Intellectual Disability – Classifications, Effects and Treatment

Overview of Intellectual Disability

Intellectual disability (ID), previously known as mental retardation, is a term that is used when an individual has below-average intelligence or mental ability. Lack of skill necessary for day-to-day living are also commonly associated with this type of disorder. When it comes to intellectual disability, there are varying degrees ranging from mild to severe. While children and adolescents with intellectual disability are able to learn new skills, they do so at a slower rate than others. These children often have a hard time communicating their specific wants and needs, and usually struggle with taking care of themselves. In most cases, these individuals need assistance with speaking, walking, dressing, and eating.

Usually delays in motor functioning, language abilities, and social milestones can be identified within the first two years of a child’s life if he or she has more severe intellectual disabilities. However, mild intellectual disability may not be identifiable until the child reaches school-age, when challenges with academic learning become present. While it typically occurs during the developmental periods, it is also possible for intellectually disability to develop later as the result of illness or brain injury.

Intellectual disability is not a disease and cannot be cured, however early diagnosis and ongoing interventions can improve adaptive functioning throughout one’s childhood and into adulthood. With ongoing support and interventions, children with intellectual disability can learn to do many things.

Classifications of Severity

The terms “mild,” “moderate,” “severe,” and “profound” have been used to describe the severity of the condition. This approach has been helpful in that aspects of mild to moderate ID differ from severe to profound ID. The DSM-5 retains this grouping with more focus on daily skills than on specific IQ range.

Mild to Moderate Intellectual Disability

The majority of people with ID are classified as having mild intellectual disabilities. Individuals with mild ID are slower in all areas of conceptual development and social and daily living skills. These individuals can learn practical life skills, which allows them to function in ordinary life with minimal levels of support. Individuals with moderate ID can take care of themselves, travel to familiar places in their community, and learn basic skills related to safety and health. Their self-care requires moderate support.

Severe Intellectual Disability

Severe ID manifests as major delays in development, and individuals often have the ability to understand speech but otherwise have limited communication skills. Despite being able to learn simple daily routines and to engage in simple self-care, individuals with severe ID need supervision in social settings and often need family care to live in a supervised setting such as a group home.

Profound Intellectual Disability

Persons with profound intellectual disability often have congenital syndromes. These individuals cannot live independently, and they require close supervision and help with self-care activities. They have very limited ability to communicate and often have physical limitations. Individuals with mild to moderate disability are less likely to have associated medical conditions than those with severe or profound ID.

Prevalence of Intellectual Disability

The prevalence of intellectual disability in developing countries is estimated to range from 10 to 15 per 1000 children; of those, about 85% have a mild intellectual disability. From 1 to 3% of the Western population is estimated to have an intellectual disability. Incidence is challenging to accurately calculate as mild disabilities may be under-recognized until later in childhood. Intellectual disability is reported to peak at the ages of 10 to 14 years and is 1.5 times more prevalent in males than females.


The psychophysiology of intellectual disability involves the intricate interplay between neurological, cognitive, and physiological factors. Individuals with intellectual disabilities often exhibit abnormalities in brain structure and function, impacting their cognitive processes. Neurologically, variations in brain development, including structural anomalies or disruptions in neural connectivity, contribute to limitations in intellectual functioning. These deviations can be attributed to genetic factors, prenatal or perinatal complications, and environmental influences. Physiologically, these neurological differences may lead to challenges in information processing, memory, and problem-solving skills, reflecting the psychophysiological underpinnings of intellectual disability. Understanding the intricate relationships between brain structure, cognitive processes, and physiological functioning is crucial for developing targeted interventions and support strategies to enhance the quality of life for individuals with intellectual disabilities.

