Signs, Symptoms, & Causes of Intellectual Disability

Learn about intellectual disability

Intellectual developmental disorder, also known as intellectual disability (ID) and formerly known as mental retardation (MR), is a disorder that is characterized by the presence of deficits in a person’s general mental abilities. These deficits are present in areas such as reasoning, problem-solving, abstract thinking, judgment, planning, academic learning, and learning from experience. When a person has ID, he or she will also struggle with impairments in adaptive functioning, which can lead to a failure in meeting the developmental standards that are necessary for an individual to develop appropriate social responsibility and personal independence.

The onset of intellectual disabilities typically occurs during the developmental periods and the features will depend upon the etiology and severity of the brain dysfunction. Delays in motor functioning, language abilities, and social milestones may be identifiable within the first two years of a child’s life if he or she has more severe intellectual disabilities. Mild intellectual disability may not be identifiable until the child reaches school-age when challenges with academic learning become present. Early diagnosis and ongoing interventions can improve adaptive functioning throughout one’s childhood, teen years, and adulthood. The extent of support and ongoing interventions may allow children and teens to learn the needed skills to fully participate in all activities of daily living and lead a productive, happy life.

Intellectual disability statistics

Researchers in the field believe that intellectual disabilities affect about 1% of the population in the United States. Of those affected, about 85% have mild intellectual disability. The prevalence of severe intellectual disability is estimated by the American Psychiatric Association to be approximately 6 per 1,000 people.

Causes and risk factors for intellectual disability in children and teens

Researchers believe that anything that leads to interference with normal development of the brain can lead to intellectual disability. The most common causes and risk factors include:

Genetic: When a person inherits abnormalities of genes from his or her parents, the result can be the development of intellectual disability. These abnormalities can form if there are errors in the combination of genes during prenatal development. Intellectual disabilities can also result from other disorders of the genes that may be caused during pregnancy, including things such as infections or being overly exposed to x-rays. Chromosomal disorders, caused by the presence of too few or too many chromosomes, can also impact the development of ID.

Physical: Most people who have intellectual disabilities have no discernable structural abnormalities of the brain. However, in about 10-15% of people, malformations in the central nervous system, such as dysfunction in the cortical structures, are identified. The most common malformations consist of neural tube defects (anencephaly, encephalocele, or spina bifida) and microcephaly.

Environmental: Problems during pregnancy that interfere with fetal brain development including drug or alcohol use, maternal malnutrition, preeclampsia, and infections during pregnancy can lead to the development of ID. Problems during childbirth, including extreme prematurity and oxygen deprivation increase the risk for intellectual disabilities as well. Additionally, traumatic brain injuries, the presence of illnesses that affect the brain, exposure to toxins such as lead, extreme malnutrition, and near-drowning have the potential to cause the onset of intellectual disabilities.

Risk Factors:

• Prenatal alcohol or drug exposure
• Contraction of illnesses or infections while in utero
• Not receiving enough oxygen during birth
• Suffering head injuries
• Malnutrition
• Parental low IQ

Signs and symptoms of intellectual disability in children and teens

The signs and symptoms of intellectual disability will vary tremendously from person to person depending upon the severity of the disability, the underlying cause for the disability, the implementation of appropriate interventions, and co-occurring disorders. Signs and symptoms are broken down by level of severity.

Early signs and symptoms of intellectual disability:

• Children may have trouble recalling things
• Child may reach developmental milestones later than same-age peers, such as rolling over, sitting up, crawling, or walking
• Have trouble speaking or experiencing delays in speech
• Trouble understanding social norms
• Challenges with problem-solving and logical thinking
• Behavioral problems like extreme temper tantrums
• Having difficulty understanding the results of his or her actions

Signs and symptoms of mild intellectual disability:

Conceptual symptoms:

• Preschool aged-children may show no conceptual symptoms
• School-aged children may have difficulties learning academic skills such as reading, writing, math, time, or money
• Older children, teens, and adults may have impairment in short-term memory, abstract thinking, planning, organizing, setting priorities as well as functional use of academic skills

Social symptoms:

• Immature social interactions with peers
• Difficulties understanding social skills
• Communication, conversation, and language immaturity
• Challenges with emotional regulation
• Being easily manipulated

 Practical symptoms:

• May function age-appropriately in personal care
• Requires some support for complicated activities of daily living as compared to peers Recreational skills are not age-appropriate

Signs and symptoms of moderate intellectual disability:

Conceptual symptoms: all fall markedly behind those of same-age peers

• Preschool-aged children experience slowed development of language and pre-academic skills
• School-aged children experience significantly limited progress in reading, mathematics, writing, and understanding the concept of time and money as compared to peers
• Teens function at an elementary level and need support using academic skills in work and everyday life

Social symptoms:

• Primary communication tool is spoken language but is much less complex than peers
• Person is able to maintain friendships and romantic relationships, although they may be limited due to social and communication limitations
• May not interpret social cues properly
• Decision-making abilities are limited

Signs and symptoms of severe intellectual disability:

Conceptual skills:

• Limited understanding of conceptual skills
• Little to no understanding of written language, concepts using numbers, quantity, time, and money
• Caregivers must provide extensive support for problem solving throughout life

Social skills:

• Spoken language, vocabulary, and grammar is markedly limited
• Speech may include only single words or phrases
• Speech is focused upon the present and everyday events
• Language used primarily for communication rather than explanation
• Person does understand speech and gestures in communication

Practical skills:

• Requires assistance for all activities of daily living including eating, dressing, bathing, and toileting
• Learning new skills involves long-term teaching and ongoing care
• Needs constant supervision
• Cannot make decisions regarding well-being of him or herself or others

Signs and symptoms of profound intellectual disability:

Conceptual skills:

• Conceptual skills usually encompass the physical world rather than symbolic processes
• Objects may be used in a goal-directed manner for self-care, work, and leisure. However, people who have co-occurring motor and sensory impairments may be unable to properly use physical objects.
• May be able to learn visuospatial skills such as matching objects based upon physical features

Social skills:

• Very limited comprehension of symbolic communication in words or gestures
• May be unable to understand some instructions or gestures
• Non-verbal, non-symbolic communication techniques used to make needs and emotions known
• Co-occurring sensory and physical impairment may hamper social abilities

Practical skills:

• Dependent upon others for all aspects of physical care, health, and safety, although he or she may be able to participate in some of these activities with assistance
• Simple actions with objects may be the way a person participates in activities
• Co-occurring physical and sensory impairments are often barriers to participation in some home, recreational, and vocational activities

Effects of intellectual disability in children and teens

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

Intellectual disability and co-occurring disorders

There are a number of disorders that co-occur in people who have intellectual disabilities. The most common co-occurring, comorbid disorders include:

• Attention-deficit/hyperactivity disorder (ADHD)
• Depressive disorders
• Anxiety disorders
• Bipolar disorder
• Autism spectrum disorders (ASDs)
• Stereotypic movement disorder
• Impulse control disorders
• Major neurocognitive disorder
• Self-injury