Children with Intellectual Developmental Disorder have deficits in general intellectual functioning that can have multiple degrees. They have difficulties with reasoning, planning, judgment, abstract thinking, and multiple types of learning. They often struggle in school and may also have problems with friends and day-to-day tasks like bathing or getting dressed. They might seem to act out or even engage in self-harm behaviors, but the problem is that they usually do not understand what behavior is appropriate or how to communicate their needs at a given time.

Children who struggle to achieve intellectual developmental milestones but are too young or otherwise unable to undergo standardized testing to measure their intellectual capacities may be diagnosed with a condition called Global Developmental Delay. Only children under age 5 years can be diagnosed in such a way.

What are the symptoms of Intellectual Developmental Disorder?

The symptoms of Intellectual Developmental Disorder involve intellectual deficits, as well as problems with understanding abstract concepts, building social skills, and managing practical tasks that determine how independent we can be in our daily lives. These deficits and problems become apparent early in a child’s development, and their severity depends on the severity of the disorder. Specific symptoms may include:

Core Symptoms

Associated Symptoms

  • Intellectual deficits including:
  • Reasoning (e.g., understanding assumptions and consequences, and making inferences)
  • Problem solving
  • Planning
  • Abstract thinking (e.g., understanding concepts and ideas)
  • Judgment (e.g., differentiating right and wrong)
  • Academics
  • Learning
  • Additional deficits that result in failures to meet developmental and social-cultural markers for independence and responsibility, including:
  • Daily life skills (e.g., communicating, socializing)
  • Gaining personal independence
  • Failing to achieve milestones such as crawling, walking, or talking, or achieving them later than other children
  • Finding it hard to remember things, solve problems, or learn and apply new information
  • Struggling to keep up at school
  • Difficulty speaking to others, reading body language, and understanding social cues
  • Having trouble making and keeping friends
  • Having trouble doing daily tasks, such as basic self-care (e.g., getting dressed, using the bathroom), household chores, or handling money
  • Having trouble connecting previously learned concepts to new problems

How is Intellectual Developmental Disorder diagnosed?

Intellectual Developmental Disorder is diagnosed ideally by a multidisciplinary team, including child-adolescent psychiatrists, developmental pediatricians, neurologists, and/or geneticists in collaboration with the family. If a caregiver has concerns about a child’s development, a child-adolescent psychiatrist will use an intelligence test to determine the child’s intellectual abilities, or intelligence quotient (IQ), a standardized metric that represents the child’s knowledge and reasoning capability. Individuals with performance on those tests which is lower than two standard deviations below the population average are found to have very low cognitive abilities that characterize children with Intellectual Developmental Disorder. While many tests are available, the most common ones are the Weschler tests, on which scores below 70, may indicate children have Intellectual Developmental Disorder. The child-adolescent psychiatrist, in close collaboration with other disciplines, will seek to confirm this diagnosis by learning more about the child through interviews with caregivers, and by administering other tests and interviews designed to measure the child’s capabilities in other areas.

Intellectual Developmental Disorder can be mild, moderate, severe or profound (see table below). Although the IQ tests guide some clues on defining the severity of the disorder, the clinician is better suited to weigh distinct aspects of the general cognitive abilities, with aspects of social and practical domains to determine the severity level of the disorder. This parallel evaluation of the child’s intelligence score along with their adaptive functioning is key in determining both the actual presence and the severity level of the diagnosis.

Severity Levels for Intellectual Developmental Disorder

Conceptual problems

Social problems

Practical Problems

Mild

Difficulties may not be obvious in preschool children, but school-age children show academic difficulties requiring support in one or more of the following areas: reading, writing, mathematics, time, currency.

The child may have immature language and communication, as well as issues with managing emotions, behavior, and social situations compared to peers. There is a risk of being manipulated by others, including peers.

The child may be able to perform some self-care activities (e.g., eating, dressing, toileting, brushing teeth, washing hands), but may need more support with more complex daily tasks (e.g., cleaning up).

Moderate

In preschool children, there are delays in language and preacademic skills development. School-age children experience academic progress that is very limited compared to peers.

