What are learning disorders?

Introduction

Learning disorders (LD) is a general term for clinical conditions that meet four diagnostic criteria, as specified by the fifth edition of the
Diagnostic and Statistical Manual of Mental Disorders (DSM-5), published in 2013 by the American Psychiatric Association. Those criteria include an individual displays symptoms of a learning disorder for more than six months, despite efforts to provide additional or specifically targeted instruction; the person's achievement in an academic domain (such as reading) is substantially below that expected given his or her age, schooling, and level of intelligence, and this learning disturbance interferes significantly with academic achievement or activities of daily living that require specific academic skills; the symptoms manifest during the individual's school-age years or young adulthood; and intellectual disorders, sensory problems, adverse learning conditions, and other potential causes have been ruled out. Earlier editions of the DSM listed four subcategories of learning disorders: reading disorder, mathematics disorder, disorder of written expression, and learning disorder not otherwise specified (NOS). However, the DSM-5 groups all learning disorders under the category of specific learning disorder. Specific learning disorder encompasses all varieties of learning disorders, including problems in reading, writing, and mathematics.

A variety of statistical approaches are used to produce an operational definition of academic achievement that is “substantially below” expected levels. Despite some controversy about its appropriateness, the most frequently used approach defines “substantially below” as a discrepancy between achievement and intelligence quotient (IQ) of more than two standard deviations (SD). In cases where an individual’s performance on an IQ test may have been compromised by an associated disorder in linguistic or information processing, an associated mental disorder, a general medical condition, or the individual’s ethnic or cultural background, a smaller discrepancy (between one and two SDs) may be acceptable. In general, the DSM-5 has moved somewhat away from the use of IQ tests in diagnosis, instead encouraging a greater focus on assessments that take environmental and other factors into account.

Differential diagnosis involves differentiating learning disorders from normal variations in academic achievement; scholastic difficulties due to lack of opportunity, poor teaching, or cultural factors; and learning difficulties associated with a sensory deficit. In cases of autism spectrum disorder, communication disorders, or mild intellectual disability, an additional diagnosis of learning disorder is given if the individual’s academic achievement is substantially below the expected level given the individual’s schooling and intelligence.

The term learning disorders was first applied to a clinical condition meeting these three criteria in the DSM-IV, published in 1994. Earlier editions of the DSM used other labels such as learning disturbance, a subcategory within special symptom reactions in DSM-II (1968). In DSM-III (1980) and DSM-III-R (1987), the condition was labeled academic skills disorders and listed under specific developmental disorders; furthermore, the diagnosis was based only on academic achievement substantially below the norm. The LD condition is also known by names other than those used in the psychiatric nomenclature, most frequently as learning disabilities, which may manifest in an imperfect ability to listen, think, speak, read, write, spell, or do mathematical calculations in children whose learning problems are not primarily the result of visual, hearing, or motor handicaps, mental retardation, emotional disturbance, or environmental, cultural, or economic disadvantage. Specific learning disorders are also commonly referred to by other names, such as dyslexia
(reading disorder), dyscalculia
(mathematics disorder), or dysgraphia (disorder of written expression). Empirical evidence about prevalence, etiology, course of the disorder, and intervention comes mainly from subjects identified as having dyslexia or learning disabilities.

Prevalence

Prevalence rates for learning disorders vary, depending on the definitions and methods of determining the achievement-intelligence discrepancy. According to a 2014 report by the National Center for Learning Disabilities (NCLD), approximately 5 percent of public school students in the United States have been diagnosed with a learning disorder; in addition, other children who fit the DSM-5's criteria may not yet have been officially diagnosed. The prevalence rate for specific subsets of specific learning disorder is more difficult to establish because many studies simply report the total number of learning disorders without separating them according to subcategory. According to the NCLD report, specific learning disorder with impairment in reading is the most common, followed by impairment in mathematics. Disorder of written expression alone is rare; it is usually associated with the other categories of specific learning disorder.

The NCLD report further states that male students are significantly more likely to be diagnosed with a learning disability than female students; as of 2014, two-thirds of diagnosed students were male. LD often coexists with another disorder, usually language disorders, communication disorders, or attention-deficit hyperactivity disorder (ADHD).

Etiology

There is strong empirical support for a genetic basis of reading disorders or dyslexia from behavior genetic studies. John C. DeFries and his colleagues indicate that heredity can account for as much as 60 percent of the variance in reading disorders or dyslexia. As for the exact mode of genetic transmission, Lon R. Cardon and his collaborators, in two behavior genetic studies, identified chromosome 6 as a possible quantitative trait locus for a predisposition to develop reading disorder. The possibility that transmission occurs through a subtle brain dysfunction rather than autosomal dominance has been explored by Bruce Pennington and others.

