Intellectual Disability: Symptoms, Causes and Treatment

The term “intellectual disability” is replaced by “mental retardation” by DSM-V as it has negative connotations, is offensive and raises misunderstandings about the nature of the disorder. Intellectual Disability refers to cognitive deficits in intellectual functioning – intelligence, reasoning, planning, abstract thinking and judgement, and deficits in functional and adaptive skills. A common misconception is that IQ tests assess intellectual disability, but the IQ of an individual is not an exclusive criterion. An individual with average or above average IQ can also have deficits in other areas of functioning, or others with a low IQ may have exceptional skills in other areas and might not meet the diagnostic criteria.

Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5), published by the APA, classifies intellectual disabilities formally called “intellectual developmental disorders” as neurodevelopmental disorders that begin during childhood and are characterized as intellectual difficulties which impair an individual’s general mental abilities.


The diagnosis of intellectual disability occurs after obtaining the history, using information from a standardized academic assessment, and a standardized measure of adaptive function indicating that a child is significantly below the expected level in social adaptation and intelligence quotient (IQ). Some of the symptoms
contributing to intellectual disability are as follows:

  • Delayed or slowed learning in school or daily activities
  • Difficulties in reasoning and problem-solving
  • Slow speed of reading
  • Not able to focus and concentrate
  • Slow in learning instructions like toilet training and self-cleaning activities
  • Difficulty in making friends and limited understanding of social relationships.

Classification of Severity

The severity of intellectual disability can be classified into “mild to moderate”, “profound”, and “severe” categories. The majority of the individuals are diagnosed with mild intellectual disability. These individuals have difficulties in learning academic skills involving reading, writing, arithmetic, time or money, abstract thinking, executive function and short-term memory are impaired. They can learn practical skills and function with minimal level of support.

Individuals with a moderate disability can care for themselves, travel to familiar places, and learn basic skills. Peoples with severe disability have major delays in development, and they can learn simple daily routines and care for themselves but need supervision. Individuals with a profound disability have congenital syndromes and cannot live independently. They require close supervision and support.


The causes or etiologic factors in intellectual disability can be genetic, developmental, environmental, or a combination.

1. Genetic factors:

Genetic factors include chromosomal and inherited conditions. Some of the genetic factors that contribute to intellectual disability are as follows:

  • Fragile X syndrome is one of the commonest genetic causes of intellectual disability. Persons with Fragile X syndrome have an increased chance of ADHD.
  • Another cause is abnormalities in the autosomal chromosomes (non-sex chromosomes). Abnormalities in sex chromosomes (X & Y) can cause physical syndromes that don’t include intellectual disability. For example, children with Turner syndrome have average to superior intelligence.
  • Down syndrome, which is caused by an extra copy of chromosome 21and is one of the most discussed syndrome in intellectual disability.
2. Acquired and Developmental Factors:

The development of the fetus includes the mother’s physical, psychological, and nutritional health during pregnancy. Many illnesses and conditions during pregnancy, such as diabetes, hypothyroidism, rubella infection and long-term use of alcohol and drugs, can cause intellectual disability in children. Complications during birth, such as lack of oxygen (hypoxia), premature birth and brain injuries, can also become causal factors.

3. Environmental and Sociocultural Factors:

These include deprivation of nutrition and nurturance, poor prenatal environment and poor postnatal medical care. Children who have been through these conditions are at risk of other psychiatric disorders like mood disorders, posttraumatic stress disorder (PTSD) and ADHD. Teenage pregnancies, low birth weight, malnutrition, and exposure to toxic substances such as lead can also contribute to intellectual disability. Childhood neglect and abuse can also be a cause of disabilities.

Tests and Assessments

  • Intelligence tests, along with diagnostic and laboratory tests can help with diagnosis.
  • Some of these tests include chromosomal analysis, urine and blood testing for metabolic disorders, and neuroimaging.
  • Chorionic villi sampling (CVS) is a screening technique to determine fetal chromosomal abnormalities.
  • Neuroimaging studies with populations of intellectually disabled patients include computerized tomography (CT), magnetic resonance imaging (MRI), functional MRI (fMRI), and diffusion tensor imaging (DTI) can also be helpful.
  • Genetic counselling can help identify genetic conditions causing or contributing to intellectual disabilities and can prevent or limit complications related to these underlying conditions.


The treatment for these children combines an assessment of social, educational, psychiatric, and environmental needs. Some of the interventions include:

a) Primary Prevention:

Education to the general public to prevent ID, including no alcohol use during pregnancy, upgrading public health policies, and optimal maternal and child health care. Family and genetic counselling can also help. Screening babies for PKU (phenylketonuria) and providing a proper diet if PKU is present can alter the emergence of intellectual disability.

b) Educational Interventions:

Educational settings for children with intellectual disability should include a program for improving their adaptive skills, social skills and vocational training. Educating the families of children or adolescents with intellectual disability to improve their competence and self-esteem and have realistic expectations for the child.

c) Behavioural and Cognitive Interventions:

Behavior therapy improves and shapes their social behaviours and controls their destructive and aggressive behaviours.
Positive reinforcement for desired behaviours and gentle punishment for undesirable behaviours has also been helpful. Cognitive therapy to dispel false beliefs and relaxation exercises with self-instruction have also been recommended. Psychodynamic therapy decreases conflicts about expectations from families for the patient that result in persistent anxiety, rage, and depression can also be used.

d) Medications:

It can help with conditions related to or happen alongside intellectual disability. This doesn’t treat intellectual disability directly, but can help with some of the symptoms that may contribute.

Tips for Parents
  • It may be difficult for a child with intellectual disability to understand their condition as it impairs their ability to understand what’s happening to them and their surroundings.
  • Parents and caregivers are likely to identify these symptoms in their children.
  • Earliest signs can be seen when you meet your pediatricians for daily checkups.
  • Remember that your child still has goals, desires and strengths; it is important to help them identify these and give them the support and care needed.
  • Learning may come slower for your child, but you need to be patient and encourage them to learn.
  • Connecting with other parents with children with similar conditions can help you form support groups.
  • Programs that teach children how to protect themselves, take care of themselves, and motivate them to engage in social relationships can also be helpful.
American Psychiatric Association. (2022). Diagnostic and statistical manual of mental disorders (5th ed., text rev.).
Kaplan, Harold I., et al. Kaplan & Sadock’s Synopsis of Psychiatry. Edited by Robert Joseph Boland and Marcia L. Verduin, Twelfth edition., Wolters Kluwer, 2022.

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