Causes & Effects of Intellectual Disability

No one experiences intellectual disability the same way as someone else. Understanding the signs, symptoms and side effects of intellectual disability is a key component toward starting the recovery journey.

Understanding Intellectual Disability

Learn about intellectual disability

Intellectual disability (ID), previously known as mental retardation, is a condition in which the mental capabilities of an individual are limited. Classified as  under a group of conditions referred to as neurodevelopmental disorders, intellectual disability includes cognitive and developmental deficits that can produce impairments and hindrances in an individual’s ability to function appropriately in personal, social, academic, or occupational settings. According to the American Psychiatric Association, the range of such deficits can vary from very specific learning limitations or executive functioning control to globalized impairments of social skills or intelligence levels.

Intellectual disability typically manifests in the early stages of development, typically before a child enters grade school. Children who are faced with intellectual disability tend to reach developmental milestones at a slower pace than do those who do not have ID; for example, they typically begin walking and talking later than what is deemed developmentally appropriate. However, the signs of such disabilities tend to become most prominent once children are in an academic setting due to the fact that this is when developmental delays are most noticeable in comparison to other children of one’s own age. These children commonly struggle with interacting socially, communicating appropriately, and functioning at the expected academic level for their age. Despite such limitations, when children and adolescents have intellectual disability, it does not mean that they are incapable of mastering new skills or learning how to support themselves on a day-to-day basis. Rather, it just may take them longer to reach such skills sets. Estimates have shown that the majority of young people with ID are capable of learning academic skills up to a sixth grade level and can obtain success at developing social and communication skills as they grow into adults.

Although intellectual disability cannot be cured, when a diagnosis is provided early in a child’s life and interventions are properly implemented, children with this condition are able to achieve a high quality of life, despite any existing impairments. Early interventions and ongoing support can allow children to improve their adaptive functioning and learn many skills that will allow them to thrive in life; skill that will allow them to reach their full potential.


Intellectual disability statistics

Extensive research has concluded that intellectual disabilities affect about 6.5 million individuals throughout the United States. Of that population, approximately 85% have what is termed as mild intellectual disability. According to the American Psychiatric Association, severe intellectual disability is estimated to affect approximately six out of every 1,000 people.

Causes and Risk Factors

Causes and risk factors for intellectual disability

There are a number of factors that can play a role in the development of intellectual disability. Any time that something occurs that interferes with normal brain development, there is an increased risk that there will be an onset of this condition. While there are some instances in which an exact, specific cause for the onset of ID can be determined, on average, this only occurs about one-third of the time. Researchers believe that the following factors can come into play when determining the cause of intellectual disability:

Genetic: There are cases in which the presence of intellectual disability is due to the presence of abnormal genes that have been inherited from family members. In other cases, if errors occur when genes are being combined during prenatal development, ID can result. It is estimated that in approximately 25% of cases, intellectual disability is the result of metabolic abnormalities or chromosomal abnormalities, such as those that cause Fragile X syndrome and Down syndrome.

Physical: When individuals are afflicted by certain infections or diseases and are not properly treated, there is a risk that ID can develop. Additional physiological factors, such as extreme malnutrition, being denied appropriate medical care, or being exposed to poisonous substances like lead or mercury, can also place one at risk for developing intellectual disability.

Environmental: Environmental factors, especially those that occur prenatally, can also place individuals at risk for developing intellectual disability. In regards to prenatal risks, being exposed to radiation during the first trimester, maternal malnutrition during pregnancy, and alcohol use by the mother can all place an infant at a high risk of developing ID. Additionally, there are certain problematic circumstances that can occur during childbirth that can heighten one’s risk for developing ID, such as oxygen deprivation or being born extremely prematurely. Additional environmental factors that can place one at risk for developing intellectual disability can include experiencing a traumatic brain injury, suffering from severe malnutrition, and suffering from a near-drowning experience.

