The causes of learning disorders, while not well understood, are generally attributed to

HISTORICAL OVERVIEW

Learning disabilities were defined in U.S. federal law with the Learning Disabilities Act in 1969 to address the needs of these children who were not previously well served by the education system.10 The Association for Children with Learning Disabilities, formed by parents and educators and led by the psychologist Samuel Kirk, advocated for recognition of learning disabilities and access to special education services. Lyon and associates5 proposed that, as with many other advancements in fields of medicine, psychology, education, and public policy, systematic scientific inquiry into learning disabilities followed from the identification of real-world problems experienced by children and from public advocacy on their behalf.

Despite the mobilizing influence on research of the recognition of learning disabilities, the scientific basis of learning disabilities has historical roots in the neurology of acquired language disorders studied in the 1800s. In these studies of aphasia, specific deficits in the comprehension and production of language in the context of otherwise spared cognitive function were noted in adults with acquired brain lesions. These observations proved important with regard to one of the central features of learning disabilities: namely, that learning difficulties could result in selective rather than general cognitive deficits.11

In the late 1800s and early 1900s, cases of what today would be called reading disabilities were reported by neurologists who observed children and adults with no known brain injuries who could not read despite seemingly intact general cognitive abilities.12 In the 1920s, Samuel Orton, a neurologist, proposed that in children who could not read, development of left hemisphere dominance for language functions was delayed or had failed. He was the first to address the heterogeneity of learning disabilities as disorders that could specifically affect reading, writing, speech, comprehension, or motor skills.11 In collaboration with the linguist, Anne Gillingham, he devised intervention programs for children with reading difficulties, variants of which are still in use13 and undergoing evaluation as to their efficacy.5 Another important influence in the field of learning disabilities arose from studies in which investigators attempted to understand similarities in behavioral disorders such as hyperactivity in children with brain injuries and in children with no brain injury who had learning difficulties and normal intelligence. It was inferred that this latter group had minimal brain dysfunction.11

Several notions were common to these early conceptualizations of learning disability: namely, that there is a neurobiological basis for the learning difficulty; that there can be selective deficits rather than global retardation; and that processes that help or interfere with learning could be identified and remedied through interventions. The field of learning disabilities continues to be influenced by these conceptualizations, as discussed in the next section.

9.03.1 Introduction

Learning disabilities (LDs) are learning problems that specifically affect one or more skill areas, such as reading, writing, or social skills, in persons who appear to be otherwise normally skilled and educated. The best-known, and most common, type of LD is dyslexia, which is characterized by a singular inability to read in an otherwise competent person. Although learning disabilities may be acquired by adults or children as a result of brain trauma, they originate typically as a developmental disorder of childhood, where they are as common as they are seemingly intractable to treatment.

There are many different psychological disorders that might afflict us at some time during our childhood. Some are known and feared by parents mainly because of the extensive media coverage they receive, featuring their dramatic nature, attendant family trauma, and poor prognosis. Examples include severe mental retardation, autism, fragile-X, and Tourette's and Rett's disorders. But many parents are less aware of the two psychological disorders of childhood that are by far the most likely to intrude into their lives. These are LD and Attention deficit hyperactivity disorder (ADHD). Each of these disorders affects about one child in every 20 and their combined prevalence is probably higher than that of all the other childhood psychological disorders (Pennington, 1991). Moreover, because LD and ADHD have a significant comorbidity and because each can lead to a secondary expression of some symptoms of the other, they are often confused with one another.

This chapter primarily is concerned with learning disabilities of developmental origin, as expressed in school-aged children. However, some reference is made to life-span implications, comorbid conditions, and the effects of brain trauma. As is appropriate in a volume on clinical psychology, emphasis is placed on the main concerns of the clinician: identification, assessment, and treatment. As far as possible, in the interests of providing a consistent framework, these are placed in the context of a broad conceptualisation of the behavioral assessment model (Nelson & Hayes, 1986).