The child’s language and communication skills are noticeably limited when compared to peers. Still, these children will have relationships with family and friends.

The child can perform some self-care activities (e.g., eating, dressing, toileting, brushing teeth, washing hands) with training and support. Basic home tasks can be done as well, but will likely be delayed and in need of continued support into adulthood. The child is also able to learn and participate in recreational activities.

Severe

The child has little understanding of language or of concepts including numbers, quantity, time, or money, and requires extensive caregiver support.

The child’s spoken language is very limited–often using only single words, frequently-used phrases, and gestural communication–and focused on what is happening here and now. Relationships are possible with family and other caregivers, and these relationships are potentially a source of happiness.

The child’s development of all daily living skills is very delayed, but he or she can still complete basic self-care or home chores with support. The child is able to learn and participate in basic recreational activities with support. Self-injury or other concerning behaviors may be present.

Profound

The child will struggle with not being unable to use numbers, letters, or other symbols for learning or communication, but may be able to match objects based on what they look like, and use some objects in a goal-directed manner (e.g., a brush used to brush one’s hair). However, motor or sensory problems may prevent the child from using objects in a functional way (e.g., moving a brush through one’s hair).

The child has a very limited understanding of spoken language for communication, and expresses thoughts and desires largely through gestures or other nonverbal communications. The child may understand simple, single-step instructions or gestures. Relationships with well-known caregivers are enjoyed, but motor or sensory problems may prevent social activities.

The child will remain dependent on caregivers for all aspects of daily living, although some may participate in some basic self-care or home chores with support. Recreational activities are limited, but may include listening to music, watching movies, or going for supervised walks, as well as water activities with support. Comorbid motor or sensory impairments may prevent participation in activities. Self-injury or other concerning behaviors may be present.

When administering tests and assessing for Intellectual Developmental Disorder, it is important to take into consideration that cultural aspects might obscure the real test scores. Tests need to be appropriately adapted to each culture to be valid for assessment of intelligence, and they are typically not validated in underserved or minority populations. Some intelligence tests can be administered to a child as early as at 2.5 years of age.

Intellectual Developmental Disorder Facts

Worldwide frequency of the condition

Intellectual Developmental Disorder is present in 1% of the world's population. There is no recent, specific epidemiological data for Greece.

Burden of the condition in Greece

Intellectual Developmental Disorder accounts for 0.5% for all disability adjusted life years (DALYs) lost to health conditions in Greece for 5- to 14-year-old children and adolescents. It is the 8th most prominent mental health condition adding to the health burden of the Greek child and adolescent population.

Gender ratio

Gender comparative data for Intellectual Developmental Disorder varies widely based on the severity and the broad range of co-occurring disorders. Generally, males are more likely to be diagnosed than females.

Peak age of onset

Although specific data for Intellectual Developmental Disorder is unavailable, the peak age of onset for neurodevelopmental disorders, in general, is 5.5 years of age.

Proportion of the condition that emerges before age 18

Although specific data for Intellectual Developmental Disorder is unavailable, the proportion that emerges before age 18 years for neurodevelopmental disorders, in general, is 83.2%. This means that 83.2% of individuals with a neurodevelopmental disorder will have been diagnosed by the time they are 18 years old.

What are the associated factors for Intellectual Developmental Disorder?

Intellectual Developmental Disorder is frequently associated with influences occuring during the child’s early years, like experiencing head and brain injuries or being near toxic items (e.g., lead). Some associated factors for Intellectual Developmental Disorder are summarized below:

  • Genetic and familial factors. There are a number of genetic syndromes and chromosomal disorders that may result in intellectual deficits with the most common being Down syndrome, 22q11.2 deletion syndrome, fragile X syndrome, Williams syndrome, and Prader-Willi syndrome.
  • Prenatal development factors. Premature birth, earlier than 25 weeks’ gestation.
  • Complications during pregnancy. Some maternal infections during pregnancy; a pregnant mother’s use of illegal drugs or alcohol, or exposure to toxins (e.g., lead, mercury, certain medications); or situations in which a pregnant mother is not getting enough nutrients.
  • Complications during childbirth. Severe complications such as hypoxia of the baby, hemorrhage of the delivering mother, or trauma/accident upon delivery.
  • Complications after the child is born and early in childhood. Serious brain infections (e.g., meningitis or encephalitis), severe accidents affecting their brain, recurrent seizures, or severe abuse to the child.

