhere. Thus a diagnosis of intellectual disability may be more appropriate for Jeffrey than for Brian.

Several scales have been developed to assess adaptive behavior. Here again, however, some people function better in their lives than the scales predict, while others fall short. Thus to properly diagnose intellectual disability, clinicians should probably observe the adaptive functioning of each individual in his or her everyday environment, taking both the person’s background and the community’s standards into account. Even then, such judgments may be subjective, as clinicians may not be familiar with the standards of a particular culture or community.

What Are the Features of Intellectual Disability? The most consistent feature of intellectual disability is that the person learns very slowly (Sturmey & Didden, 2014; AAIDD, 2013, 2010). Other areas of difficulty are attention, short-term memory, planning, and language. Those who are institutionalized with this disorder are particularly likely to have these limitations. It may be that the unstimulating environment and minimal interactions with staff in many institutions contribute to such difficulties. Traditionally, four levels of intellectual disability have been distinguished: mild (IQ 50–70), moderate (IQ 35–49), severe (IQ 20–34), and profound (IQ below 20).

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MILD ID Some 80 to 85 percent of all people with intellectual disability fall into the category of mild ID (IQ 50–70). This is sometimes called the “educable” level because the individuals can benefit from schooling and can support themselves as adults. Mild ID is not usually recognized until children enter school and are assessed there. They demonstrate rather typical language, social, and play skills, but they need assistance when under stress—a limitation that becomes increasingly apparent as academic and social demands increase. Interestingly, the intellectual performance of individuals with mild ID often seems to improve with age; some even seem to leave the label behind when they leave school, and they go on to function well in the community (Sturmey & Didden, 2014; Sturmey, 2008). Their jobs tend to be unskilled or semiskilled.

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Research has linked mild ID mainly to sociocultural and psychological causes, particularly poor and unstimulating environments during a child’s early years, inadequate parent–child interactions, and insufficient learning experiences (Sturmey & Didden, 2014; Sturmey, 2008). These relationships have been observed in studies comparing deprived and enriched environments. In fact, some community programs have sent workers into the homes of young children with low IQ scores to help enrich the environment there, and their interventions have often improved the children’s functioning. When continued, programs of this kind also help improve the person’s later performance in school and adulthood (Ramey et al., 2012; Ramey & Ramey, 2007, 2004, 1992).

Although sociocultural and psychological factors seem to be the leading causes of mild ID, at least some biological factors also may be operating. Studies suggest, for example, that a mother’s moderate drinking, drug use, or malnutrition during pregnancy may lower her child’s intellectual potential (Hart & Ksir, 2014). Malnourishment during a child’s early years also may hurt his or her intellectual development, although this effect can usually be reversed at least partly if a child’s diet is improved before too much time goes by.

MODERATE, SEVERE, AND PROFOUND ID Approximately 10 percent of those with intellectual disability function at a level of moderate ID (IQ 35–49). They typically receive their diagnosis earlier in life than do individuals with mild ID, as they demonstrate clear deficits in language development and play during their preschool years. By middle school they further show significant delays in their acquisition of reading and number skills and adaptive skills. By adulthood, however, many individuals with moderate ID manage to develop a fair degree of communication skill, learn to care for themselves, benefit from vocational training, and can work in unskilled or semiskilled jobs, usually under supervision. Most also function well in the community if they have supervision (AAIDD, 2013, 2010).

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Approximately 3 to 4 percent of people with intellectual disability display severe ID (IQ 20–34). They typically demonstrate basic motor and communication deficits during infancy. Many also show signs of neurological dysfunction and have an increased risk for brain seizure disorder. In school, they may be able to string together only two or three words when speaking. They usually require careful supervision, profit somewhat from vocational training, and can perform only basic work tasks in structured and sheltered settings. Their understanding of communication is usually better than their speech. Most are able to function well in the community if they live in group homes, in community nursing homes, or with their families (AAIDD, 2013, 2010).