Classification

Learning disability is classified as mild (IQ 50–69), moderate (IQ 35–49), severe (IQ 20–34) or profound (IQ under 20). The division into these four groups is fairly arbitrary and there is a great deal of overlap between them. The spectrum of disability for the key areas of language skills, self care, mobility, academic achievement and ability to work are shown in Table 1.

Aetiology

The cause of mild learning disability is unknown in about half of cases. Many of these simply represent the lower end of the normal distribution of intelligence. With increasing severity of learning disability, the likelihood of finding a cause increases, with at least 80% of severe cases having some evidence of organic brain damage or disease. Some of the aetiological factors are listed in Figure 1.

It is clear that social factors also play a role in causing learning disability. It has been estimated that up to 5% of cases are due to child abuse, with many being a consequence of brain damage, occurring as a direct result of physical assaults, usually by the parents. Other forms of abuse also appear to have an impact on intellectual performance. Emotional abuse by cruel and neglectful parents who fail to provide a stimulating and nurturing environment for their child results in impaired psychological and physical development. Institutional care can have a similar effect.

Two of the more common clinical syndromes that cause learning disability are described below.

Mental illness and learning disability

About 40% of all children and adults with learning disability have a mental illness. The risk increases with the severity of the learning impairment. The presence of organic brain disease increases vulnerability to mental illness, but emotional factors also play an important role and must not be overlooked. Children with learning disability often have a sense of being a disappointment to their parents and different from other people. They may be isolated from their family and the community, stigmatised, bullied or abused. They may lack the skills to express their feelings of sadness or anger, and so these feelings will go unrecognised.

The commonest forms of mental illness found in children with learning disability are hyperkinetic disorder and conduct disorders. They are also at increased risk of exploitation and abuse.

In adults, schizophrenia, affective disorders, neurotic disorders and personality disorders are all found more frequently than in the general population. Diagnosis can present a challenge as they may not be able to describe their feelings and experiences, and when making a diagnosis it is often necessary to rely on behavioural changes such as psychomotor retardation, agitation or possible responses to hallucinations. It is sometimes worth giving a trial of medication if the diagnosis is uncertain. Treatment of mental illness is the same as for other patients, although psychological treatments will need to be delivered in a way that takes into account the patient's intellectual and social abilities.

Management of learning disability

Assessment begins with taking a full psychiatric and medical history from informants, usually the parents or other carers. The family history, achievement of developmental milestones and problem behaviours are particularly important. Mental state examination will rely largely upon observation of the patient's behaviour during the interview, although some will be able to participate in the interview. A thorough physical examination is required, remembering to assess vision and hearing. Finally, a developmental assessment is needed, including standardised measures of intelligence, language, motor performance and social skills. Other sources of information should be approached to complete the picture, including other doctors involved (GP, neurologist, paediatrician, etc.), the school and social services.

A treatment package might include the following:

Education in special schools. Assessment of needs should be completed by an educational psychologist.

Support for families. The birth of a child with learning disability can have a devastating effect on a family. The parents often experience grief over the loss of the anticipated perfect child and may have prolonged feelings of depression, guilt, shame or anger. The majority of families adjust well with support, although a few reject the child or become over-involved, and this can be associated with marital disharmony.

Recognition of emotional needs. As mentioned above, a person with learning disability may have powerful feelings of sadness or anger that they find difficult to express. Creative therapies, such as art or music, can allow communication through media other than words.

Employment opportunities. Many people with mild to moderate learning disability have practical skills that can be developed in sheltered workshops and supported work placements.

Institutional care is only needed for a minority. It is usually provided in small well-staffed community units near the child's family.

Case history 30

Jane is a 34-year-old woman with Down's syndrome and moderate learning disability. She has lived in a staffed hostel with four other residents for the past year since her elderly mother has been unwell and unable to care for her. Her mother died a month ago. She was told of this and went to the funeral but has not spoken of it again. Since then staff report she has been difficult to manage – eating little, irritable and lashing out at times and refusing to take part in her usual activities.