What other disorders co-occur with Intellectual Developmental Disorder?

Even though each child is different, neurodevelopmental and medical conditions co-occur in children with Intellectual Developmental Disorder at a rate that is three to four times higher than in the general population. The most common comorbid developmental and mental health disorders are Autism Spectrum Disorder (ASD), Attention Deficit/Hyperactivity Disorder (ADHD), depressive disorders, anxiety disorders, bipolar disorder, and conduct disorder. Common comorbid metabolic and physical disorders include hypothyroidism, seizures, cardiovascular problems, obesity, and constipation. Given this range of comorbidities, it is essential to coordinate with a pediatrician throughout childhood and adolescence to prevent, promptly identify, and/or manage any conditions. This coordination includes remaining consistent with follow-up visits, as well as early hormonal screening, routine laboratory work, and clinical assessments.

How is Intellectual Developmental Disorder treated?

Even though Intellectual Developmental Disorder is a stable condition that will accompany the child throughout his/her life, some interventions can mitigate its impacts and impairments improving quality of life and well-being. Special education and rehabilitation programs can help children learn essential social and practical skills they will need to complete school and, in some cases, live independently as adults. The earlier the identification of the problems and the assignment of a proper diagnosis to initiate management, the better the outcome will be. Various interventions are currently available, and can help families at different levels, as described below:

  • Preventing or minimizing the deterioration of associated symptoms. Following medical recommendations on regular screening and management of comorbid medical conditions can help lessen several mental health implications. Early intervention is a term used to describe a package of diagnostic and therapeutic services provided to children and families with developmental disorders, earlier than 3 years of age. Beginning services early can have exponentially more impactful results in learning, behavior and function.
  • Limiting the extent of impairment in a child’s daily life. Specialized multidisciplinary services include occupational therapy, physical therapy, speech-language therapy, family counseling. Individual, family, and group behavioral and cognitive-behavioral psychotherapy can help to improve daily life skills, as well as cognitive and social skills. Additionally, psychiatric medications could be useful in addressing possible behavioral and emotional dysregulation issues.
  • Supporting the way a child can function better and improve their overall quality of life. These interventions aim to support children and adolescents with Intellectual Developmental Disorder in their individualized educational needs, to engage them in socializing and vocational rehabilitation programs, and to prepare them for appropriate integration to the community on their journey into adulthood. Adults with mild and some with moderate Intellectual Developmental Disorder may lead independent lives.

Where to find more information

If you need more information on developmental milestones and reasons for concerns about a child's intellectual development, you can also go to our short guides "What to expect from infants and toddlers (birth to 3 years)", "What to expect from preschoolers (3 to 6 years)", "What to expect from children (6 to 12 years)", "What to expect from adolescents (12 to 18 years)", and "Early developmental concerns".

To learn more about the technical work conducted to develop this guide, please consult our reference list here:

References

Clinical description, symptoms, and diagnostic information

  • American Psychiatric Association. (2022). Diagnostic and Statistical Manual of Mental Disorders: Fifth Edition Text Revision DSM-5-TR. American Psychiatric Association Publishing, Washington, DC.
  • Child Mind Institute. (2021). Quick Guide to Intellectual Development Disorder. Child Mind Institute. Retrieved 11/17/22, from https://childmind.org/guide/quick-guide-to-intellectual-development-disorder/
  • World Health Organization. (2022). 6A00 Disorders of intellectual development. In International statistical classification of diseases and related health problems (11th ed.). https://icd.who.int/browse11/l-m/en#/http%3a%2f%2fid.who.int%2ficd%2fentity%2f605267007

