Intellectual Disabilities

By Jennifer Oden, Loyola Marymount Los Angeles, Masters in School Psychology
Boy potentially with intellectual disabilities.

Learning to understand and be at be with intellectual disabilities.

Recently, the term Intellectual Disabilities was created as a new descriptive term that refers to the same population of individuals who were diagnosed previously with Mental Retardation.  Individuals with intellectual disabilities are the same as individuals with mental retardation in number, kind, level, type, and duration of disability. These are individuals who require individualized services and supports.

All individuals who were eligible for a diagnosis of Mental Retardation are now eligible for a diagnosis of Intellectual Disability, but many have yet to acquire the term Intellectual Disability – although it is presently preferred. It will take time for the term Intellectual Disability to be used in legislation and regulation, and for the names of organizations to change; however for the purposes of this article – Intellectual Disabilities or ID will be used.

    Development of the Field

    Research on Intellectual Disabilities (ID) started before most other disabilities. Physician Langdon Down was the first to create a classification system for individuals with ID in the 19th century. He was the first to describe the characteristics of children now referred to as having Down Syndrome. In the late 19th century, small residential facilities educated these individuals so that they could return to communities as more skilled adults. Special education classes started in public schools around same time. Overall, optimism began to prevail in terms of educating children with intellectual disabilities.

    Shifting Perspectives

    By the beginning of the 20th century, there was a radical shift in thinking about ID. Unfortunately, pessimism replaced optimism. Theories suggested that ID was inherited and accompanied by criminal tendencies. It was believed that allowing individuals with ID to reproduce would undermine the strength of American society. The United States started to abandon efforts to educate children with ID.

    Children with more severe cases of ID were kept at home or sent to residential institutions and kept from society. Children with mild cases of ID were confined to special classes and were not allowed to interfere with the educational progress of general education students. The early 20th century was the lowest point in modern history for those with ID.

    By the middle of the 20th century, things started changing. New research began challenging that all ID was inherited. Statistics were showing that children with ID were not predisposed to criminal activities. Studies began showing that those with mild ID performed better academically when they were integrated with the general education population. Parent organizations formed and began advocating for ID rights. Finally, the deplorable conditions of the residential institutions were exposed.

    In the 1960’s and 1970’s there was an emphasis on earning political rights for children with disabilities. Federal special education law (now referred to as the Individuals with Disabilities Education Act – IDEA) was formed.

      Previous Definitions: Mental Retardation

      Mental Retardation was the term used by IDEA, and was used by most states. Children with MR displayed:

      • Significantly sub-average general intellectual functioning, which exists concurrently with deficits in adaptive behavior and which manifested during the developmental period of life, and that adversely affects a child’s educational performance.
      • Low cognitive ability and low adaptive behavioral skills
      • Symptoms present prior to age 18 (for example: if an adult becomes injured and has significant cognition loss, the term cognitive impairment, NOT Mental Retardation would be used).

      American Association of Mental Retardation

      In 1992 the definition of MR was revised, but not yet changed in IDEA definition. Children with MR were classified as having:

      • Limitations both in intellectual functioning & in adaptive behavior as expressed in conceptual, social & practical adaptive skills.
      • Origins of the disability before age 18

      Five Essential Assumptions of Intellectual Disabilities

      1) Limitations in present functioning must be considered within context of community environment typical of individual’s age, peers, and culture.

      2) Valid assessments should consider cultural and linguistic diversity as well as differences in communication, sensory, motor & behavioral factors.

      3) Limitations coexist with strengths.

      4) A profile of necessary supports for the child should be determined (this is the reason for describing the child’s limitations).

      5) With applied individualized supports over a sustained period of time, functioning levels will generally improve.

        Prevalence of Intellectual Disabilities

        • Individuals with intellectual disabilities make up approximately 1% of the population (ages 6 to 21; and an additional .04% when considering developmentally delayed children ages 3 to 9)
        • In the 1970’s and 1980’s the prevalence of ID dropped significantly (partly due to better diagnosing & differentiation with other disabilities), but prevalence has remained stable for past several decades (partly due to stigma & avoidance of using the diagnosis)
        • Data suggests that school-age children with ID are under-identified
        • Slightly higher rate for boys (1.5 : 1)
        • Syndromes associated with ID affect boys & girls at different rates

        Causes of Intellectual Disabilities

        • In most cases, especially in cases of children with mild intellectual disabilities, the cause is unknown.
        • Mild ID with unknown causes was sometimes called “cultural familial retardation”  (early 20th century thinking that ID occurred in certain family groups and that acquiring intellectual disabilities was related to ways in which they lived).
        • In cases of more significant intellectual disabilities, the cause is often considered in terms of when symptoms occurred:
          • during prenatal (before birth):
          • perinatal (during or immediately after birth)
          • postnatal (after birth)
          • genetic & brain damage: (more severe intellectual disabilities causes)

        Genetic factors

        • Damage to genetic material (e.g., chromosomal abnormalities - Downs Syndrome)
        • Heredity transmission (inherited - e.g., Fragile X, PKU, and Tay-Sachs)

        Types of Intellectual Disabilities

        Down syndrome - most well known of genetic disorder resulting in intellectual disabilities.