Causes of Intellectual Disability

Intellectual disability can be caused by a variety of factors, including injury, disease, or an issue with brain development. Chromosomal defects such as variants and inborn errors of metabolism can permanently alter cognitive function. Intellectual disabilities arise from such factors as:

  • Down syndrome, the most common cause of ID in the United States
  • Fragile X syndrome, the most commonly known congenital (present at birth) cause of ID
  • Dravet syndrome, a rare congenital cause of ID
  • Huntington’s disease, a hereditary cause of late-onset ID

Intellectual and developmental disabilities also stem from cognitive disruption due to:

  • Brain malformations
  • Prenatal alcoholor toxin exposure
  • Prenatal nutritional deficiencies
  • Maternal infections or complications leading to brain injury
  • Pre- or postnatal brain infections


Symptoms of ID will vary based on your children’s level of disability and may include:

  • Failure to meet intellectual milestones
  • Sitting, crawling, or walking later than other children
  • Problems learning to talk or trouble speaking clearly
  • Memory problems
  • Inability to understand the consequences of actions
  • Inability to think logically
  • Childish behavior inconsistent with the children’s age
  • Lack of curiosity
  • Learning difficulties
  • IQ below 70
  • Inability to lead a fully independent life due to challenges communicating, taking care of themselves, or interacting with others

If your child has ID, they may experience some of the following behavioral issues:

  • Aggression
  • Dependency
  • Withdrawal from social activities
  • Attention-seeking behavior
  • Depression during adolescent and teen years
  • Lack of impulse control
  • Passivity
  • Tendency toward self-injury
  • Stubbornness
  • Low self-esteem
  • Low tolerance for frustration
  • Psychotic disorders
  • Difficulty paying attention

Some people with ID may also have specific physical characteristics. These can include having a short stature or facial abnormalities.

Effects of Intellectual Disability

Depending upon the root cause for the disability and the severity of the symptoms, many people who have intellectual disabilities are able to live happy, fulfilled lives. There are, however, some possible negative effects of intellectual disabilities. These may include:

  • Challenges locating and obtaining basic healthcare, adequate nutrition, education, and economic stability
  • Consequences of pre-existing medical conditions
  • Participating in risky behaviors, including substance use and violent behaviors
  • Difficulties finding and maintaining gainful employment
  • Difficulties performing activities of daily living
  • Homelessness
  • Manipulation by others around the person
  • Caregiver burnout and abuse

Risk factors

Intellectual disabilities can arise from a variety of risk factors, encompassing genetic, environmental, and medical influences. Here are some key factors associated with an increased risk of intellectual disability:

  • Genetic Factors: Inherited genetic conditions, such as Down syndrome, Fragile X syndrome, and other chromosomal abnormalities, can significantly increase the risk of intellectual disability. Genetic mutations or abnormalities can disrupt normal brain development and functioning.
  • Prenatal Exposure: Certain prenatal factors can contribute to intellectual disabilities. Exposure to teratogenic substances, including drugs, alcohol, and certain infections during pregnancy, may adversely affect fetal brain development and lead to cognitive impairments.
  • Perinatal Complications: Complications during the birth process, such as oxygen deprivation, premature birth, or low birth weight, can contribute to intellectual disabilities. Lack of adequate oxygen to the brain during delivery, in particular, can have lasting effects on cognitive function.
  • Postnatal Factors: Experiences or conditions after birth can also play a role. Head injuries, infections, and exposure to toxins in the postnatal period can impact brain development and contribute to intellectual disabilities.
  • Illnesses and Infections: Certain illnesses and infections, especially those affecting the central nervous system, can increase the risk of intellectual disabilities. Examples include meningitis, encephalitis, and severe cases of lead poisoning.
  • Malnutrition: Inadequate nutrition, particularly during critical periods of brain development, can lead to intellectual disabilities. Malnutrition may result from poverty, lack of access to nutritious food, or other socio-economic factors.
  • Environmental Deprivation: Lack of stimulation and a nurturing environment during early childhood can contribute to intellectual disabilities. Children need a supportive and stimulating environment to develop cognitive and adaptive skills.
  • Social and Economic Factors: Low socio-economic status, limited access to quality healthcare, and educational resources can contribute to intellectual disabilities. Children in disadvantaged environments may face challenges that affect their cognitive development.

