Mental retardation is a developmental disorder characterized by a significantly below-average intelligence (an intelligence quotient [IQ] below 70) and an inability to function in and adapt to daily life without assistance. According to the Centers for Disease Control and Prevention (CDC), mental retardation affects about 12 out of every 1,000 schoolchildren in the United States, making it the most common developmental disorder.

Any brain injury or developmental problem in the brain may result in mental retardation. Such problems may occur before, during or after birth. Prenatal causes of mental retardation include genetic disorders (e.g., Down syndrome), infections in the mother or fetus during pregnancy (e.g., rubella, chickenpox) and exposure to various harmful substances (e.g., medications, alcohol, recreational drugs, radiation) during pregnancy. Serious infections in infancy (e.g., meningitis, measles) and serious head injuries (e.g., head trauma, shaken baby syndrome) in infants and children can also cause mental retardation. However, in many cases, the cause of mental retardation is not known.

Children with mental retardation tend to have trouble learning. They develop many skills and reach many developmental milestones at a later age than other children. These children may have trouble learning in school, especially difficulty solving problems or thinking logically.

Diagnosis of mental retardation relies on an evaluation of how well the patient thinks and functions. It includes standardized intelligence tests and an evaluation of how well the child functions in daily life. In general, the more severe the retardation, the earlier it is noticed. Mild cases may not be detected until the child begins school.

All children with mental retardation require an ever-changing educational and training program that is individualized especially for their abilities and needs. Young children with mental retardation may need assistance developing certain basic skills (e.g., motor skills, speech and language skills). Children with mental retardation require a special setting for education, including individual attention and support. However, those with mild retardation may be able to attend regular classes with other children their age with special assistance from a teacher or aide, both in and out of the classroom.

As a child with mental retardation enters adolescence, their education may focus more on developing independent living skills, such as work skills, using public transportation, social adaptation and managing money. Adolescents with mild retardation can usually look forward to living at least semi-independently once they reach adulthood. Those with more severe forms may require more direct care from a family member or other caretaker throughout their lives.

Many methods to prevent mental retardation begin before and during pregnancy. These include genetic counseling to evaluate a couple’s risk of having a child with mental retardation. It is also important to ensure that a woman is healthy both before and during pregnancy. When an infant is born, newborn screening tests are used to detect any conditions that need to be treated (e.g., phenylketonuria). After this point, mental retardation can often be avoided by avoiding brain injuries.

Mental retardation is a significantly below average intelligence combined with difficulty adapting and functioning in daily life. All patients with mental retardation require some degree of support. To be diagnosed with mental retardation, the condition must occur before adulthood (generally recognized as an age of 18 years).

Most cases of mental retardation are mild, and many people with mental retardation can live full, healthy lives. However, other physical problems may be present depending on the cause of the mental retardation. According to the Centers for Disease Control and Prevention (CDC), mental retardation is the number one long-term condition that causes major activity limitations in America.

Mental retardation is the most common developmental disorder, according to the CDC. It affects about 12 out of every 1,000 schoolchildren in the United States. It is more common in boys than in girls. There is wide variation in frequency of mental retardation from state to state. In general, it is more common in the southeastern states. This may be at least partially due to environmental and social and economic factors that are prevalent in this region.

The severity of mental retardation is most frequently measured by the patient’s intelligence quotient (IQ). The average IQ is 100 and “normal” intelligence ranges from an IQ of 90 to 110. People with an IQ of about 70 to 89 are considered below average, but not mentally retarded. The severity of mental retardation is divided into five categories:

• Mild retardation. IQ ranging from between 50 and 55 to about 70.
  
  
• Moderate retardation. IQ ranging from between 35 and 40 to between 50 and 55.
  
  
• Severe retardation. IQ ranging from between 20 and 25 to between 35 and 40.
  
  
• Profound retardation. IQ below 20 or 25.
  
  
• Unspecified. IQ cannot be tested, but is assumed to be low.

