Intellectual disability begins in childhood. People with intellectual disability have limits in their mental functioning seen in below-average intelligence (IQ) tests and in their ability to communicate, socialize, and take care of their everyday needs. The degree of disability can vary from person to person. It can be categorized as mild, moderate, severe, or profound.
Several hundred causes of intellectual disability have been discovered, but many are still unknown. The most common ones are:
Biomedical causes resulting from:
- Abnormal genes inherited from parents
- Errors when genes combine, such as Down syndrome and Fragile X syndrome
- Nutritional deficiencies
- Metabolic conditions, such as phenylketonuria (PKU), galactosemia, and congenital hypothyroidism
- Developmental brain abnormality, such as hydrocephalus and brain malformation
Infections during pregnancy, such as:
- Herpes simplex
- Cytomegalovirus (CMV) infection
Behavioral issues during pregnancy, such as:
- Use of medications, drugs, or alcohol that affect the developing fetus
- Contraction of certain illnesses or infections while pregnant
Problems at birth, such as:
- Premature delivery or low birth weight
- Baby doesn’t get enough oxygen during birth
- Baby is injured during birth
Factors during childhood, such as:
- Nutritional deficiencies
- Illnesses or infections that affect the brain, including meningitis, encephalitis, chickenpox, whooping cough, and measles
- Exposure to lead, mercury, and other toxins
- Head injury or near drowning
- Social factors, such as child stimulation and adult responsiveness
- Educational deficiencies
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Symptoms appear before a child reaches age 18. Symptoms vary depending on the degree of the intellectual disability. If you think your child has any of these symptoms, do not assume it is due to intellectual disability. These symptoms may be caused by other, less serious health conditions.
- Learning and developing more slowly than other children of the same age
- Difficulty communicating or socializing with others
- Lower than average scores on IQ tests
- Trouble learning in school
- Inability to do everyday things like getting dressed or using the bathroom without help
- Difficulty hearing, seeing, walking, or talking
- Inability to think logically
The following categories are often used to describe the level of intellectual disability:
- IQ 50-70
- Slower than normal in all areas
- No unusual physical signs
- Can learn practical skills
- Reading and math skills up to grades 3-6
- Can conform socially
- Can learn daily task skills
- Functions in society
- IQ 35-49
- Noticeable delays, particularly speech
- May have unusual physical signs
- Can learn simple communication
- Can learn elementary health and safety skills
- Can participate in simple activities and self-care
- Can perform supervised tasks
- Can travel alone to familiar places
- IQ 20-34
- Significant delays in some areas; may walk late
- Little or no communication skills, but some understanding of speech with some response
- Can be taught daily routines and repetitive activities
- May be trained in simple self-care
- Needs direction and supervision socially
- IQ <20
- Significant delays in all areas
- Congenital abnormalities present
- Needs close supervision
- Requires attendant care
- May respond to regular physical and social activity
- Not capable of self-care
If you suspect your child is not developing skills on time, tell the doctor as soon as possible. You will be asked about your child’s symptoms and medical history. A physical exam will be done. Standardized tests may be given that measure:
- Intelligence—IQ tests measure a person’s ability to do things such as think abstractly, learn, and solve problems. A child may have intellectual disability if IQ test results are 70 or below.
Adaptive behavior—These are skills needed to function in everyday life, including:
- Conceptual skills like reading and writing
- Social skills like responsibility and self-esteem
- Practical skills like the ability to eat, use the bathroom, and get dressed
Children with intellectual disability have a higher risk for other disabilities such as hearing impairment, visual problems, seizures, attention deficit hyperactivity disorder, or orthopaedic conditions. Additional testing may be needed to check for other conditions.
Talk with your doctor about the best treatment plan for your child. Treatment is most helpful if it begins as early as possible. Treatment includes:
- Early intervention programming for infants and toddlers up to age 3
- Family counseling
- Human development training, including emotional skills and hand-eye coordination
- Special education programs
- Life skills training, such as preparing food and bathing
- Job coaching
- Social opportunities
- Housing services
To help reduce your child’s chance of becoming intellectually disabled, take the following steps:
- If you smoke, talk to your doctor about ways to quit.
- Don’t drink alcohol or use drugs.
- Eat a healthful diet—one that is low in saturated fat and rich in whole grains, fruits, and vegetables.
- Add extra folic acid to your diet.
- See your doctor regularly.
- Have your newborn screened for conditions that may produce intellectual disability.
- Have your child properly immunized.
- Schedule regular visits to the pediatrician.
- Use child safety seats and bicycle helmets.
- Remove lead-based paint from your home. Have your child tested for lead levels in the blood.
- Keep poisonous household products out of reach.
- Aspirin is not recommended for children or teens with a current or recent viral infection. This is because of the risk of Reye syndrome, which can cause neurological problems. Ask your doctor which medications are safe for your child.
This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.
Edits to original content made by Denver Health.
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a (Cognitive Disability; Developmental Disability; Mental Retardation)
Canadian Psychological Association http://www.cpa.ca
Special Olympics Canada http://www.specialolympics.ca
Causes and prevention of intellectual disabilities. The Arc website. Available at: http://www.thearc.org/page.aspx?pid=2453. Updated March 1, 2011. Accessed November 8, 2017.
Daily D, Ardinger H, et al. Identification and evaluation of mental retardation. Am Fam Physician. 2000;61(4):1059-1067.
Facts about intellectual disability. The Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/ncbddd/actearly/pdf/parents%5Fpdfs/IntellectualDisability.pdf. Accessed November 8, 2017.
Questions and answers about persons with intellectual disabilities in the workplace. US Equal Employment Opportunities Commission website. Available at: http://www.eeoc.gov/laws/types/intellectual%5Fdisabilities.cfm. Accessed November 8, 2017.