        • 1 of 800/1000 kids born w/DS
        • cause is clear: (we all have 46 chromosomes; 23 from each parent) –extra chromosome on in the 21st pair (Trisomy 21)
        • when young: often poor muscle control (“floppy” babies);
        • eyes slant upward; small ears; large tongues
        • 1/2 have Vision or Hearing impairments
        • 1/2 have heart defects that may require medication or surgery
        • usually have mild to moderate intellectual disabilities
        • range of distinctive physical characteristics (vary among individuals)
        • small stature
        • speckling of the iris
        • small oral cavity (causing protruding tongue)
        • short & broad hands
        • wide gap between 1st and 2nd toes
        • shorter life expectancy due to medical conditions
        • There is a correlation with age of mother: mothers 25 yrs of age had a 1 in 1,350 of having a child with Downs Syndrome; however a mother 45 yrs old had a 1 in 28 chance of have child with Downs Syndrome.

        Fragile X syndrome: (AKA: Martin-Bell syndrome): most common form of inherited ID; both males and females carry the disorder, but only mothers transmit the disorder to their children.  It develops when a mutation occurs in one of genes in the X chromosome; the mutation (when a gene segment that is repeated in most people about 30 times is repeated 55 to 200times) causes the gene to turn off; that is, to stop producing a chemical. This results in the bottom of the X chromosome getting pinched off in some of the blood cells.

        • males: 1: 1200; females: 1: 2500  - occurs less often in females because they have an extra X chromosome
        • males often show more significant levels of ID; whereas females often show milder impairments
        • often long faces, large ears & poor muscle tone, but generally healthy
        • often show characteristics similar to ADHD (distractibility)
        • some characteristics of autism (hypersensitivity to certain stimuli & tendency to say or do same thing over & over again; anxious when routines change; poor social skills)

        Prader-Willi Syndrome:  much less common than Downs Syndrome & Fragile X

        • affects 1: 14,000 children
        • caused by any of several types of mutations on chromosome 15
        • mild or moderate ID, some have average to low average cognitive abilities.
        • often happy as toddlers with similar behaviors to peers
        • once they reach school age, significant behavior problems emerge (stubbornness, difficulty switching activities, resistance to change in routines)
        • PRIMARY characteristics: insatiable appetite & compulsive eating (usually starting between ages 2 to 4 yrs old). May steal food, eat discarded food, have to lock food away; obesity in 95% if food intake isn’t controlled.
        • need constant control & extensive behavioral intervention

        Fetal Alcohol Syndrome (FAS)

        • 1973 – term was first used
        • significantly underreported: 0.33 to 2.2 cases per 1000
        • some proposed 2/3 of all special education children are affected by FAS or FAE (effects)
        • leading cause of ID
        • only cause that is preventable!
        • children are smaller & slower in development
        • small eyes with drooping eyelids; groove between lip & nose absent
        • lower part of face is flat
        • often mild or moderate ID
        • also likely: short attention spans, hyperactivity, learning disabilities, and poor coordination.

        PKU (Phenylketonuria) is an inherited metabolic disorder that results in ID if untreated.

        • affects 1 out of 15,000 babies;
        • children are unable to produce chemicals needed to convert other toxic chemicals into harmless products; accumulation of PKU results in abnormal brain development
        • both parents have to carry the defective gene to pass it on
        • affects boys and girls equally
        • all states mandate testing of newborns for PKU
        • treatment begins immediately: carefully planned diet throughout life
        • if diet followed & chemical levels monitored = no sig effects

        Tay-Sachs Disease

        • appears when both mother & father are carriers
        • progressive brain damage & eventual death


        • parasitic infection
        • 10-15% of childbearing age women
        • usually harmless because immune system prevents illness; but pregnant woman can pass to newborn. Babies might seem fine, but ID or blindness may develop
        • parasite: spread through cat fecal matter & infected meat

        Perinatal causes of ID:

        • premature birth weight: babies weighing less than 3.3 lbs will have a 10-15% risk of ID
        • birth injuries: deprived of oxygen, forceps injury, etc.

        Postnatal causes of MR:

        • brain damage: result from infections & environmental hazards
        • infections:
        • encephalitis, meningitis (infection covering the brain caused by variety of viral or bacterial agents), & pediatric AIDS
        • vaccinations reduce chances of ID
        • mosquitoes also carry diseases that sometimes causes ID
        • lead poisoning

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