The neurophysiological basis of reading disorders has been explored in studies of central nervous dysfunction or faulty development of cerebral dominance. The hypothesized role of central nervous dysfunction has been difficult to verify despite observations that many children with learning disorders had a history of prenatal and perinatal complications, neurological soft signs, and electroencephalograph abnormalities. In 1925, neurologist Samuel T. Orton hypothesized that reading disorder or dyslexia results from failure to establish hemispheric dominance between the two halves of the brain. Research has yielded inconsistent support for Orton’s hypothesis and its reformulation, the progressive lateralization hypothesis. However, autopsy findings of cellular abnormalities in the left hemisphere of dyslexics that were confirmed in brain-imaging studies of live human subjects have reinvigorated researchers. These new directions are pursued in studies using sophisticated brain-imaging technology.

Genetic and neurophysiological factors do not directly cause problems in learning the academic skills. Rather, they affect development of neuropsychological, information-processing, linguistic, or communication abilities, producing difficulties or deficits that lead to learning problems. The most promising finding from research on process and ability deficits concerns phonological processing—the ability to use phonological information (the phonemes or speech sounds of one’s language)—in processing oral and written language. Two types of phonological processing, phonological awareness and phonological memory (encoding or retrieval), have been studied extensively. Based on correlational and experimental data, there is an emerging consensus that a deficit in phonological processing is the basis of reading disorder in a majority of cases.

Assessment

Assessment refers to the gathering of information to attain a goal. Assessment tools vary with the goal. If the goal is to establish the diagnosis, assessment involves the individualized administration of standardized tests of academic achievement and intelligence that have norms for the child’s age and, preferably, social class and ethnicity. To verify that the learning disturbance is interfering with a child’s academic achievement or social functioning, information is collected from parents and teachers through interviews and standardized measures such as rating scales. Behavioral observations of the child may be used to supplement parent-teacher reports. If there is a visual, hearing, or other sensory impairment, it must be determined that the learning deficit is in excess of that usually associated with it. The child’s developmental, medical, and educational histories and the family history are also obtained and used in establishing the differential diagnosis and clarifying etiology.

If LD is present, then the next goal is a detailed description of the learning disorder to guide treatment. Tools will depend on the specific type of learning disorder. For example, in the case of dyslexia, E. Wilcutt and Pennington suggest that the achievement test given to establish the achievement-intelligence discrepancy be supplemented by others such as the Gray Oral Reading Test, a timed measure of reading fluency as well as of reading comprehension. Still another assessment goal is to identify the neuropsychological, linguistic, emotional, and behavioral correlates of the learning disorder and any associated disorders. A variety of measures exist for this purpose. Instrument selection should be guided by the clinician’s hypotheses, based on what has been learned about the child and the disorder. Information about correlates and associated disorders is relevant to setting targets for intervention, understanding the etiology, and estimating the child’s potential response to intervention and prognosis.

In schools, identification of LD involves a multidisciplinary evaluation team, including the classroom teacher, a psychologist, and a special education teacher or specialist in the child’s academic skill deficit (such as reading). As needed, input may be sought from the child’s pediatrician, a speech therapist, an audiologist, a language specialist, or a psychiatrist. A thorough assessment should provide a good description of the child’s strengths as well as weaknesses that will be the basis of effective and comprehensive treatment plans for both the child and the family. In school settings, these are called, respectively, an Individualized Education Plan (IEP) and an Individual Family Service Plan (IFSP).

Treatment

Most children with LD require special education. Depending on the disorder’s severity, they may learn best in a one-to-one setting, small group, special class, or regular classroom plus resource room tutoring.

Treatment of LD should address both the disorder and associated conditions or correlates. Furthermore, it should include assisting the family and school in becoming more facilitative contexts for development of the child with LD. Using neuropsychological training, psychoeducational methods, behavioral or cognitive behavioral therapies, or cognitive instruction, singly or in combination, specific interventions have targeted the psychological process dysfunction or deficit assumed to underlie the specific learning disorder; a specific academic skill such as word attack; or an associated feature or correlate such as social skills. Process-oriented approaches that rose to prominence in the 1990s are linguistic models aimed at remediating deficits in phonological awareness and phonological memory and cognitive models that teach specific cognitive strategies that enable the child to become a more efficient learner. Overall, treatment or intervention studies during the last two decades of the twentieth century and at the beginning of the twenty-first century are more theory-driven, built on prior research, and rigorous in methodology. Many studies have shown significant gains in target behaviors. Transfer of training, however, remains elusive. Generalization of learned skills and strategies is still the major challenge for future treatment research, and LD remains a persistent or chronic disorder.

Bibliography

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