What is the cause of Jane's change of behaviour?

What could be done to help her?

Learning disability

In learning disability (mental retardation in ICD10) both intellectual and social functioning is impaired from early childhood

2–3% of the population have an IQ below 70 and half of these require input from specialist services

Brain disease or damage may occur as a result of genetic, intra-uterine, perinatal, postnatal and social factors

About 40% of all children and adults with learning disability have a mental illness

Etiology

Learning disability is not caused by one distinct etiology. The etiologies are difficult to ascertain because physiological, psychosocial, and environmental risk factors are all significant and variable in its development. Just as the types of learning disabilities are diffuse, so are their symptoms and causes. Also, just as an individual can have a single disability or multiple types simultaneously, so can there be multiple contributing factors to which the causes might be attributed.

The many types of learning disability are due to abnormalities in a child's cognitive development. Therefore, there are innumerable complications beginning in prenatal development that can occur and cause later abnormalities in a child's learning and development. As the brain develops in the fetus throughout pregnancy, disruptions can have minor or severe effects on the growing brain, depending on the gravity of the disruption and stage of development at which it occurs. Current leading theories support the hypothesis that subtle neurological abnormalities, present before birth, might be responsible. However, since three-fourths of those with this disability do not have a perinatal etiology, there must also exist other causal factors that contribute to its development.

Although there is no definite reason as to why some children develop a learning disability and others do not, there are some pre- and perinatal risk factors that point to possible etiologies. Studies have linked very preterm birth (<34 weeks), low birth weight, and very low birth weight with higher prevalences in childhood. Intrauterine exposure to alcohol, smoking, and drugs has also been linked to higher prevalences of developmental learning disabilities. Also, a higher risk in asphyxiated neonates (e.g., those whose umbilical cords were wrapped around their necks and who were temporarily cut off from oxygen) has been reported. Children born with neonatal neurological abnormalities are at higher risk. Furthermore, environmental toxins, such as cadmium and lead, are also being investigated as possible risk factors, although their effects are unclear and more comprehensive study is necessary.

Introduction

With learning disability (LD), the unexpected happens. The National Down Syndrome Cytogenetic Register (Morris 2008) reports that for England and Wales in 2000 there were 594 children born with Down syndrome, but in 2006 there were 749 – an increase of almost 15% and greater than the number (717) in 1989, the advent of prenatal screening. As Down syndrome is the commonest cause of LD where a cause is known, this has major implications for our future clinical practice.

The term ‘learning disability’ is unsatisfactory and a source of confusion – many other countries adopt the term mental retardation, and, in countries dominated by the classifications of DSM-IV, learning disability commonly refers to specific disorders of learning in those who do not necessarily have an intellectual impairment. The use of the terms ‘intellectual disability’ and ‘cognitive disability’ have become more common, but LD has been in widespread use since around the early 1990s, is enshrined in legislation (e.g. the Mental Health (Scotland) Act 2003), has passed into the language, and is the commonest term describing this complex intellectual and social condition that affects a substantial group of people. Indeed, it seems preferable to the very broad ‘learning difficulties’, which has attained prominence mainly through educational legislation. Older terms have become viewed as opprobrious, sometimes with good reason, sometimes largely because of the way society has treated and alienated people with LD. The history behind this nosology has been dealt with before (Rennie 2007). The important point to people with LD is not the naming, but whether they are recognised and respected as individuals in their own right. Cognitive disability does not diminish the moral status of any individual, no matter how severe. The arguments for (and against) the proposition that our common humanity insists that we should have respect for every individual with LD are addressed by Byrne (2000).