There is some overlap in IQ between each of these categories. When a patient’s IQ falls in this overlap, his or her level of functioning is used to determine severity. For example, a patient with an IQ of 52 and a higher level of functioning would be considered to have mild retardation. However, a patient with an IQ of 53 and a lower level of functioning would be considered to have moderate retardation.

In some cases, the severity of mental retardation is determined by how much and what kind of support is required. However, this can be vague and some physicians and scientists do not find it as useful as categorizing severity by IQ ranges.

Patients with mental retardation face numerous difficulties, including problems with communication, self-care skills, social situations and school activities. They tend to develop these and other skills more slowly than average.

Screening for developmental delays, including mental retardation, begins at birth. However, mental retardation is not usually diagnosed until much later, often when parents notice that a child is lagging behind peers or siblings. In general, the more severe the retardation, the earlier it is noticed. Mild cases may not be detected until the child begins school. The earlier mental retardation is identified, the better. If treatment and learning assistance begins early, levels of functioning can be increased and cognitive disabilities can be reduced.

All children with mental retardation require an ever-changing educational and training program that is individualized especially for their abilities and needs. These programs are guaranteed by the federal government through the Individuals with Disabilities Education Act (IDEA). This law regulates early intervention and special education services (provided by local schools) for all children with disabilities.

Young children with mental retardation may need assistance developing certain basic skills (e.g., motor skills, speech and language skills). These children are eligible for early intervention services, which may be available at little or no charge to parents. These services include an Individualized Family Services Plan (IFSP). This plan evaluates the unique needs and goals for each child and devises methods to address them.

Early intervention services frequently focus on adaptive skills. These are the skills that allow an individual to live, work and play in his or her community. They include communication skills, self-care skills (e.g., dressing, bathing, toilet training), health and safety lessons, home skills (e.g., making the bed, cleaning the bedroom, setting the table) and social skills (e.g., manners, rules of conversation, group structure and playing games).

Once children with mental retardation reach school-age, an Individualized Education Plan (IEP) replaces the IFSP. Like the IFSP, the IEP evaluates and addresses the unique needs and goals of a child. However, the plan is now more geared toward academics and school. Children with mental retardation require a special setting, including individual attention and support. However, many children with mild mental retardation may attend regular classes with other children their age, although they still require personal assistance from a teacher or aide, both in and out of the classroom. The education of children with mental retardation focuses on lifelong vocational pursuits. A particular interest or talent may be honed, with special vocational training or exposure to the job setting. For example, a child with an interest in cars may be educated with a strong focus towards machines and mechanics.

Children with mental retardation often can participate in many activities (e.g., sports, dance, music, art) with other children their age who do not have developmental disabilities. Their abilities to participate in these activities depend on their overall physical condition, including any condition that may have caused their mental retardation.

It is important that children with mental retardation are treated kindly and fairly. They may realize that they are behind other children their age in development and academics. In some cases, they may be bullied. Some of these children suffer from frustration or anxiety and some may act out in order to gain attention. Children with mental retardation need encouragement and support to prevent or overcome these potential obstacles.

Severe and profound mental retardation can lead to other problems. Children with such retardation may never learn adequate self-care or communication skills. There is some controversy as to whether these children are better suited to residential settings that include special education and extensive services or to community group homes and other smaller, more normal environments.

There are a number of steps parents, caretakers and teachers of children with mental retardation can take to help the child. It is important to encourage independence, including teaching adaptive skills whenever possible. The presentation of tasks and information needs to be concrete and clear. Breaking tasks and new information into smaller steps and facts and giving immediate feedback tends to help these children learn. Appropriate chores, with special attention to the child’s age, attention span and abilities, can make the child feel productive and independent. Socialization (e.g., scouts, recreational center activities, sports) can help build social skills and allow the child to have fun with other children of similar age. The child’s strengths and interests can be emphasized both in the classroom and at home.

As a child with mental retardation enters adolescence, his or her education may focus more on skills for independent living, such as work skills, using public transportation, social adaptation and managing money. The emphasis on individual strengths and interests and related vocations becomes even stronger at this point, making specialized vocational training a major goal.

