The field of developmental disorders has experienced multiple scientific and social changes in the last decade. Many changes involve the perception of disabilities and have been referred to by Dennis Harper as a shift in paradigms. Some of these changes in the definition of developmental and learning disorders have resulted in changes in societal responses to children and adults with disabilities. In addition, advances in neuropsychological research, imaging, and genetics have refined researchers’ understanding of developmental and learning disorders.
Definition of Developmental Disorders
The implications of developmental disorder classification and resultant diagnostic labels have a major impact on diagnostic systems, scientific study of developmental disorders, and service-based educational intervention and treatment programs for children and youth. The largest impact on children and youth is related to how such definitions become incorporated into administrative rules for the delivery of special education services in schools and related supports in community-based rehabilitation and treatment settings.
Early definitions of developmental disability are relevant to the understanding of the current status of developmental disorders. The earliest definitions of developmental disabilities were crafted in Public Law 91-517 in 1970. This law was an outgrowth of the work of several forward-thinking individuals who assisted on the president’s panel on mental retardation at the request of President John F. Kennedy in 1961. This effort was directed toward prevention in mental retardation worldwide. This panel and its outcomes set the stage for subsequent legislation related to developmental disabilities and later, developmental disorders. This presidential panel made important contributions that expanded early definitions and approaches to the treatment of developmental disabilities. These contributions included keeping children with disabilities in their normal or local environments; supporting those with physical impairments; encouraging a blended continuum of medical, educational, and social care throughout the life span; recognizing a coordinated, interdisciplinary treatment approach; focusing intervention on local and state levels; and encouraging coordination between university medical professionals and state provider agencies. This panel laid the structure for many important aspects of defining and treating developmental disorders in the next several decades.
Over the next three decades (1970-2000), the definition of developmental disabilities changed in scope and complexity. Most important, in 1975, Public Law 94-103 broadened the developmental disabilities definition to include autism and a few specific learning disabilities (e.g., dyslexia) if those learning disabilities related to existing and concurrent developmental disorders. The Developmental Disabilities Act (Public Law 95-605) of 1978 was a detailed explanation that set federal policy and state educational treatment for developmental disorders for many years to come. Newer definitions became less categorical and emphasized functional limitations. Use of the term impairment was also advocated and reference to disease was often removed.
Contemporary Issues in Defining Developmental Disorders
Contemporary research and practice for developmental disorders evolved with a more specific focus on components of learning difficulties, or subtypes of learning difficulties. Researchers primarily in the United States separated learning disorders from mental retardation and identified the components of learning disorders in children and adults. Attention focused on memory factors, attentional characteristics, and visual-spatial skills of the learner. In addition, there has been a move toward functional perspectives with particular developmental disorders or disabilities. This approach focuses on more discrete description of skills and adaptive behaviors that individuals need to perform in daily situations. In the past, often the relationship between specific medical diagnostic etiologies and learning disorders did not appear to capture what most individuals needed with respect to their instructional assistance and functioning.
The current definitional trend in developmental disorders also reflects the importance of support-based paradigms in specifying treatments and services for developmental disorders, as noted by Ruth Luckasson and colleagues. These movements, largely focusing on individuals with mental retardation, do affect the diagnosis and treatment of developmental disorders. Proponents of this support-based orientation of defining disabilities emphasize the opportunity for greater flexibility in diagnosing and classifying such disorders. This shift in thinking is not without controversy. The seemingly simple idea of providing a general diagnosis based upon functional differences related to available supports raises many questions about service provisions, inclusion in instruction, and who has a developmental disorder.
An equally complicating task in defining developmental disorders is related to comorbidity of the developmental problem. In its simplest terms, comorbidity is the condition when two different “disease processes” are present in the same individual. It is relatively common for learning disorders to be associated with attention difficulties, either as a primary diagnosis or as a secondary and concurrent problem. This comorbidity extends to all other emotional and behavioral disorders, and its co-occurrence clearly complicates the diagnostic evaluation procedure and treatment recommendations and potential remediation of the developmental disorder. Progress in the remediation of developmental disorders may often be related to its coexistence with other disorders.