That LD is a descriptive term, not a disorder in itself, is the central theme of this chapter. We have made great progress in understanding the proximate causes behind the cognitive events, and can now often chart and study the different life trajectories of individuals with LD so as to make predictions about outcomes, susceptibilities and strengths, and design interventions. Each syndrome has features that not only distinguish it from others but also determine how these will change and develop over time. Leo Kanner (1964, in his History of the Care and Study of the Mentally Retarded) entitled a chapter ‘From homogeneity to heterogeneity’, noting the changes from the unitary idea of the early 19th century, which recognised only one specific type of disorder associated with LD (congenital hypothyroidism, then termed cretinism), through to a wide range of conditions including Down syndrome (DS) by the turn of the century.

In the last few years the number of conditions we know to be associated with learning disability has grown at an astounding rate, and behind this lie continuing advances in molecular genetics. Of particular importance is the recent discovery of extensive microdeletions and microduplications of chromosomes throughout the genome (copy number variation), and this will be described later, but more classic gene abnormalities are still being found in association with learning disability at a great rate, especially on the X chromosome. It is this extensive genetic variation and mutability that underpins the homeostatic and adaptive capacity of a species: Darwin's concepts seem increasingly valid over 150 years since their original presentation.

Mutations are essential and frequent, but many will not be adapted to the environment at any given time – and these are often deleterious. However, through cultural and social mechanisms we can alter environments, and previously severely incapacitating conditions have had their effects reduced, sometimes eliminated. Phenylketonuria (PKU; prevalence around 1:15 000) is a recessively inherited gene mutation on chromosome 12 that disrupts phenylalanine hydroxylase (PAH; converts phenylalanine to tyrosine), and was first described in the 1930s by Fölling in Norway. If untreated, toxic hyperphenylalanaemia occurs, and formerly PKU was associated in many with severe LD, epilepsy, microcephaly, and sometimes repeated self-injury. By the 1950s it was clear a low-phenylalanine diet had a marked effect: intellectual impairment was drastically reduced. This led to the development in the 1960s of a microbiological inhibition test by Guthrie which was widely adopted as one of the earliest perinatal screening programmes for a genetic disease. The rate of mutation for PKU has not decreased, however, but the disorder is now much more congruent with survival (Lindee 2000). We now know that the picture is more complex, and this is a paradigm for other genetic disorders affecting cognition (Scriver 2007). Human PAH gene has over 500 known mutations, genotype–phenotype correlations are often weak, implying modifiers such as the enzymes metabolising cofactors of PAH, and these events themselves are genetically determined. Some untreated patients achieve near normal intellectual outcome, an effect that may be due to variation in the transport of the phenylalanine across the blood–brain barrier. Thus from a simple mendelian disorder a complex multifactorial disorder has emerged, which is the paradigm for all disorders associated with intellectual impairment.

However, in spite of such promise, and exciting recent developments in other conditions such as Rett syndrome, most causes of LD are not open to such interventions; the aim is to maximise the person's potential within the restrictions that the disability imposes, and to detect and treat other coexisting conditions. Of these, psychiatric illness and behavioural disorders most concern the psychiatrist. When these arise in the setting of specific disorders, they are affected by the shared characteristics of the group, as well as by individual variations, including the person's previous history and experience. How the abnormalities affect developmental neurobiology is now much better understood, with disorders of neuronal division and patterning, neuronal migration and neuronal maturation, and examples of these are discussed below. In addition, infections, toxins and trauma still continue to take a huge worldwide toll, and their associations with LD are outlined.

Working with people with LD requires a broad knowledge base drawn from a diverse set of disciplines – child health, psychology, neurology, genetics and ageing – and there is a great need to understand the person beyond the simplistic concept of LD alone. This chapter focuses mainly on recent research; this is not to minimise the importance of the corpus of older work on which it is based, but space constraints mean that a focus has to be set. Nor can it be comprehensive: there are just too many conditions associated with LD. The older literature is covered in previous editions of this book (Muir 1998, 2004. In fact, older editions should be considered as companions to this one).