Adolescents with mental retardation may become depressed. Depending on the severity of retardation, they may lack communication skills to express their feelings. This may result in other problems, such as eating or sleeping disorders. It is important to be attentive to these and similar problems and address them quickly.

Adolescents with mild retardation can usually look forward to living at least semi-independently once they reach adulthood. Those with more severe forms may require more direct care from a family member or other caretaker throughout their lives.

Hundreds of specific causes of mental retardation have been identified. Many of these are multiple congenital anomaly/mental retardation syndromes. These include any condition characterized by mental retardation as well as multiple birth defects. However, in nearly a quarter of all cases, the cause of mental retardation is not known.

Any brain injury or developmental problem in the brain may result in mental retardation. Such problems may occur before, during or after birth. Prenatal causes of mental retardation include genetic disorders (e.g., Down syndrome, Fragile X syndrome, phenylketonuria), infections in the mother or fetus during pregnancy (e.g., rubella, cytomegalovirus, chickenpox) and exposure to various teratogens during pregnancy. A teratogen is any chemical, substance or other harmful agent that may cause birth defects to a developing fetus. These include certain medications, alcohol, recreational drugs, smoking, and radiation. Prenatal conditions, especially chromosomal disorders or other genetic conditions, are by far the most common cause of mental retardation. Asphyxia (lack of oxygen to the brain) and other problems during delivery may also cause mental retardation. However, problems during delivery only rarely result in mental retardation.

Although the development of mental retardation in infancy or childhood is rare, it can occur due to several potential causes. Serious infections in infancy (e.g., meningitis, whooping cough, measles) and serious head injuries (e.g., shaken baby syndrome, head trauma) are important postnatal causes. Lead or mercury poisoning, suffocation, stroke and extreme malnutrition can also cause mental retardation. Infants who are born premature or with a low birthweight may also have an increased risk. There also seems to be an association between the age of the mother during the pregnancy and the risk of mental retardation in the child.

Most causes of mental retardation are present at birth (congenital). Some of these are major causes. Others are quite rare or only occasionally lead to mental retardation. Some of the major congenital conditions associated with mental retardation include:

• Down syndrome. A common genetic disorder that is among the most common causes of mental retardation. It is also characterized by slow growth and abnormal facial features. Heart defects are also common. Down syndrome is more common in children born to older mothers.
  
  
• Fragile X syndrome. A common genetic disorder that is a major cause of mental retardation in boys. It affects boys more frequently and more severely than girls. Other characteristics include shyness and social anxiety, learning disabilities, and autistic features (e.g., poor eye contact, odd movements).
  
  
• Fetal alcohol syndrome. A collection of birth defects and other problems caused by maternal alcohol consumption during pregnancy. Characterized by a low birthweight, abnormal facial features, behavioral problems and delayed development, including mental retardation.
  
  
• Cerebral palsy. A condition that causes brain damage and affects muscle control. The degree of impairment varies greatly among patients. Mental retardation and other neurological disorders (e.g., seizures) also occur in over half of all patients with the condition.
  
  
• Phenylketonuria. A metabolic abnormality in which protein is not properly processed and builds up in the bloodstream. It leads to mental retardation if left untreated, but early treatment with a special diet can be used to prevent brain damage.

Other conditions that often result in mental retardation, but are usually rare include:

• Miller-Dieker syndrome. A disorder characterized by an abnormally smooth brain surface (lissencephaly). This tends to result in severe mental retardation and other developmental problems, seizures and abnormal facial features.
  
  
• Rubinstein-Taybi syndrome. A genetic condition associated with moderate to severe mental retardation. Other characteristics include short stature, abnormal facial features, and broad thumbs and first (“big”) toes.
  
  
• Johanson-Blizzard syndrome. A rare genetic disorder that typically causes moderate mental retardation. However, some patients may have mild retardation or normal intelligence. Other characteristics include an abnormal nose that is small or “beak shaped,” tooth abnormalities, low birthweight and problems with digestion, the pancreas and the thyroid.
  
