What Causes Mental Retardation?

Medically reviewed by Timothy J. Legg PhD, PMHNP-BC on April 20, 2016 Written by Shannon Johnson

If your child has an intellectual disability (ID), their brain doesn’t develop properly. Their brain may also not function within the normal range of both intellectual and adaptive functioning. In the past, medical professionals called this... Read More

If your child has an intellectual disability (ID), their brain doesn’t develop properly. Their brain may also not function within the normal range of both intellectual and adaptive functioning. In the past, medical professionals called this condition “mental retardation.”

There are four levels of ID: mild, moderate, severe, and profound. Sometimes ID may be classified as “other” or “unspecified.” ID involves both a low IQ and problems adjusting to everyday life. There may also be learning, speech, social, and physical disabilities.

Severe cases of ID are diagnosed at birth. However, you might not realize your child has a milder form of ID until they fail to meet common developmental goals. Almost all cases of ID are diagnosed by the time a child reaches 18 years of age.

Symptoms of intellectual disability

Symptoms of ID will vary based on your child’s level of disability and may include:

  • failure to meet intellectual standards
  • sitting, crawling, or walking later than other children
  • problems learning to talk or trouble speaking clearly
  • memory problems
  • inability to understand the consequences of actions
  • inability to think logically
  • childish behavior inconsistent with the child’s age
  • lack of curiosity
  • learning difficulties
  • IQ below 70
  • inability to lead a normal life due to challenges communicating, taking care of themselves, or interacting with others

If your child has ID, they will probably experience some of the following behavioral issues:

  • aggression
  • dependency
  • withdrawal from social activities
  • attention-seeking behavior
  • depression during adolescent and teen years
  • lack of impulse control
  • passivity
  • tendency toward self-injury
  • stubbornness
  • low self-esteem
  • low tolerance for frustration
  • psychotic disorders
  • difficulties paying attention

Some people with ID may also have specific physical characteristics. These can include having a short stature or facial abnormalities.

Levels of intellectual disability

ID is divided into four levels, based on your child’s IQ and degree of social adjustment.

Mild intellectual disability

Some of the following symptoms of mild intellectual disability include:

  • taking longer to learn to talk, but communicating well once they know how
  • being fully independent in self-care when they get older
  • having problems with reading and writing
  • social immaturity
  • inability to deal with the responsibilities of marriage or parenting
  • benefiting from specialized education plans
  • having an IQ range of 50 to 69

Moderate intellectual disability

If your child has moderate ID, they may exhibit some of the following symptoms:

  • are slow in understanding and using language
  • may have some difficulties with communication
  • can learn basic reading, writing, and counting skills
  • are generally unable to live alone
  • can often get around on their own to familiar places
  • can take part in various types of social activities
  • generally have an IQ range of 35 to 49

Severe intellectual disability

Symptoms of severe ID include:

  • noticeable motor impairment
  • severe damage to, or abnormal development of, their central nervous system
  • generally have an IQ range of 20 to 34

Profound intellectual disability

Symptoms of profound ID include:

  • inability to understand or comply with requests or instructions
  • possible immobility
  • incontinence
  • very basic nonverbal communication
  • inability to care for their own needs independently
  • the need of constant help and supervision
  • having an IQ of less than 20

Other intellectual disability

People in this category are often physically impaired, have hearing loss, are nonverbal, or have a physical disability. These factors may prevent your child’s doctor from conducting screening tests.

Unspecified intellectual disability

If your child has an unspecified ID, they will show symptoms of ID, but their doctor doesn’t have enough information to determine their level of disability.

What causes intellectual disability?

According to the Merck Manual, doctors can only identify a specific cause of ID in about a third of mild cases and two-thirds of moderate to profound cases.

Causes of ID can include:

  • trauma before birth, such as an infection or exposure to alcohol, drugs, or other toxins
  • trauma during birth, such as oxygen deprivation or premature delivery
  • inherited disorders, such as phenylketonuria (PKU) or Tay-Sachs disease
  • chromosome abnormalities, such as Down syndrome
  • lead or mercury poisoning
  • severe malnutrition or other dietary issues
  • early childhood illness, such as whooping cough, measles, or meningitis
  • severe brain injury

How is intellectual disability diagnosed?

To be diagnosed with ID, your child must have below average intellectual and adaptive skills. Your child’s doctor will perform a three-part evaluation:

  • interviews with you
  • observations of your child
  • standard tests

Your child will be given standard intelligence tests, such as the Stanford-Binet Intelligence Test. This will help the doctor determine your child’s IQ. The doctor may  also administer other tests such as the Vineland Adaptive Behavior Scales. This test provides an assessment of your child’s daily living skills and social abilities, compared to other children in the same age group.

It’s important to remember that children from different cultures and socioeconomic statuses may perform differently on these tests. To form a diagnosis, your child’s doctor will consider the test results, interviews with you, and observations of your child .

Your child’s evaluation process might include visits to specialists, who may include:

  • psychologist
  • speech pathologist
  • social worker
  • pediatric neurologist
  • developmental pediatrician
  • physical therapist

Laboratory and imaging tests may also be performed. These can help your child’s doctor detect metabolic and genetic disorders, as well as structural problems with your child’s brain.

Other conditions, such as hearing loss, learning disorders, neurological disorders, and emotional problems can also cause delayed development. Your child’s doctor should rule these conditions out before diagnosing your child with ID.

You, your child’s school, and your doctor will use the results of these tests and evaluations to develop a treatment and education plan for your child.

Treatment options for intellectual disability

Your child will probably need ongoing counseling to help them cope with their disability.

You will get a family service plan that describes your child’s needs. The plan will also detail the services that your child will need to help them with normal development. Your family needs will also be addressed in the plan.

When your child is ready to attend school, an Individualized Education Program (IEP) will be put in place to help them with their educational needs. All children with ID benefit from special education. The federal Individuals with Disabilities Act (IDEA) requires that public schools provide free and appropriate education to children with ID and other developmental disabilities.

The main goal of treatment is to help your child reach their full potential in terms of education, social skills, and life skills. Treatment may include behavior therapy, occupational therapy, counseling, and in some cases, medication.

What is the long-term outlook?

When ID occurs with other serious physical problems, your child may have a below average life expectancy. However, if your child has mild to moderate ID, they will probably have a fairly normal life expectancy.

When your child grows up, they may be able to work a job that requires basic intellectual skills. They may be able to live independently and support themselves. Support services are also available to help adults with ID live independent and fulfilling lives.

Medically reviewed by Timothy J. Legg PhD, PMHNP-BC on April 20, 2016 Written by Shannon Johnson

17 possible conditions

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This feature is for informational purposes only and should not be used to diagnose. Please consult a healthcare professional if you have health concerns.

Medically reviewed by Timothy J. Legg PhD, PMHNP-BC on April 20, 2016 Written by Shannon Johnson