1 History of Learning Disabilities

The existence of learning disabilities has been documented for approximately 200 years. The origins of what are currently called learning disabilities began with early attempts to match functioning within certain areas of the brain to human behavior. Early physicians noticed that patients with certain types of brain injury experienced specific types of behavioral problems. Most relevant to learning disabilities were patients with injuries to the left hemispheres of their brains, who in many cases experienced problems such as slow, laborious speech and the inability to name objects or persons. In the late 1800s, a more specific set of cases was identified in which persons’ ability to speak and write remained intact, but their ability to comprehend spoken or written words was impaired. These conditions were termed word deafness and word blindness.

From these studies, during the early 20th century, physicians began to notice children and adults who experienced what was at the time considered to be defects in their ability to recognize words and letters, despite no obvious brain damage or injury. The inference was made that perhaps these individuals suffered from some sort of neurological disorder that mimicked the effects of people with brain damage. Moreover, a number of cases appeared to run in families, providing further evidence for a possible physical cause. The medical diagnosis for this condition was congenital word blindness.

Beginning around 1920, and building on this early work in medicine and neurology, a group of American pioneers including Samuel Orton, Grace Fernald, Marion Monroe, and Samuel Kirk began landmark work on understanding reading disabilities. While still clearly linked to foundations in medicine, reading disabilities were attacked by these researchers and clinicians as much from an educational perspective as from a clinical one. Indeed, some of these pioneer’s names have become synonymous with specific approaches to educational treatment for students with learning disabilities. For example, the Orton-Gillingham approach to treatment is a phonics-based, multisensory approach to instruction that uses the kinesthetic, auditory, and visual modalities for teaching decoding and spelling.

Parallel to developments in educational understanding of students with these disorders, additional work was being pursued between about 1920 and 1960 on the perceptual, perceptual-motor, and attentional abilities that often accompanied damage, injury, or dysfunction in persons’ brains. Physicians and psychologists such as Kurt Goldstein, Heinz Werner, Newell Kephart, and William Cruikshank conducted many research studies documenting deficits such as hyperactivity, perseveration, figure-ground confusion, and distractibility. Again, it was reasoned that if persons with documented damage to their brains exhibited perceptual and attentional problems, persons with presumed damage to these brain areas might be expected to have these problems as well.

It was between approximately 1960 and 1975 when the field of learning disabilities began emerging as a discipline unto itself. On April 6, 1963, another pioneer in the field of learning disabilities, Samuel Kirk, told a parent advocacy group for children with “perceptual handicaps” that “Recently, I have used the term ‘learning disability’ to describe a group of children who have disorders in development, in language, speech, reading and associated communication skills needed for social interaction. In this group, I do not include children who have sensory handicaps such as blindness or deafness, because we have methods of managing and training the deaf and blind. I also exclude from this group children who have generalized mental retardation” (Kirk, 1975, p. 9). Most educators attribute coinage of the term “learning disability” to Kirk. Moreover, some of the parents who heard Kirk’s speech in 1963 established the Association for Children with Learning Disabilities, which has now evolved into the Learning Disabilities Association of America. This organization is widely known as one of the most influential learning disabilities advocacy organization in the United States.

Introduction

The field of learning disabilities is confused by a range of terminology, used in various ways. In this article, we are referring to ‘global learning disabilities’, which are also called ‘mental retardation’ or ‘intellectual disability’ and affect all domains of thinking or intellectual functioning. Global learning disability needs to be distinguished from ‘specific learning disabilities’, also referred to as (specific) ‘learning difficulties’, where overall intellectual functioning is within the normal range but where specific abilities, most commonly reading, spelling, and mathematics, are operating at a level well below that predicted by overall ability. In this article, we shall use the terms mental retardation and learning disability interchangeably. There are three major classification systems for mental retardation: the American Association of Mental Retardation (AAMR), the Diagnostic and Statistical Manual (DSM), and the International Classification of Diseases (ICD) (Table 1). All three systems require the presence of not only globally reduced intellectual functioning but also significant impairment in adaptive functioning, that is, the ability to function in an age-appropriate way in areas of everyday life including learning, working, enjoying relationships, caring for oneself, and living independently.