Around 1 to 2 percent of all people with intellectual disability function at a level of profound ID (IQ below 20). This level is very noticeable at birth or early infancy. With training, people with profound ID may learn or improve basic skills such as walking, some talking, and feeding themselves. They need a very structured environment, with close supervision and considerable help, including a one-to-one relationship with a caregiver, in order to develop to the fullest (AAIDD, 2013, 2010).

Severe and profound levels of intellectual disability often appear as part of larger syndromes that include severe physical handicaps. The physical problems are often even more limiting than the individual’s low intellectual functioning and in some cases can be fatal.

What Are the Biological Causes of Intellectual Disability? As you read earlier, the primary causes of mild ID are environmental, although biological factors may also be operating in many cases. In contrast, the main causes of moderate, severe, and profound ID are biological, although people who function at these levels also are strongly affected by their family and social environment (Sturmey & Didden, 2014; Fletcher, 2011). The leading biological causes of intellectual disability are chromosomal abnormalities, metabolic disorders, prenatal problems, birth complications, and childhood diseases and injuries.

CHROMOSOMAL CAUSES The most common of the chromosomal disorders that lead to intellectual disability is Down syndrome, named after Langdon Down, the British physician who first identified it. Down syndrome occurs in around 1 of every 1,000 live births, but the rate increases significantly when the mother’s age is over 35. Many older expectant mothers are now encouraged to undergo prenatal testing during the early months of pregnancy to identify Down syndrome and other chromosomal abnormalities.

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People with Down syndrome may have a small head, flat face, slanted eyes, high cheekbones, and, in some cases, protruding tongue. The latter may affect their ability to pronounce words clearly. They are often very affectionate with family members but in general display the same range of personality characteristics as people in the general population.

Several types of chromosomal abnormalities may cause Down syndrome (NICHD, 2015). The most common type (94 percent of cases) is trisomy 21, in which the person has three free-floating 21st chromosomes instead of two. Most people with Down syndrome range in IQ from 35 to 55. The individuals appear to age early, and many even show signs of neurocognitive decline as they approach 40 (Powell et al., 2014; Lawlor et al., 2001). It may be that Down syndrome and early neurocognitive decline often occur together because the genes that produce them are located close to each other on chromosome 21 (Rohn et al., 2014; Lamar et al., 2011).

Fragile X syndrome is the second most common chromosomal cause of intellectual disability. Children born with a fragile X chromosome (that is, an X chromosome with a genetic abnormality that leaves it prone to breakage and loss) generally display mild to moderate degrees of intellectual dysfunctioning, language impairments, and, in some cases, behavioral problems (Hahn et al., 2015; Hagerman, 2011). Typically, they are shy and anxious.

METABOLIC CAUSES In metabolic disorders, the body’s breakdown or production of chemicals is disturbed. The metabolic disorders that affect intelligence and development are typically caused by the pairing of two defective recessive genes, one from each parent. Although one such gene would have no influence if it were paired with a normal gene, its pairing with another defective gene leads to major problems for the child.

The most common metabolic disorder to cause intellectual disability is phenylketonuria (PKU), which strikes 1 of every 14,000 children. Babies with PKU appear normal at birth but cannot break down the amino acid phenylalanine. The chemical builds up and is converted into substances that poison the system, causing severe intellectual dysfunction and several other symptoms (NICHD, 2015; Waisbren, 2011). Today infants can be screened for PKU, and if started on a special diet before 3 months of age, they may develop normal intelligence.

Children with Tay-Sachs disease, another metabolic disorder resulting from a pairing of recessive genes, progressively lose their mental functioning, vision, and motor ability over the course of two to four years, and eventually die. One of every 30 persons of Eastern European Jewish ancestry carries the recessive gene responsible for this disorder, so that 1 of every 900 Jewish couples is at risk for having a child with Tay-Sachs disease.