It is also important to ascertain which disorder, if either, is primary. This has implications for all aspects of treatment and types of remediation. Steven Pliszka, Caryn Carlson, and James Swanson have noted multiple diagnostic treatment issues for attention deficit hyperactivity disorder (ADHD) with comorbid learning disorders. They describe “an overlap between LD and ADHD” for varying learning disorders (reading, spelling, and arithmetic). Furthermore, they report average percentages of 20% to 30% for co-occurrence of ADHD with learning disorders (LD). More generally, learning disorders coexist with other psychiatric disorders. It has been estimated that 10% to 25% of people (children and adults) with LD as defined in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) have coexisting disorders such as conduct disorder, oppositional defiant disorder, ADHD, and depressive disorders. Such comorbidity clearly can complicate the diagnosis and treatment of any developmental disorder.
Defining and “diagnosing” a learning disability has reflected and continues to reflect multiple viewpoints, and this is emphasized in the recently defined Individuals with Disabilities Education Act (IDEA) legislation (Public Law No. 105-17). This information, which appears in the Federal Register for 1997, delineates a definition of “specific learning disability” and outlines criteria for learning disabilities. This is an important definition and details many issues in the definition of learning disability. It indicates that a learning disability must result from a deficit in one or more basic learning areas such as memory, reasoning, organization, and perception; must manifest itself in the form of one or more significant learning difficulties in one or more of seven areas—oral expression, listening comprehension, written expression, basic reading skills, reading comprehension, mathematic calculations, and mathematical reasoning—compared with other children of the same age; must be evidenced by a significant discrepancy between intellectual ability and academic achievement in at least one of these cited seven areas; and must not be caused by mental retardation, hearing or vision impairment, motor impairment, emotional or behavioral disorder, or environmental disadvantage. This is a very general description of learning disabilities, and it encompasses a large number of possible characteristics. It consists of multiple characteristics for inclusion as well as exclusion.
Another contemporary method of defining a learning disability appears in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR). The DSM—IV—TR defines three major types of learning disorders—reading disorder, mathematics disorder, and disorder of written expression—and also a learning disorder not otherwise specified (NOS). No general definitions of learning disability are offered. Also a discrepancy must appear between achievements in the areas of deficit and an individual’s measured intelligence. This ability/achievement discrepancy is probably the most contentious issue in the area of defining learning disabilities at this time.
There are multiple concerns in using the ability/ achievement discrepancy as a key factor in defining learning disorders or learning disorder subtypes. Several authors (e.g., Keith Stanovich & Jack Fletcher, David Francis, Byron Rourke, Sally Shaywitz, and Benny Shaywitz) have noted that such discrepancy models do not differentiate subtypes of learning disorders, fail to consider the complex etiologies of learning disorders, obscure differences associated with the identification of gifted children, and may overidentify more intelligent children as learning disabled. Using the ability/achievement discrepancy as a key proxy for learning disorders appears to be an oversimplification of the complex processes involved in defining and understanding learning disorders.
Contemporary approaches to defining learning disabilities have focused on a neuropsychological assessment. John Obrzut and George Hynd present an especially balanced view of the relevance of neuropsychological data to learning disabilities. A few key points are worth noting. First, general ability testing does not provide much guidance in the specifics of remediation for learning disorders. The hallmark of neuropsychological evaluation is identifying the relationship between certain “brain-related” functions and central nervous system (CNS) locations and func-tional behavior. Neuropsychological tests provide data concerning perception, attention, memory, motor skill, language, and reasoning. At its best, such assessment relates status factors to actual function. Neuropsychological assessment independently seldom contributes to the amelioration of learning disorders. It can provide documentation of acquired deficits as they relate to learning performance. Rather significantly it is the neuropsychologist’s knowledge of brain and behavior relationships that provides useful information, not the tests or their outcomes per se. Although obvious, this mundane point is central to the diagnostic process in understanding the diagnosis and remediation of learning disorders and information provided by competent neuropsychologists.
