1. Intellectual or Cognitive Disabilities

2. Developmental Disabilities

3. Global Developmental Delay

Intellectual or Cognitive Disabilities

A cognitive or intellectual disability is characterized by significantly lower average scores on standardized tests of mental ability or intelligence and by lower academic functioning and limitations in the ability to function in areas of daily life.

There are different degrees of Intellectual disability, ranging from low average to mild, moderate, and profound. A person's level of Intellectual disability can be defined by their intelligence quotient (IQ), as measured with IQ Tests.

NB.: The dividing line between categories is given as a range because IQ scores may involve a measurement error of approximately 5 points.

Low Average Learner

A Low Average Learner is a person whose intellectual functioning is within the Low Average range when compared with age-peers. It is marked by IQ scores ranges from 80-89.  A low Average Intellectual Disability is accompanied by concurrent deficits in academic achievement and/or impairment in adaptive functioning.

Borderline Intellectual Disability

This descriptive label is used when the focus of clinical attention is associated with borderline intellectual functioning; that is, an IQ in the 71-84 range.  A Below Average Intellectual Disability presents failure to develop adaptive behavior and academic performance appropriate with age-peers. 

Mild Intellectual Disability

A Mild Intellectual Disability is characterized by IQ score ranges from 50–70 and deficits in two or more areas of adaptive behavior or daily functioning. Affected skills could include the ability to understand language (communication), home  skills, use of community resources, health, safety, leisure, and social skills, self-direction, functional academic skills (reading, writing, and arithmetic), and work skills.

Moderate Intellectual Disability

A Moderate Intellectual Disability entails IQ scores ranging from 35–55.  Individuals with Moderate Intellectual Disability also have deficits in several areas of adaptive behavior or daily functioning.  Concurrent deficits in academic and adaptive functioning are congruent with the moderate Intellectual disability. 

Severe Intellectual Disability

A Severe Intellectual Disability applies to persons with IQ scores of 20–40. Persons with Severe Intellectual Disability have deficits in most areas of adaptive behavior or daily functioning.  The academic and adaptive functioning is commensurate with the extent of the intellectual disability.

Profound Intellectual Disability

Individuals with Profound Intellectual Disability have IQ scores under 20–25. Their intellectual disability is often caused by an accompanying neurological disorder, which correlates with the extent of the intellectual disability, and academic, and adaptive skills.

The American Association on Mental Retardation (AAMR) has developed another concomitant diagnostic classification system for intellectual disabilities. The AAMR classification system refers to the "below-average intellectual function" as an IQ of 70–75 or below.  The AAMR classification system focuses on the capabilities of the intellectually disabled individual rather than on his or her limitations. The categories describe the level of support required. They are: intermittent support; limited support; extensive support, and pervasive support.  To some extent, the AAMR classification mirrors the DSM-IV-TR classification. Intermittent support, for example, is support that is needed only occasionally, perhaps during times of stress or crisis for the intellectually disabled person. It is the type of support typically required for individuals with a mild intellectual disability. At the other end of the spectrum, pervasive support, or life-long, daily support for most adaptive areas, would be required for individuals with profound intellectual disability.

Etiology

A wide variety of medical and environmental conditions can cause Intellectual Disabilities. Some are genetic, and some are present before, during or after birth.  These abnormalities may be physical as well as neurological and may include unusual features, deformities of the hands and feet, and other abnormalities. Causes for cognitive disabilities are many, and include:

Genetics: Down Syndrome, Fragile X Syndrome; Phenylketonuria (PKU), Trisomy 18. 

Prenatal: Fetal Alcohol; HIV; Birth trauma or hypoxia; use of harmful drugs. 

Perinatal: Cerebral ischemia; Maternal deprivation; Hypothyroidism; Prematurity.

Maternal infections: Rubella; Cytomegalovirus Infection; Hypertension; Blood Poisoning (Toxemia).  

Childhood: Meningitis and encephalitis; Head trauma; Lead poisoning; Whooping cough; Chickenpox, Measles. 

Environmental factors: Maternal malnutrition; Unhealthy living conditions; Inadequate medical care.

Diagnosing Intellectual Impairment

Children are administered intelligence tests to measure their cognitive functioning, academic achievement, and adaptive skills. Intellectual tests include the Stanford-Binet Intelligence Scale, the Wechsler Intelligence Scales, and the Wechsler Preschool and Primary Scale of Intelligence. For infants, the Bayley Scales of Infant Development may be used to assess motor, language, and problem-solving skills. In adults, the Wechsler Adult Intelligence Scale (WAIS-III) is used. 

Academic achievement can be assessed with such tests as the Wechsler Individual Achievement Test (WIAT-III), the Kaufman Test of Educational Achievement (KTEA-II), and the Woodcock-Johnson.   For children under the age of 6 the following achievement tests can be used: the Kaufman Survey of Early Academic and Language Skills (K-SEALS); the Kindergarten Readiness Test (KRT), and the Metropolitan Readiness Test-Sixth Edition (MRT-6). 

