Intellectual Disability.

Intellectual disability (ID) is a disorder evident in childhood as significantly below-average intellectual and adaptive functioning. People with Intellectual disability (ID) experience difficulties with day-to-day activities to an extent that reflects both the severity of their cognitive deficits and the type and amount of assistance they receive.

DSM-5 identifies difficulties in three domains: conceptual (e.g., skill deficits in areas such as language, reasoning, knowledge, and memory), social (e.g., problems with social judgment and the ability to make and retain friendships), and practical (e.g., difficulties managing personal care or job responsibilities).

People with Intellectual disability display a broad range of abilities and personalities. Individuals who have mild or moderate impairments, can, with proper preparation, carry out most of the day-to-day activities expected of any of us. Many can learn to use mass transportation, purchase groceries, and hold a variety of jobs. Those with more severe impairments may need help to eat, bathe, and dress themselves, although with proper training and support they can achieve a degree of independence. These individuals experience impairments that affect most areas of functioning. Language and communication skills are often the most obvious.

People with more severe forms of ID may never learn to use speech as a form of communication, requiring alternatives such as sign language or special communication devices to express even their most basic needs. Because many cognitive processes are adversely affected, individuals with intellectual disability have difficulty learning, the level of challenge depending on how extensive the cognitive disability is.


Diagnostic Criteria for Intellectual Disability (Intellectual Developmental Disorder).

Intellectual disability (intellectual developmental disorder) is a disorder with onset during the developmental period that includes both intellectual and adaptive functioning deficits in conceptual, social, and practical domains. The following three criteria must be met:

A. Deficits in intellectual functions, such as reasoning, problem solving, planning, abstract thinking, judgment, academic learning, and learning from experience, confirmed by both clinical assessment and individualized, standardized intelligence testing.

B. Deficits in adaptive functioning that result in failure to meet developmental and sociocultural standards for personal independence and social responsibility. Without ongoing support, the adaptive deficits limit functioning in one or more activities of daily life, such as communication, social participation, and independent living, across multiple environments such as home, school, work, and community.

C. Onset of intellectual and adaptive deficits during the developmental period.

Types of Intellectual Disabilities.

1. Fragile X syndrome

Fragile X syndrome is the most common known cause of an inherited intellectual disability worldwide. It is a genetic condition caused by a mutation (a change in the DNA structure) in the X chromosome.

People born with Fragile X syndrome may experience a wide range of physical, developmental, behavioral, and emotional difficulties, however, the severity can be very varied.

Some common signs include a developmental delay, intellectual disability, communication difficulties, anxiety, ADHD, and behaviors similar to autism such as hand flapping, difficulty with social interactions, difficulty processing sensory information, and poor eye contact.

2. Down syndrome

Down syndrome is not a disease or illness, it is a genetic disorder which occurs when someone is born with a full, or partial, extra copy of chromosome 21 in their DNA.

People with Down syndrome can have a range of common physical and developmental characteristics as well as a higher than normal incidence of respiratory and heart conditions.

Physical characteristics associated with Down syndrome can include a slight upward slant of the eyes, a rounded face, and a short stature. People may also have some level of intellectual and learning disabilities, but this can be quite different from person to to another.


There are literally hundreds of known causes of intellectual disability, including the following:

Environmental: For example, deprivation, abuse, and neglect

Prenatal: For instance, exposure to disease or drugs while still in the womb

Perinatal: Such as difficulties during labor and delivery Postnatal: For example, infections and head injury, heavy use of alcohol among pregnant women can produce a disorder in their children called fetal alcohol syndrome, a condition that can lead to severe learning disabilities. Other prenatal factors that can produce ID include the pregnant woman’s exposure to disease and chemicals and poor nutrition. In addition, lack of oxygen (anoxia) during birth and malnutrition and head injuries during the developmental period can lead to severe cognitive impairments.


  • difficulty speaking or reading
  • difficulty understanding or following social rules or cues
  • difficulty understanding the results or consequences of their actions
  • difficulty solving problems, thinking logically, or thinking abstractly
  • difficulty planning or following schedules or routines
  • difficulty remembering things
  • difficulty letting others know their needs
  • difficulty understanding systems such as the need to pay for things, time, or how to use a phone
  • difficulty with social skills
  • a reduced ability to perform regular personal care, such as eating, getting dressed, or completing household tasks
  • limited functioning in one or more daily activities.

Treatment of Intellectual Disability

Biological treatment of ID is currently not a viable option. Generally, the treatment of individuals with ID parallels that of people with more severe forms of autism spectrum disorder, attempting to teach them the skills they need to become more productive and independent. For individuals with mild ID, intervention is similar to that for people with learning disorders. Specific learning deficits are identified and addressed to help the student improve such skills as reading and writing.

At the same time, these individuals often need additional support to live in the community. For people with more severe disabilities, the general goals are the same; however, the level of assistance they need is often more extensive. Remember that the expectation for all people with ID is that they will in some way participate in community life, attend school and later hold a job, and have the opportunity for meaningful social relationships.


David H. Barlow, V. Mark Durand. Abnormal Psychology, An Integrative Approach. (7th ed).

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