Causes of Developmental Disorders
Hypotheses regarding the causes of learning disorders are well outlined by the team of Daniel Hallahan, James Kauffman, and John Lloyd and by Obrzut and Hynd. There is evidence for neurological differences in the brains of those with dyslexia based upon magnetic resonance imaging (MRI) and positron emission tomography (PET) studies. Evidence suggests functional and structural differences in the CNS of those with reading disorders. Family studies by Christopher Chase, Glenn Rose, and Gordon Sherman have implicated heredity in dyslexia. However, the specifics of genetic transmission are yet to be clarified for dyslexia or specific learning disorders. Teratogens such as alcohol, cigarettes, and illegal drugs have been associated with possible learning disabilities. Perinatal influence such as prematurity and postnatal events such as head injury, lead poisoning, and malnutrition have all been implicated but only in a general sense. The human genome studies will undoubtedly provide some specifics in the next few years.
Subtypes of Developmental Disorders
For purposes of clarity and specificity, this entry focuses on learning disorders as classified in the DSM—IV—TR (2000).
Learning disorders are diagnosed when the individual’s achievement on individually administered, standardized tests in reading, mathematics, or written expression is substantially below that expected for age, schooling, and level of intelligence. Assessment of this last item—level of intelligence—is a requirement for diagnosis of all developmental disorders listed in DSM—IV—TR. The learning problems significantly interfere with academic achievements or activities of daily living that require reading, mathematics, or writing skills. A variety of statistical approaches may be used to establish that a discrepancy is significant. “Substantially below” usually refers to a discrepancy of more than 2 standard deviations between achievement and measured IQ. A smaller discrepancy between achievement and IQ is also used, especially in cases when an individual’s performance on an IQ test may have been compromised by an associated disorder in cognitive processing, a comorbid mental disorder, a general medical condition, or the individual’s ethnic or cultural background. If a sensory deficit is present, the learning difficulties must be in excess of those usually associated with the deficit.
Deciding what is a significant deficit is not easily accomplished. It is unclear what should be considered the “measured IQ point,” the total score, or particular subsets, all of which are affected by the underlying learning disorder. This is true for all subtypes. Learning disorders persist into and through adulthood; however, they change in their presentation as functions of time and experience. Residual aspects are difficult to clarify in long-standing learning disabilities especially when impacted by motivational aspects. It is generally estimated that the prevalence of learning disorders ranges from 2% to 10%, depending on the nature of ascertainment and the definitions applied. Reportedly, 5% of students in public schools in the United States are identified as having a learning disorder.
Reading disorders are characterized by reading achievement substantially below that expected for age, intelligence, and educational level and that significantly interferes with academic achievement or activities of daily living and in excess of any reading difficulties due to otherwise present sensory deficits. Reading disorder, often called dyslexia, is characterized by oral reading distortions, substitutions, omissions, slow reading, and limited comprehension. Symptoms of reading disorder may occur as early as kindergarten, but it is rarely diagnosed before the beginning of first grade when formal reading instruction begins. In children with high IQ, it may not be diagnosed until after fourth grade, because they may continue to function at or near grade level. A reading disorder follows familial trends, being more prevalent among first-degree relatives of individuals with learning disorders, and it is more prevalent among males. The prevalence of reading disorder in the United States is estimated at 4% of school-age children.
The criteria for mathematics disorder include having mathematical ability substantially below that expected for a person’s age, intelligence, and education. This learning disorder must interfere with academic achievement or activities of daily living and supersede mathematical difficulties associated with other present sensory deficits. Such mathematics disorders are estimated to be present in approximately one in every five cases of learning disorder, affecting approximately 1%of school-age children. Multiple skills are impaired in mathematics disorder: linguistic skills—understanding and naming math operations, concepts and decoding written problems, perceptual skills—recognizing numerical signs and symbols, and attentional skills—copying numbers, recalling and completing arithmetic functions, following sequences, and multiple step operations. This disorder reflects a complicated set of deficits in learning skills applied to mathematical concepts and computations. Characteristics of a mathematics disorder may appear as early as kindergarten; however, it is rarely diagnosed before formal mathematics instruction occurs, usually at the end of first grade. If mathematics disorder affects children with high intelligence, they may continue to function at or near grade level in early grades, resulting in the disorder not becoming apparent until they are in the higher grades.