  
• Williams syndrome. A rare genetic condition associated with mild to moderate mental retardation and learning disorders. It is characterized by abnormal facial features that may be described as “elfin-like,” low muscle tone (hypotonia), loose joints, poor growth during infancy and early childhood, and heart and blood problems.
  
  
• Prader-Willie syndrome. A rare genetic disorder characterized by obesity due to constant, insatiable hunger. It is also associated with mental retardation and decreased muscle tone.
  
  
• Hunter syndrome. A rare metabolic disorder that only affects boys. It causes certain enzymes to build up and damage body tissues. It is characterized by abnormal facial features, mental retardation, hyperactivity, stiff joints, enlarged organs (e.g., liver, spleen) and hearing loss.
  
  
• Noonan syndrome. A genetic disorder that causes abnormal development. It is associated with abnormal facial features, mental retardation, short stature, delayed puberty and congenital heart disease.
  
  
• Thrombocytopenia absent radius (TAR) syndrome. A rare genetic disorder caused by low platelet levels (thrombocytopenia). It is characterized by potentially severe bleeding, which is worst during infancy. It often causes mental retardation, possibly due to bleeding in the brain. Other characteristics include underdevelopment or absence of the bones in the forearms, congenital heart disease and kidney defects.
  
  
• Dubowitz syndrome. A very rare genetic disorder with a wide range of signs and symptoms that may vary widely in severity between patients. Common signs and symptoms include mental retardation (usually mild), short stature, abnormal facial features, small head size and eczema.
  
  
• Ohdo blepharophimosis syndrome. A condition characterized by an inability to open the eye fully (blepharophimosis) and drooping eyelids. It is also associated with developmental delays, including mental retardation, tooth abnormalities, deafness, and congenital heart disease.
  
  
• Smith-Lemli-Opitz syndrome. A condition that occurs primarily in Caucasians. It is characterized by abnormal facial features, a small head size, mental retardation or learning disabilities, behavior problems, low muscle tone, and defects in the heart, lungs, kidneys, digestive tract and/or genitalia.
  
  
• Shprintzen syndrome. Also called velocardiofacial syndrome, this genetic condition is characterized by abnormalities in the back of the mouth and top of the throat, which cause speech problems. It is also associated with developmental delays, including mental retardation, congenital heart disease and abnormal facial features.

Other conditions that may occasionally result in mental retardation include:

• Adams-Oliver syndrome. A rare condition that affects the scalp and cranium. It is associated with limb abnormalities and, occasionally, mental retardation.
  
  
• Oculoauriculovertebral dysplasia. A rare genetic disorder with widely varying signs and symptoms that may occur in some patients but not in others. Some abnormalities in the cheeks, jaw, mouth, ears, eyes, and/or spinal column are usually present. They may occur on both or only one side of the body. Mild mental retardation may also be present.
  
  
• Weaver syndrome. Another condition characterized by rapid growth. It is associated with increased muscle tone (hypertonia), exaggerated reflexes (spasticity), foot deformities, and developmental delays, which may include mental retardation.
  
  
• Asymmetric crying facies syndrome. A condition caused by an underdeveloped facial muscle that causes the right and left side of the face to be misbalanced and look unmatched (asymmetry), particularly when smiling or crying. It is often associated with congenital heart disease.
  
  
• Beckwith-Wiedemann syndrome. A rare disorder that causes rapid growth. It is characterized by large body size, a large tongue, enlarged organs and kidney problems.
  
  
• Chondroectodermal dysplasia. Also called Ellis-van Creveld syndrome, this rare form of dwarfism is most common among the Pennsylvania Amish. It is characterized by short forearms and lower legs, extra fingers and toes (polydactyly), abnormal nails and teeth and heart defects.
  
  
• Pallister-Hall syndrome. A wide-ranging disorder than may be very mild and nearly unnoticeable or severe and life-threatening. When mild, it is associated with extra fingers or toes and bifid epiglottis (split in the tissue that blocks food from entering the windpipe). When severe, it is characterized by a split in the windpipe, resulting in death shortly after birth. More moderate forms may lie anywhere between these two extremes.

