Intellectual Disability (Intellectual Developmental Disorder)

Intellectual developmental disorder is a disorder marked by below-average intellectual function and a lack of developmental skills.  A neurodevelopmental disorder, intellectual developmental disorder can cause impairments in an individual’s cognitive function, capacity for adaptive behavior,1 and ability to learn. Some symptoms2 of intellectual developmental disorder include:

• Delayed learning (in school or in home environment)

• Does not meet intellectual developmental markers

• Social immaturity when compared to peer group

• Limited spoken language

• Requires support in activities of daily living as compared with peer group

• Difficulty with problem-solving

• Has difficulty controlling behavior and emotions

• Lack of fear or apprehension when encountering new people 

• Good-natured disposition 

• Difficulties with abstract thinking, problem-solving, and generalizing information from one situation to another

The four categories of severity for intellectual development disorder are mild, moderate, severe, and profound. The level of severity of the disorder depends on the degree to which symptoms interfere with the individual’s ability to meet the demands of daily life compared to their peer group. 

There are also some behavioral traits associated with intellectual development disorder, though they are not classified as criteria for diagnosis. These include:

• Impulsivity

• Aggression

• Passivity

• Self-injury

• Dependency

• Low tolerance for frustration

• Low self-esteem

• Gullibility

• Resilience

Very often, individuals with intellectual disabilities (sometimes incorrectly referred to as the intellectually disabled) also have other impairments from comorbid medical, neurodevelopmental, or psychological conditions. This is because by definition, intellectual developmental disorder describes a situation where an intellectual disability and other disabilities are present at the same time. 

The causes of intellectual disability can range as widely as the presentation of symptoms. In some cases, there may even be multiple factors contributing to the intellectual disability. Factors that can contribute to intellectual developmental disorder may be classified into three categories: pre-birth, birth, or early childhood. 

Some pre-birth contributing factors to intellectual and developmental disabilities can include:

• Infections that interfere with fetal development, such as rubella or toxoplasmosis 
• Genetic mutations, such as changes in the FMR1 gene that can cause fragile X syndrome—a common source of intellectual and developmental disabilities
• Medical conditions in the mother during pregnancy, such as hypothyroidism
• Teratogens such as radiation exposure, alcohol, drugs, or tobacco

Some factors during birth that may contribute to intellectual or developmental disability include:

• Premature birth
• Hypoxia (lack of oxygen) during birth
• Other brain injuries 

Early childhood factors that may contribute to intellectual or developmental disability include:

• Exposures to toxins or heavy metals like mercury
• Brain damage from injury or accident
• Childhood infections that spread to the nervous system (i.e., meningitis)
• Brain tumors (cancerous or non-cancerous growths)
• Medical conditions like some forms of severe epilepsy may cause brain damage that leads to intellectual disability

Intellectual developmental disorder refers to neurodevelopmental conditions that affect functioning in two areas: cognitive and adaptive functioning. There is currently no cure for intellectual disability or a way to treat the disorder directly. Individualized treatment3 plans focus on the specific needs and potential of the person. Treatment typically focuses on improving life quality through adaptive behavior and developmental skills, and involves a multidisciplinary approach including educators, therapists, and medical professionals working together to provide comprehensive and coordinated care for those with intellectual disabilities or intellectual developmental disorders. Many individuals with intellectual disabilities live independently with varying levels of support.

Medication

There is no medication that is specifically approved to treat intellectual disability or intellectual developmental disorder. However, healthcare professionals may prescribe one or more of a number of medications to help manage the symptoms of any concurrent conditions the person may have such as anxiety or behavioral difficulties.

It is important to consult with a doctor or medical professional before beginning or changing any medication plan. The information provided in this article is not intended as medical advice; please consult a qualified healthcare professional for personalized guidance.  

Other treatment options

There are several interventions for the treatment of intellectual disability. These include:

• Individualized Education Plans (IEPs) offer structure and goals to help model education to the needs of the individual.
• Family education may be provided to educate family members on expectations and how best to support someone with an intellectual disability.
• Community support organizations can offer benefits such as in-home assistance, daytime activities, or work support.
• Behavioral support interventions can help with learning adaptive behaviors and social skills.
• Vocational training can help the individual learn work-related skills at their own pace.

People with intellectual disabilities or intellectual developmental disorders can continue to learn and develop skills throughout their lives with appropriate support. It can be important for families and caregivers to seek early and ongoing engagement with healthcare providers to optimize health outcomes and services for individuals with intellectual disabilities.

Therapy for intellectual disability can look different depending on who is receiving it. For those with milder forms of intellectual disability, therapy can be used to build self-esteem and help them to understand their strengths. Individuals with intellectual disabilities will have desires and goals; they just may not be able to fully process and understand the world around them. 

Family members who are caregivers for those with intellectual developmental disorder can benefit from therapy by learning self-care, stress management, and even learning how to best support a person with an intellectual disability or intellectual developmental disorder. Caregiver support and oversight can be a full-time job on top of other responsibilities in daily life. Having support for themselves can be key in avoiding caregiver burnout. 

Finally, siblings of those with intellectual disabilities can have a unique set of challenges. They may perceive that they don’t receive enough attention, have feelings of guilt that they are “normal,” and deal with embarrassment stemming from negative peer interactions. Attending therapy through a platform like BetterHelp and having someone to guide and listen to them as they navigate these feelings can be beneficial. 

Additional resources for intellectual developmental disorder

Here are some other resources for those with intellectual developmental disorder and their family members:

• Safe Return to School For All
• HHS Administration on Disabilities
• CDC: National Center On Birth Defects and Developmental Disabilities (NCBDDD)
• Association of University Centers On Disabilities (AUCD)
• The Arc
• The March Of Dimes
• The Special Olympics

In addition, social inclusion, community participation, and advocacy for rights and services can all improve the quality of life for people with intellectual disabilities or intellectual developmental disorders.

Intellectual developmental disorders are a primary focus of NICHD's research support.

A clinical primer published in 2020 reported that psychosocial and environmental factors were the main contributors to mild intellectual disability, which makes up 85% of those with intellectual disability. The authors recommend early testing for intellectual disability, including genetic and metabolic workups, as well as neuroimaging. 

A paper published in 2020 that explores parenting of individuals with intellectual disabilities or intellectual developmental disorder found that many families had their children removed from the home due to outdated ideas of parental blame and intellectual disability, despite updated knowledge. The authors recommend specific service pathways to support families with multiple impediments, starting from conception to offer opportunities for these families to grow together in a safe and nurturing environment. 

According to a study published in 2022, "most people with disabilities" score highly when tested for character strengths such as “love of learning, honesty, appreciation of beauty and excellence, kindness, and fairness.”

Here are some key statistics on intellectual developmental disorder:

• Around the world, 1%-3% of children are affected by intellectual disability.
• Intellectual disability is marginally more common in men or individuals assigned male at birth.
• In the United States, it’s estimated that 8.7 to 36.8 per one thousand people have an intellectual disability.