Table 1. Classification of mental retardation

IQ, intelligence quotient.

Intellectual functioning is usually assessed by tests of cognitive functioning that produce a measure called the intelligence quotient (IQ). The IQ is measured by tests that examine thinking and knowledge in a range of areas. These areas usually include both verbal skills such as vocabulary knowledge, the ability to understand conceptual similarities between words and short-term (working) memory for verbal material, and nonverbal skills, such as completing puzzles, identifying missing parts of pictures and completing pictorial sequences. Because ability to complete such tasks changes with age, IQ tests are standardized across a range of ages. The IQ is the mental age divided by chronological age multiplied by 100, where mental age refers to the average score achieved by children of a certain chronological age. Therefore, an IQ of 100 is average. The scores on IQ tests are usually standardized to produce normally distributed scores with not only a mean of 100 but also a standard deviation of 15. People with mental retardation are expected to have IQs at the extreme low end of the normal distribution of IQ.

Degree or severity of mental retardation is largely classified by the IQ or an equivalent measure of intellectual ability. Mild mental retardation is defined in the ICD-10 and DSM-IV as IQ 50–69, moderate retardation as IQ 35–49, severe retardation as IQ 20–34, and profound retardation an IQ less than 20 (Table 1). IQ estimates are approximate and particularly difficult to measure precisely in more severely affected individuals. While the classification systems state that a criterion of impairment should also be met, none specify how this should be determined. Much of the epidemiological and biological research on mental retardation has collapsed the categories of moderate, severe, and profound retardation and referred to this group as having severe mental retardation.

General aspects

Learning impairment or disability is a term used for limitations in mental functioning and in skills such as communicating, self-care and social skills. In the USA, this same term is usually used to denote specific learning impairments, such as dyslexia, rather than impaired cognition.

The average intelligence quotient (IQ) score in the general population is 100. An IQ of less than 70 is the arbitrary dividing line that defines learning disability. Learning impairment affects as many as 3 out of every 100 people and is frequently the result of brain damage, often of unknown reason; defined causes are shown in Table 28.7.

Abstract

Specific learning disabilities (SLDs) are defined in relationship to (a) the changing historical context in which schools operate that made it necessary to identify and provide appropriate education for students with educationally handicapping conditions such as SLDs; (b) recent research on the biological basis and effective treatment for SLDs; (c) the differences between developmental disabilities (DDs) and SLDs; and (d) comorbid conditions that may or may not occur along with SLDs but are relevant to diagnosis and treatment if they do. Focus is on defining, diagnosing, and teaching students with dysgraphia, dyslexia, specific language disability (also referred to as oral and written language learning disability OWL LD), dyscalculia, and nonverbal learning disability (NVLD). Issues specific to educational management of SLDs during adolescence are discussed. The impact of SLDs, which may affect at least one in five adolescents, on the individual and society is considered. Current knowledge and unresolved issues regarding SLDs in adolescents are summarized and possible future trends are explored.

Prevalence

LDs are the most common condition for which school-age children receive special education services. According to the US Department of Education, 6.5 million children in the US received special education services during the most recent inquiry period (2008–09), and 38% of these students had specific LDs. Among children with LDs, RD is often said to be the most prevalent, although some studies suggest that MD is as common. RD is by far the most well studied of LDs. In general, prevalence rates for reading, writing, and mathematics LDs range from approximately 5% to 20%; more exact figures are difficult to establish due to variability in criteria, as well as study methods (e.g., self-report vs. direct assessment). Historically, LDs have been diagnosed more frequently in boys than girls; however, more recently, LD diagnoses in girls have increased, with research showing that prevalence rates among boys and girls are more comparable than once thought.