Facts

  • American Psychiatric Association. (2022). Diagnostic and Statistical Manual of Mental Disorders: Fifth Edition Text Revision DSM-5-TR. American Psychiatric Association Publishing, Washington, DC.
  • Institute for Health Metrics and Evaluation (IHME). (2019). GBD Compare Data Visualization. Seattle, WA: IHME, University of Washington, Available from http:// vizhub.healthdata.org/gbd-compare. (Accessed 11/15/2022)
  • Kendler, K. S. (2013). What psychiatric genetics has taught us about the nature of psychiatric illness and what is left to learn. Molecular Psychiatry, 18(10), 1058–1066. https://doi.org/10.1038/mp.2013.50
  • Maulik, P. K., Mascarenhas, M. N., Mathers, C. D., Dua, T., & Saxena, S. (2011). Prevalence of intellectual disability: A meta-analysis of population-based studies. Research in Developmental Disabilities, 32(2), 419–436. https://doi.org/10.1016/j.ridd.2010.12.018
  • Polyak, A., Rosenfeld, J. A., & Girirajan, S. (2015). An assessment of sex bias in neurodevelopmental disorders. Genome Medicine, 7(1), 94. https://doi.org/10.1186/s13073-015-0216-5
  • Solmi, M., Radua, J., Olivola, M., Croce, E., Soardo, L., Salazar de Pablo, G., Il Shin, J., Kirkbride, J. B., Jones, P., Kim, J. H., Kim, J. Y., Carvalho, A. F., Seeman, M. V., Correll, C. U., & Fusar-Poli, P. (2022). Age at onset of mental disorders worldwide: Large-scale meta-analysis of 192 epidemiological studies. Molecular Psychiatry, 27(1), 281–295. https://doi.org/10.1038/s41380-021-01161-7

Associated factors

  • American Psychiatric Association. (2022). Diagnostic and Statistical Manual of Mental Disorders: Fifth Edition Text Revision DSM-5-TR. American Psychiatric Association Publishing, Washington, DC.
  • Glasson, E. J., Buckley, N., Chen, W., Leonard, H., Epstein, A., Skoss, R., Jacoby, P., Blackmore, A. M., Bourke, J., & Downs, J. (2020). Systematic review and meta-analysis: Mental health in children with neurogenetic disorders associated with intellectual disability. Journal of the American Academy of Child & Adolescent Psychiatry, 59(9), 1036–1048. https://doi.org/10.1016/j.jaac.2020.01.006
  • Lichtenstein, P., Tideman, M., Sullivan, P. F., Serlachius, E., Larsson, H., Kuja‐Halkola, R., & Butwicka, A. (2022). Familial risk and heritability of intellectual disability: A population‐based cohort study in Sweden. Journal of Child Psychology and Psychiatry, 63(9), 1092–1102. https://doi.org/10.1111/jcpp.13560
  • Kendler, K. S. (2013). What psychiatric genetics has taught us about the nature of psychiatric illness and what is left to learn. Molecular Psychiatry, 18(10), 1058–1066. https://doi.org/10.1038/mp.2013.50

Co-occurring disorders

  • American Psychiatric Association. (2022). Diagnostic and Statistical Manual of Mental Disorders: Fifth Edition Text Revision DSM-5-TR. American Psychiatric Association Publishing, Washington, DC.
  • Buckley, N., Glasson, E. J., Chen, W., Epstein, A., Leonard, H., Skoss, R., Jacoby, P., Blackmore, A. M., Srinivasjois, R., Bourke, J., Sanders, R. J., & Downs, J. (2020). Prevalence estimates of mental health problems in children and adolescents with intellectual disability: A systematic review and meta-analysis. Australian & New Zealand Journal of Psychiatry, 54(10), 970–984. https://doi.org/10.1177/0004867420924101

Interventions

  • Ke, X., & Liu, J. (2020). Intellectual Disability. In J. M. Rey & A. Martin (Eds.), JM Rey’s IACAPAP Textbook of Child and Adolescent Mental Health (p. 25). International Association for Child and Adolescent Psychiatry and Allied Professions.
  • Sheerin, F., Eustace-Cook, J., Wuytack, F., & Doyle, C. (2021). Medication management in intellectual disability settings: A systematic review. Journal of Intellectual Disabilities, 25(2), 242–276. https://doi.org/10.1177/1744629519886184

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