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What causes mental retardation? 17 possible conditions

Overview of Mental Retardation

Mental retardation or intellectual disability, (MR/ID), exists in children whose brains do not develop properly or function within the normal range. There are four levels of retardation: mild, moderate, severe, and profound. Sometimes, MR/ID may be classified as other or unspecified. Mental retardation involves both a low IQ and problems adjusting to everyday life.

MR/ID can result in learning, speech, physical, and social disabilities. Severe cases are diagnosed at birth. However, milder forms might not be noticed until a child fails to meet a common developmental goal. Almost all cases of MR/ID are diagnosed by the time a child reaches 18 years of age.

Levels of Mental Retardation

MR/ID is divided into four levels based on IQ and degree of social adjustment.

Mild Mental Retardation

At this level, a person:

  • takes longer to learn to talk, but can communicate well once he or she knows how
  • fully independent in self-care
  • has problems with reading and writing
  • is socially immature
  • is unable to deal with responsibilities of marriage or parenting
  • may benefit from specialized education plans
  • has an IQ range of 50 to 69
  • may have associated conditions, including autism, epilepsy, or physical disability

Moderate Mental Retardation

At this level, a person:

  • is slow in understanding and using language
  • has only a limited ability to communicate
  • can learn basic reading, writing, counting skills
  • is a slow learner
  • is unable to live alone
  • can get around on own
  • can take part in simple social activities
  • has an IQ range of 35 to 49

Severe Mental Retardation

At this level, a person:

  • has noticeable motor impairment
  • has severe damage to and/or abnormal development of central nervous system
  • has an IQ range of 20 to 34

Profound Mental Retardation

At this level, a person:

  • is unable to understand or comply with requests or instructions
  • is immobile
  • must wear adult diapers
  • uses very basic nonverbal communication
  • cannot care for own needs
  • requires constant help and supervision
  • has an IQ of less than 20

Other Mental Retardation

Children in this category are often blind, deaf, mute, and physically disabled. These factors prevent physicians from conducting screening tests.

Unspecified Mental Retardation

Signs of MR/ID exist, but there is not enough information to assign the child to a level.

What Causes Mental Retardation?

According to Psychology Today, only 25 percent of MR/ID cases have a known cause (Psychology Today, 2010).

When they are known, the cayses of mental retardation include:

  • trauma before or during birth, such as oxygen loss, alcohol exposure, or infection
  • genetic abnormalities, such as inherited abnormal genes, Down syndrome, fragile X syndrome, and PKU (phenylketonuria)
  • lead or mercury poisoning
  • severe malnutrition or other dietary issues
  • early childhood sickness, such as whooping cough, measles, or meningitis

Symptoms of Mental Retardation

Symptoms of MR/ID will vary based on the level of the disability. They can 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 beyond a normal age
  • lack of curiosity
  • learning difficulties
  • IQ below 70
  • inability to lead a normal life because of the inability to communicate, take care of oneself, or interact with others

Individuals who are intellectually disabled will often have 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
  • attention difficulties

Physical signs of MR/ID include short stature and malformed facial features. However, physical signs are not always present.

How Is Mental Retardation Diagnosed?

A diagnosis of MR/ID requires that both intellectual and adaptive skills be well below average. There are three parts to the evaluation:

  • interviews with parents
  • observations of the child
  • standard tests

Your child will be given standard intelligence tests, such as the Stanford-Binet Intelligence Test, to determine IQ. Other tests, such as the Vineland Adaptive Behavior Scales, will be given to assess your child’s daily living skills and social abilities compared with other children in the same age group. It is important to remember that children from different cultures and socio-economic statuses may perform differently on these tests. Results of these tests will be combined with information obtained from interviews with parents and observations of the child to assist in the diagnosis.

The screening process might include visits to many different professionals including the following:

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

Laboratory and imaging tests may be performed as well to detect metabolic and genetic disorders and structural problems with the brain. It is important to rule out such things as hearing loss, learning disorders, neurological disorders, and emotional problems as the cause for delayed development before making a diagnosis of MR/ID.

Once MR/ID has been diagnosed, the family, school, and primary care physician will use the results of these tests and evaluations to develop a treatment and education plan.

Treatment Options for Mental Retardation

Ongoing counseling will often be needed to help the child cope with disabilities.