Risk Factors:

  • Genetic errors or mutations occurring during prenatal development
  • Complications arising during childbirth
  • Malnutrition
  • Exposure to extreme malnutrition, both prenatally and post-birth
  • Contacting certain illnesses or infections
  • Almost drowning
  • Prenatal exposure to drugs and/or alcohol

Signs and Symptoms

Signs and symptoms of intellectual disability

The signs and symptoms that may indicate that a child is struggling with intellectual disability can be vast. Some may become apparent during infancy, while others may not be noticeable until a child enters school. The severity of the condition, which can range from mild to profound, will play a large role in the time frame during which symptoms will present. Examples of various signs and symptoms that may be indicative of the presence of intellectual disability can include:

  • Late to roll, sit up, or walk, as compared to what is considered developmentally appropriate
  • Speech is delayed
  • Has difficulty in mastering tasks such as potty-training, dressing oneself, and/or feeding oneself
  • Shows difficulty or delays in learning
  • Struggles with problem-solving
  • Struggles with logical thinking
  • Has memory difficulties
  • Is unable to connect actions with their consequences
  • Does not appear to understand or pick up on social cues
  • Presence of health problems such as motor handicaps, hearing and vision concerns, and seizures (in those with severe or profound ID)

As was previously mentioned, the level of severity of intellectual disability can vary. Such levels are typically grouped into four distinct categories, including mild, moderate, severe, and profound. The following includes descriptions of what can be expected at each level of severity:


  • IQ score between 50 and 70
  • Is able to develop reading and math skills up to grades 3-6
  • Has difficulties regulating emotions and behaviors in age-appropriate manners
  • Typically functions at an age-appropriate level in regards to self-care
  • Is able to acquire practical skills and daily task skills
  • Is able to conform socially, yet social interactions are typically immature when compared to peers
  • Develops at a slower pace than is developmentally appropriate


  • IQ score between 35 and 49
  • Presence of unusual physical signs
  • Conceptual skills are markedly behind those of peers
  • Spoken language is primary social communication tool, but is much less complex than peers
  • Is capable of understanding elementary level health and safety skills
  • Is capable of being taught simple self-care routines and can typically participate in them without assistance


  • IQ score between 20 and 34
  • Attainment of conceptual skills is highly limited
  • Has little or no communication skills, however, is able to understand some speech and can provide some, however minimal responses
  • Typically requires support for all activities of daily living
  • Typically requires supervision at all times as they are not capable of making responsible decisions regarding the wellbeing of themselves or others
  • The acquisition of skills requires long-term teaching, as well as ongoing, consistent support


  • IQ score of less than 20
  • Presence of extreme cognitive abnormalities
  • Conceptual skills are highly limited
  • Has extremely limited understanding of symbolic communication in speech or gesture
  • Presence of sensory and physical impairments
  • Presence of motor impairments
  • Is dependent on others for all aspects of daily physical care, health, and safety


Effects of intellectual disability

When provided with appropriate interventions and support, children and adolescents with intellectual disability can go on to live happy, healthy, and full qualities of life. However, they will all inevitably face various challenges. Such challenges may include the following:

  • Memory problems
  • Attention problems
  • Difficulties interacting socially
  • Impaired self-esteem or lowered sense of self-worth
  • Difficulties finding and maintain employment as adults
  • Being unable to live on one’s own due to required assistance and supervision
  • Presence of additional medical concerns

Co-Occurring Disorders

Intellectual disability and co-occurring disorders

When children and adolescents have intellectual disability, they are believed to be 3-4 times more likely to have co-existing mental health conditions than are the general populations. Some of the most commonly cited co-occurring disorders and conditions said to present alongside ID include the following:

  • Mood disorders
  • Anxiety disorders
  • Depressive disorders
  • Impulse control disorders
  • Attention-deficit/hyperactivity disorder
  • Autism spectrum disorder
  • Aggression
  • Self-harm
What Past Clients Say

My husband and I decided to help our daughter get counseling at DBI and are so glad we made the choice to do so. Through the specialized programming that focused on behavioral therapy, our daughter is thriving so much more than before!

– Mother of a former client