Chapter 32

32

Intellectual Disability

Fernhall and Baynard

C H A P T E R

Definition

• According to the American Association on Intellectual and Developmental Disabilities (AAIDD), an intellectual disability (ID) is characterized by significant limitations both in intellectual functioning and in adaptive behavior, which covers many everyday social and practical skills. This disability originates before the age of 18. The AAIDD definition has been adopted by the Social Security Administration.

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Definition (continued)

• The preceding definition differs slightly from the one in the Diagnostic and Statistical Manual of Mental Disorders-V (DSM-V), which requires deficits in two of three adaptive behaviors (AAIDD definition requires a deficit in only one of the adaptive behaviors). Adaptive behaviors include conceptual, social, and practical skills.

Scope

• Estimated prevalence in industrialized societies is ~3%; ~9 to 10 million individuals with ID in the United States

• >90% of all persons with ID are classified with mild ID

• Most individuals with ID live in the community, either at home or in community-based group homes

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Scope (continued)

• Individuals with more severe forms of ID live in community-based facilities that offer more specialized and intensive support.

• Mortality is estimated to be 1.5 to 4 times higher in people with ID than in the general population.

• Mortality is linked to the low IQ and poorer self-care skills of persons with ID.

Pathophysiology

• Several hundred causes of ID have been identified or suspected, but still, in half to one-third of individuals with ID the cause is unknown.

• The three major causes of ID are fetal alcohol syndrome, fragile X syndrome, and Down syndrome (DS).

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Pathophysiology (continued)

• Causes of ID usually fit into one of the following categories:

– Genetic (DS or trisomy 21 most common)

– Problems during pregnancy (most commonly due to maternal alcohol or drug use)

– Problems at birth

– Problems after birth

– Poverty and cultural deprivation(continued)

Table 32.1

Pathophysiology (continued)

• For individuals with DS, leukemia, infections, and the early development of Alzheimer’s disease are the most frequent causes of both mortality and morbidity; life expectancy is now often 60 yr.

– Primary risk factor for DS is maternal age, and 50% of those born with DS have associated congenital heart disorder.

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Pathophysiology (continued)

• For persons with ID not due to DS, cardiovascular and pulmonary disorders are the most common medical problems; life expectancy is approaching that of the general population.

• ID is associated with greater prevalence of obesity; among patients with DS, fitness is reduced as well, which may be tied to congenital heart disease.

Clinical Considerations

• Major signs and symptoms are usually related to delayed developmental stages in infants and children, including delays in sitting up, crawling, walking, or talking.

• Most developmental milestones are delayed, but the amount of delay depends on the severity and cause of the disability.

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Clinical Considerations (continued)

• Later in childhood, a child with ID may have difficulties understanding directions and experience problems with logical thinking, problem solving, or both.

• Children with ID may be unable to understand social rules or the consequences of their actions.

Physical Examination

• History and physical exam should follow standard formats.

• History needs to be acquired from a significant caregiver, as individuals with ID may not accurately remember their history.

• Individuals with DS: Obtain information on congenital heart disease and any joint problems, such as instability of the atlantoaxial joint in the upper neck (i.e., where the base of the skull meets the neck).

Testing for Diagnosis and Prognosis

• Chromosomal microarrays are used as a first-tier genetic test among individuals with unexplained IDs.57

• G-banded karyotyping should be reserved for individuals with obvious chromosomal problems and/or a family history of genetic abnormalities.57

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Testing for Diagnosis and Prognosis (continued)

• ID is diagnosed through the use of two types of tests: standardized tests of intelligence (IQ tests) and adaptive behavior (tests that address conceptual, social, and practical skills). The cutoff score used for both criteria is generally 2 standard deviations below the mean for the particular assessment instrument.

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Testing for Diagnosis and Prognosis (continued)

• Making the diagnosis of ID is important because it establishes eligibility for special education and home- or community-based services; social security benefits; and special treatment within the criminal justice system. Individuals with ID may also require additional testing for hypothyroidism, congenital heart disease, atlantoaxial instability, hearing, and vision.

Exercise Testing

• Although research data are limited, testing is largely safe.

• Be aware of a possibly diminished ability to understand and follow instructions and cooperate with the testing procedures.

• Pretest screening should be consistent with ACSM guidelines. Note that nearly half of all individuals with DS have congenital heart disease.

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Exercise Testing (continued)

• Consider a familiarization test before real test; incorporate detailed, step-by-step instructions.

• Use a population-specific formula to estimate maximum heart rate: 210 – 0.56(age) – 15.5(DS). DS = 1 for non-DS and 2 for DS.

Treatment

• No treatment per se• Individualize support specific to each

individual, outlining detailed strategies and services over a sustained time period

• Increased physical activity, formal exercise programming, or both are important aspects of maintaining health in persons with ID.

• Many individuals with ID are treated for symptoms of depression with antidepressive medications, and many individuals with DS are treated for thyroid disorders as well.

Exercise Prescription

• Exercise prescription for individuals with ID is quite similar to that for nondisabled adults.

• Incorporate much positive encouragement.

• Close supervision is likely needed in the beginning when starting a nonexerciser on an exercise program.

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Exercise Prescription (continued)

• Individualized exercise appears to be more effective than group format.

• Incorporate simple games and music into an exercise training program, or use participation in activities akin to the Special Olympics, for increased motivation.

• Exercises that may involve hyperflexion or hyperextension of the neck are contraindicated due to a high rate of atlantoaxial instability.

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Exercise Prescription (continued)

• Individuals with DS often present with skeletal muscle hypotonia and joint laxity. To avoid hyperextension or hyperflexion, ensure that the individual is performing the exercise in a smooth and controlled manner and is not “jerking” through a given exercise with excessive momentum.

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Exercise Prescription (continued)

• Pulmonary hypoplasia may also be present in individuals with DS. Possible modifications may be needed to the exercise prescription (i.e., intensity) depending on the severity of the hypoplasia, especially if exercise is performed at altitude.

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Exercise Prescription (continued)

• Specific physical features may limit exercise performance, such as short stature and short limbs and digits. These characteristics may be coupled with additional characteristics such as malformed feet and toes, a small mouth or small nasal cavities, and a large or protruding tongue. Poor vision and balance may also contribute to reduced exercise performance.

Conclusion

• ID is not a disease, and there is no cure.

• Just like people with chronic diseases or other disabilities, individuals with an ID can both participate in and enjoy the benefits derived from a regular exercise program.

• This is a distinctive and special population of individuals who are well deserving of the skills and abilities of the practicing clinical exercise physiologist.