PRENATAL AND BIRTH-RELATED CAUSES As a fetus develops, major physical problems in the pregnant mother can threaten the child’s prospects for a normal life (AAIDD, 2013, 2010; Bebko & Weiss, 2006). When a pregnant woman has too little iodine in her diet, for example, her child may be born with cretinism, also called severe congenital hypothyroidism, marked by an abnormal thyroid gland, slow development, intellectual disability, and a dwarflike appearance. This condition is rare today because the salt in most diets now contains extra iodine. Also, any infant born with this problem may quickly be given thyroid extract to bring about normal development.

Other prenatal problems may also cause intellectual disability. As you saw in Chapter 10, children whose mothers drink too much alcohol during pregnancy may be born with fetal alcohol syndrome, a group of very serious problems that includes mild to severe ID (Bakoyiannis et al., 2014; Hart & Ksir, 2014). In fact, a generally safe level of alcohol consumption during pregnancy has not been established by research. In addition, certain maternal infections during pregnancy—rubella (German measles) and syphilis, for example—may cause childhood problems that include intellectual disability.

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Birth complications also can lead to problems in intellectual functioning. A prolonged period without oxygen (anoxia) during or after delivery can cause brain damage and intellectual disability in a baby. In addition, although premature birth does not necessarily lead to long-term problems for children, researchers have found that some babies with a premature birth weight of less than 3.5 pounds display low intelligence (AAIDD, 2013, 2010; Taylor, 2010).

CHILDHOOD PROBLEMS After birth, particularly up to age 6, certain injuries and accidents can affect intellectual functioning and in some cases lead to intellectual disability. Poisonings, serious head injuries caused by accident or abuse, excessive exposure to X rays, and excessive use of certain drugs pose special dangers (AAIDD, 2013, 2010; Evans, 2006). For example, a serious case of lead poisoning from eating lead-based paints or inhaling high levels of automobile fumes can cause ID in children. Mercury, radiation, nitrite, and pesticide poisoning may do the same. In addition, certain infections, such as meningitis and encephalitis, can lead to intellectual disability if they are not diagnosed and treated in time (AAIDD, 2013, 2010; Durkin et al., 2000).

Interventions for People with Intellectual Disability The quality of life attained by people with intellectual disability depends largely on sociocultural factors: where they live and with whom, how they are educated, and the growth opportunities available at home and in the community. Thus intervention programs for these individuals try to provide comfortable and stimulating residences, a proper education, and social and economic opportunities. At the same time, the programs seek to improve the self-image and self-esteem of those with intellectual disability. Once these needs are met, formal psychological or biological treatments are also of help in some cases.

WHAT IS THE PROPER RESIDENCE? Until recent decades, parents of children with intellectual disability would send them to live in public institutions—state schools—as early as possible (Harris, 2010). These overcrowded institutions provided basic care, but residents were neglected, often abused, and isolated from society.

During the 1960s and 1970s, the public became more aware of these sorry conditions and, as part of the broader deinstitutionalization movement (see Chapter 12), demanded that many people with intellectual disability be released from the state schools (Harris, 2010). In many cases, the releases were done without adequate preparation or supervision. Like people with schizophrenia who were suddenly deinstitutionalized, those with intellectual disability were virtually dumped into the community. Often they failed to adjust and had to be institutionalized once again.

Since that time, reforms have led to the creation of small institutions and other community residences (group homes, halfway houses, local branches of larger institutions, and independent residences) that teach self-sufficiency, devote more staff time to patient care, and offer educational and medical services. Many of these settings follow the principles of normalization first started in Denmark and Sweden—they attempt to provide living conditions similar to those enjoyed by the rest of society; flexible routines; and normal developmental experiences, including opportunities for self-determination, sexual fulfillment, and economic freedom (Merrick et al., 2014; Hemmings, 2010).

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Today the vast majority of children with intellectual disability live at home rather than in an institution. During adulthood and as their parents age, however, some people with intellectual disability require levels of assistance and opportunities that their families are unable to provide. A community residence becomes an appropriate alternative for them. Most people with intellectual disability, including almost all with mild ID, now spend their adult lives either in the family home or in a community residence (Sturmey & Didden, 2014; Sturmey, 2008).