Adaptive skills are measured with such tests as the Adaptive Behavior Assessment System (ABAS). The ABAS assesses 10 skill areas: communication, community use, functional academics, school living, health and safety, leisure, self-care, self-direction, social, and work. 

Also, the Woodcock-Johnson Scales of Independent Behavior and the Vineland Adaptive Behavior Scale (VABS) are frequently used to test these skills.  

Prevention

Immunization against diseases such as measles and Hib disease (a bacterial infection) prevents many of the illnesses that can cause intellectual impairment. In addition, all children should undergo routine developmental screening as part of their pediatric care. Screening is particularly critical for those children who may be neglected or undernourished or may live in disease-producing conditions. Newborn screening and immediate treatment for PKU and hyperthyroidism can usually catch these disorders early enough to prevent retardation.  Good prenatal care can also help prevent cognitive impairment. Pregnant women should be educated about the risks of drinking and the need to maintain good nutrition during pregnancy. Tests such as amniocentesis and ultrasonography can determine whether a fetus is developing normally in the womb.

Interventions

All children with intellectual disabilities benefit from special education. The federal Individuals with Disabilities Education Act (IDEA) requires public schools to provide free and appropriate education to children and adolescents with intellectual disabilities or other developmental disorders. Education must be provided in the least restrictive, most inclusive setting possible–where the children have every opportunity to interact with non-disabled peers and have equal access to community resources.

Resources

American Association on Mental Retardation (AAMR). 444 North Capitol St., NW, Suite 846, Washington, D.C. 20001-1512. (800) 424-3688. http://www.aamr.org.

The Arc. 900 Varnum Street NE, Washington, D.C. 20017. (202) 636-2950. http://www.thearc.org.

Learning Disabilities Association of Ontario (LDAO) http://www.ldao.ca

Developmental Disability

A developmental disability is a term used to describe life-long disabilities attributable to  intellectual and physical impairments, manifested prior to age 18.  The intellectual impairment is accompanied with physical impairments and/or birth defects that affect the functioning of the brain, spinal cord, and nervous system, and which can impact on learning.  In most cases,  functioning includes language, visual-spatial skills and/or motor coordination impairments. 

Developmental disabilities include genetic (Down syndrome) and metabolic disorders (Phenylketonuria: PKU and Hypothyroidism), degenerative disorders (Rett syndrome), and sensory-related disabilities (e.g., congenital rubella and William syndrome). 

Global Developmental Delay

The essential feature of Global Developmental Delay is delay in achieving milestones within most, if not all, of the developmental domains. The term is only used for very young children. The etiology in most cases in unknown and there is continuing uncertainty as to the causes of the delay.

These  domains of development can be summarized as follows:

·       motor skills (milestones in this domain include, gross motor skills such as sitting up or rolling over and fine motor skills such as picking up small objects)

·       speech and language (which also includes babbling, imitating speech, identifying sounds, communicating using non-verbal means such as gesture, facial expression, eye contact and posture, and understanding what others are trying to communicate to you – comprehension or “receptive language”)

·       cognitive skills (the ability to learn new things, filter and process information, remember and recall, and to reason)

·       social and emotional skills (interacting with others and development of personal traits and feelings).

Intervention

Children develop at different rates and the age at which a particular child reaches a specific developmental milestone can vary substantially. In fact, some children who do not reach developmental milestones on time may catch up later, sometimes with and sometimes without extra support, have no permanent problems and go on to develop normally. Nonetheless, it is important for the child to be seen by a professional, as it is often the case that children will go on to develop normally when given support: e.g., Speech and Language Therapy, Occupational Therapy and/or Physiotherapy.

Differential Diagnosis

Global developmental delay is to be differentiated from learning disabilities disabilities. For instance, significant language delay is often accompanied by difficulties in reading and spelling, and dysfunction in interpersonal relationships and emotional behavioral disorders. 

Also, global developmental delay should be differentiated from cognitive or intellectual disabilities. Because intelligence includes verbal skills, it is likely that a child, whose intellectual disability is significantly below average, will also show language development that is below average.  Accordingly, when a language delay is accompanied by an intellectual disability, the diagnosis of intellectual disability would be appropriate.

If the global developmental delay is secondary to a physical disability (e.g., severe deafness or some specific neurological or structured dysfunction of development), there is likely to be marked delay in language development, and hence the language delay is a direct consequence of a hearing impairment or other sensory condition (e.g., blindness and poor vision or hearing impairments).

Global developmental delay should be differentiated from expressive language disorder, receptive language disorder, mixed expressive-receptive language disorder, developmental coordination disorder, and acquired aphasia with epilepsy (Landau-Kleffer syndrome).

References

American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4^th ed). Washington, DC: Author. 

World Health Organization. (1992). The ICD-10 classification of mental and behavioral disorders. Geneva: Switzerland.