Disorder of Written Expression
Disorders of written expression are characterized by writing skills substantially below those expected for an individual’s age, intelligence, and education. This learning disorder must interfere with academic achievement or activities of daily writing, and if sensory deficits are present, the difficulties must be in excess of those associated with the current sensory deficit. The difficulties in writing skills are generally apparent in a combination of grammatical or punctuation errors, poor paragraph organization, multiple spelling errors, and excessively poor handwriting, although poor handwriting and spelling errors alone are not necessarily indicative of a disorder of written expression. Poor handwriting and spelling, also called “poor graphomotor skills,” is often overdiagnosed as the primary problem. A disorder of written expression rarely occurs separate from other learning disorders, and its exact prevalence is unclear. Characteristics of the disorder of writing expression may appear in first grade, but it is usually more apparent in second grade or after formal writing instruction has occurred. Currently less is known about this disorder.
Learning Disorders Not Otherwise Specified
This category is for learning disorders that do not “meet criteria” in DSM-IV-TR for any particular disorder. When all three features of the subtypes co-occur, this category is used. When the data are equivocal, this is the diagnosis. In some instances, those with other less defined learning disabilities (nonverbal LD) are given this diagnosis.
It is quite clear that the subtype definitions of learning disorders as appearing in DSM-IV-TR are not easy to diagnose and are affected by the ability/achievement discrepancy model definition. These subtypes should be used as guidelines for understanding the possible learning disorders and need to be combined with other behavioral, achievement, and assessment characteristics. The criteria as outlined for each disorder in
DSM-IV-TR are again guidelines for initial inclusion of these diagnostic categories.
Other Learning Disability Subtypes
Nonverbal learning disorders (NLD; often referred to as right-hemisphere learning disorders) have been identified for some time and are well outlined by Rourke. Currently, the “NLD syndrome” is quite broad and has a variety of characteristics associated with it. According to Sue Thompson, the NLD syndrome reveals itself in impaired abilities to organize the visual-spatial field, adapt to new or novel situations, or accurately read nonverbal signs and cues. Individuals have difficulties in situations requiring speed and adaptability. Nonverbal learning disabilities reportedly involve performance processes often thought of neurologically as originating in the right hemisphere. Much of the initial discovery of NLD syndrome reportedly began in the early 1970s with research involving groups of children with learning disabilities identified by discrepancies between their verbal and performance intelligence abilities. Again such discrepancies are noteworthy but are only a starting point for the diagnostic process.
Thompson lists the following common characteristics of nonverbal learning disorders: “performance IQ significantly lower than verbal IQ, early speech and vocabulary development delayed, remarkable rote memory skills, attention to detail, early reading skills, excellent spelling skills, expresses himself eloquently, lack of coordination, severe balance problems and difficulties with fine motor skills, lack of image and poor visual recall, faulty spatial perceptions, difficulty with spatial relations, lack of ability to comprehend nonverbal communication, difficulties adjusting to transitions and new situations, and significant deficits in social judgment and interaction” (p. 15).
A clear designation of these characteristics is difficult given the current state of research and the wide array of characteristics often reportedly associated with NLD Syndrome. It should, however, be acknowledged that such problems do exist and need to be understood within the context of developmental disorders.
Developmental disorders are neither easily diagnosed nor easily remediated with existing instructional techniques. All definitions are guidelines—helpful, but rarely definitive in their application or discrimination. Assessment and remediation of learning disorders is best accomplished by several individuals. Evaluations completed by a competent neuropsychologist and an educator who are both familiar with developmental processes, measurement methods, CNS functioning, and specific remediation techniques are mandatory. In some instances, the learner’s neurological status may require review by a medical professional. Rarely is vision the key reason for a LD. With adults, one is often dealing with comorbid disorders and some longstanding failure and its resultant impact on the learner’s self-esteem.
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