WHICH EDUCATIONAL PROGRAMS WORK BEST? Because early intervention seems to offer such great promise, educational programs for people with intellectual disability may begin during the earliest years. The appropriate education depends on the person’s level of functioning. Educators hotly debate whether special classes or mainstreaming is most effective once the children enter school (McKenzie et al., 2013; Hardman et al., 2002). In special education, children with intellectual disability are grouped together in a separate, specially designed educational program. In contrast, in mainstreaming, or inclusion, they are placed in regular classes with students from the general school population. Neither approach seems consistently superior. It may well be that mainstreaming is better for some areas of learning and for some children and that special classes are better for others.

Teacher preparedness is another factor that may play into decisions about mainstreaming and special education classes. Many teachers report feeling inadequately prepared to provide training and support for children with intellectual disability, especially children who have additional problems. Brief training courses for teachers appear to address such concerns (Hallahan et al., 2014; Campbell et al., 2003).

Teachers who work with students with intellectual disability often use operant conditioning principles to improve their students’ self-help, communication, social, and academic skills (Sturmey & Didden, 2014; Sturmey, 2008; Ardoin et al., 2004). They break learning tasks down into small steps, giving positive reinforcement for each increment of progress. Additionally, many institutions, schools, and private homes have set up token economy programs—the operant conditioning programs that have also been used to treat institutionalized patients who have schizophrenia.

WHEN IS THERAPY NEEDED? Like anyone else, people with intellectual disability sometimes have emotional and behavioral problems. Around 30 percent or more have a psychological disorder other than intellectual disability (Sturmey & Didden, 2014; Bouras & Holt, 2010). Furthermore, some suffer from low self-esteem, interpersonal problems, and difficulties adjusting to community life. These problems are helped to some degree by either individual or group therapy. Large numbers of people with intellectual disability also take psychotropic medications (Sturmey & Didden, 2014). Many clinicians argue, however, that too often the medications are used simply for the purpose of making the individuals easier to manage.

HOW CAN OPPORTUNITIES FOR PERSONAL, SOCIAL, AND OCCUPATIONAL GROWTH BE INCREASED? People need to feel effective and competent in order to move forward in life. Those with intellectual disability are most likely to feel effective and competent if their communities allow them to grow and to make many of their own choices. Denmark and Sweden, where the normalization movement began, have again been leaders in this area, developing youth clubs that encourage those with intellectual disability to take risks and function independently. The Special Olympics program has also encouraged those with intellectual disability to be active in setting goals, to participate in their environment, and to interact socially with others (Crawford et al., 2015; Marks et al., 2010).

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Socializing, sex, and marriage are difficult issues for people with intellectual disability and their families, but with proper training and practice, they usually can learn to use contraceptives and carry out responsible family planning. National advocacy organizations and a number of clinicians currently offer guidance in these matters, and some have developed dating skills programs (AAIDD, 2013, 2010, 2008; Segal, 2008).

Some states restrict marriage for people with intellectual disability. These laws are rarely enforced, though, and in fact many people with mild ID marry. Contrary to popular myths, the marriages can be very successful. And although some may be incapable of raising children, many are quite able to do so, either on their own or with special help and community services (Sturmey & Didden, 2014; AAIDD, 2013, 2010; Sturmey, 2008).

Finally, adults with intellectual disability—whatever the severity—need the personal and financial rewards that come with holding a job (AAIDD, 2013, 2010; Kiernan, 2000). Many work in sheltered workshops, protected and supervised workplaces that train them at a pace and level tailored to their abilities. After training in the workshops, many with mild or moderate ID move on to hold regular jobs.

Although training programs for people with intellectual disability have improved greatly in quality over the past 35 years, there are too few of them. Consequently, most participants do not receive a complete range of educational and occupational training services. Additional programs are required so that more people with intellectual disability may achieve their full potential, as workers and as human beings.