Understanding these risk factors is crucial for prevention, early intervention, and providing appropriate support and resources to individuals and families affected by intellectual disabilities.

Diagnostic criteria for intellectual disability

To diagnose an intellectual disability, the following criteria must be met:

  • Limited intellectual functioning: This is typically measured with an IQ test. A test score lower than 70 is usually indicative of limited intellectual functioning.
  • Limited adaptive skills: Here, a person with an intellectual disability will struggle with social and practical skills needed for daily functioning. These include conceptual skills like reading or writing, social skills like communication or problem solving, and practical skills like eating, walking, or getting dressed.
  • The onset of symptoms before the age of 18: This condition typically develops in childhood. While it ranges in severity, some early signs delayed motor skills, struggle with problem-solving, difficulty remembering things, and delayed speech.

Some research shows that about 20-35% of people who have an intellectual disability are also likely to develop other mental health conditions like anxiety or depression. In determining your child’s diagnosis, several tests might be ordered by your healthcare provider and the team of specialists taking care of your child. These tests include:

  • Neurological tests such as an electroencephalogram (EEG) or magnetic resonance imagining (MRI) to determine if there are any abnormalities in the brain
  • Genetic tests to help identify if there is an inherited disorder like Fragile X syndrome that could cause intellectual disability
  • General medical tests depending on the symptoms your child is exhibiting
  • Special education tests
  • Developmental screening tests to determine your child’s level of intellectual and social functioning
  • Prenatal screening to determine if there are any developmental challenges while a parent is still pregnant
  • A hearing evaluation in case a hearing problem is responsible for the impaired intellectual functioning and not an intellectual disability.

Treatment and management

There’s no way to cure or treat intellectual disability directly. With good treatment, individuals with intellectual disability can have a good quality of life. The treatments focus on helping with adaptive behaviors and life skills.

Treatment types include:

  • Education support and interventions. These can help with changes to educational programs and structure. An example of educational support is an Individualized Education Plan (IEP), which creates a custom educational plan and expectations.
  • Behavioral support and interventions. These kinds of interventions can help with learning adaptive behaviors and related skills.
  • Vocational training. This can help people with intellectual disabilities learn work-related skills.
  • Family education. This can help family and loved ones of those with intellectual disability learn more about intellectual disability and how to support a loved one who has it.
  • Various medications can help with conditions that are related to or happen alongside intellectual disability. While these don’t treat intellectual disability itself, they can help with some of the symptoms that may contribute.
  • Community support. A person and/or their family can contact local government agencies or support organizations. Doing so can help them get access to the services they benefit from, including supports in home or work environments and options for daytime activities.


While it may not be possible to prevent all cases of intellectual disabilities, there are steps that can be taken to minimize the risk and promote healthy development. Here are some strategies:

Genetic: Genetic counseling and screening during pregnancy can help parents understand risks and make plans and decisions.

Social: Nutrition programs can reduce disability associated with malnutrition. Early intervention in situations involving abuse and poverty will also help.

Toxic: Preventing exposure to lead, mercury, and other toxins reduces the risk of disability. Teaching women about the risks of alcohol and drugs during pregnancy can also help reduce risk.

Infectious diseases: Certain infections can lead to intellectual disability. Preventing these diseases reduces the risk. For example, rubella syndrome can be prevented through vaccination. Avoiding exposure to cat feces that can cause toxoplasmosis during pregnancy helps reduce disability from this infection.

About DiseasesDic

Check Also

Misophonia – Definition, Causes, Treatment and Prevention

Definition Misophonia, also known as the “hatred or dislike of sound,” is characterized by the …

Leave a Reply

Your email address will not be published. Required fields are marked *