Parents with intellectually disabled infants and toddlers will get a family service plan that describes their child’s needs. The plan will also detail the services the child will need to help him or her with normal development. Family needs are also addressed in the plan.

When the child is ready to attend school, a new plan, called the Individualized Education Program (IEP), will be put in place to assist the child with his or her educational needs.

The main goal of treatment is to assist the child in reaching his or her full potential in terms of education and social and life skills. Treatment may include behavior therapy, occupational therapy, counseling, and in some cases, medication. All children with MR/ID benefit from special education, and the federal Individuals with Disabilities Act (IDEA) requires that public schools provide free and appropriate education to children with mental retardation and other developmental disabilities.

What Is the Long-Term Outlook?

When MR/ID occurs with other serious physical problems, the life expectancy of the child may be shortened. In general, the more severe the cognitive disability and the more physical problems the child has, the shorter the life expectancy. However, a child with mild to moderate MR/ID has a fairly normal life expectancy. As adults, these people can often be successful at jobs that require basic intellectual skills, can live independently, and can support themselves.

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See a list of possible causes in order from the most common to the least.


Down Syndrome

Down syndrome is the most common genetic condition in the United States. It causes physical and mental developmental delays and disabilities.

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Hydrocephalus is a condition that occurs when fluid builds up in the skull and causes the brain to swell. The name literally means "water on the brain."

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Cerebral Palsy

Cerebral palsy is a disorder of muscle movement and coordination caused by an injury to a child's brain that occurs before birth or during infancy. It affects the part of the brain that controls body movement. Othe...

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Lead Poisoning

Lead poisoning occurs when lead builds up in the body. It is serious and sometimes fatal. Lead can be found in paint, art supplies, and other items. Poisoning may cause severe abdominal pain, seizures, and more.

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Fanconi Anemia

Fanconi anemia or FA is a genetic disorder that results in bone marrow failure. It is a recessive gene disorder. This means that in order for you to develop FA, your parents will both have to have the defective FA gene...

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Phenylketonuria is a rare genetic condition in which the body is unable to breakdown phenylalanine, an essential amino acid.

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Muscular Dystrophies

Muscular dystrophies are a group of inherited diseases that damage and weaken your muscles over time. This damage and weakness is due to the lack of a protein.

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Homocystinuria is an inherited disorder that keeps the body from processing the essential amino acid methionine. Amino acids are the building blocks of protein. Methionine occurs naturally in various proteins. It i...

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Tuberous Sclerosis

Tuberous sclerosis (TS) is a rare genetic condition. Sometimes called tuberous sclerosis complex (TSC), the disorder causes noncancerous (benign) tumors to grow in the brain and other vital organs, and on the skin...

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Ito Syndrome (Incontinentia Pigementi Achromians)

Ito syndrome (IS) is a rare condition characterized by loss of skin color on certain parts of the body. A serious abnormality associated with it is balding and missing or abnormally shaped teeth and nails.

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Genetic changes that occur while the fetus is growing can cause disorders that are present at birth. These are sometimes referred to as "congenital disorders." Acrodysostosis is one such condition, albeit a rare one...

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Huntington's Disease

Huntington's disease is a hereditary condition in which the brain's nerve cells gradually break down. This affects physical movements, emotions, and cognitive abilities. There is no cure, but there are ways to cope wit...

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Aarskog Syndrome

Aarskog syndrome is a very rare genetic disorder caused by a mutation on the X-chromosome that can affect a child's stature, facial features, genitalia, muscles, and bones. It primarily affects males.

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Aicardi Syndrome

Aicardi syndrome is a rare genetic disorder that interferes with the formation of the corpus collusum, the connector between two hemispheres of the brain. Medical researchers do not believe that the disorder is passe...

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Tay-Sachs Disease

Tay-Sachs is a disease of the central nervous system; it is a neurodegenerative disorder. Tay-Sachs most commonly affects infants. In infants, it is a progressive disease that is unfortunately always fatal. Rarely...

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As Rare as it Gets: Chediak Higashi Syndrome

Chediak-Higashi syndrome (CHS) is an extremely rare form of partial albinism that is accompanied by problems in the immune and nervous systems. Albinism is a lack of color in the skin, hair, and eyes. This specific typ...

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Basal Cell Nevus Syndrome

Basal cell nevus syndrome is a group of defects caused by a rare genetic condition that can cause tumors in the jaw.

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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.