Children with mental retardation tend to have trouble learning and adapting to their environment. At very young ages, including infancy, they may seem to be in their own world (e.g., not interacting with the world around them). For example, they may not respond to their own reflections. They develop many skills and reach many developmental milestones at a later age than other children. For example, they often sit up, crawl, or walk at an older age, or develop social skills (e.g., understanding social rules and the consequences of their actions), self-care skills (e.g., dressing and eating without assistance) and speech and language skills later.

Children with mental retardation may have trouble learning in school (e.g., difficulty solving problems or thinking logically). In general, the more severe the mental retardation, the sooner these delays are apparent. Mild mental retardation may not be noticed until the child reaches school-age. In most cases, children with mental retardation have a greater delay in language skills than in other areas of development.

Some behavioral problems may occur in children with mental retardation. These include eating disorders, such as pica (desire to eat non-food items) and rumination (bringing up already swallowed food to re-chew), and self-stimulating movements (e.g., head-banging). These problems are less common in mild retardation and more common in more severe forms.

In some cases, prenatal tests (e.g., blood tests, ultrasound) may indicate whether a child may have a condition (e.g., a birth defect) that can cause mental retardation. For instance, ultrasound is among the most common prenatal tests. A fetal ultrasound can indicate whether a fetus may have Down syndrome.

Amniocentesis may also be performed to evaluate the likelihood of mental retardation. In amniocentesis, a needle is inserted into the uterus through the mother’s abdomen and a sample of amniotic fluid is extracted for testing. Chorionic villus sampling (CVS), which involves removing a sample of the placenta, may also be useful. Karyotypes (tests that allow a physician to evaluate the patient’s genetic structure) can be performed using both amniocentesis and CVS.

Diagnosing mental retardation after birth relies on an evaluation of how well the patient thinks and functions. A certified psychologist is typically required for an accurate diagnosis. This psychologist must be able to give, score and interpret standardized intelligence tests for the individual child and must be able to observe the child for how well he or she functions in daily life.

Several different standardized intelligence tests are available, with different tests appropriate for different ages. The Wechsler Intelligence Scales are the most commonly used intelligence tests for children older than 3 years. The Wechsler Scales include separate tests for children older and younger than 6 years, although a functional age is more important than a chronological age in this division.

This means that a child of 7 years who functions on a level closer to children of 5 years would be given the test directed towards the younger children. The Stanford-Binet Intelligence Scale may be used instead of the Wechsler Scales for school-aged children. Both of these scales focus on verbal skills. The Wechsler Scales also evaluates general performance skills, while the Stanford-Binet Scale evaluates thinking, memory and reasoning skills. The scores of different intelligence tests do not typically correlate with each other. In general, the tests for school-aged or older children are much more accurate than those for younger children.

While observing the child, the psychologist will be looking for self-care skills (e.g., toilet training, eating, dressing), communication skills and social skills. These skills may also be evaluated using a test called the Vineland Adaptive Behavior Scale. If the child is under the age of about 3-1/2 years, the Bayley Scales of Infant Development may be used.

Children who may have mental retardation also require a thorough examination, including a physical examination and an evaluation of their medical history. The medical history evaluation typically includes a thorough developmental history, including the progress of the pregnancy and delivery of the child. The child will also require periodic re-evaluations to monitor the condition. This allows any changes that may affect treatment to be noted.

Children with mental retardation are frequently tested for underlying conditions (e.g., Down syndrome, Fragile X syndrome) that may have caused their retardation. However, this is not always necessary or beneficial. Many causes of mental retardation are unknown, so many of these tests cause further financial and other burdens to the child’s family without providing any information. Physicians take many factors into consideration when deciding whether or not to perform these additional tests. These factors include the severity of the child’s mental retardation, whether or not the child appears to be at risk for a condition or a diagnosis seems likely, and parental concerns.

Testing is also more important if the child’s parents intend to have more children. If the mental retardation has a genetic cause, subsequent children may be at an increased risk of mental retardation as well.

Various tests may also be employed in an attempt to determine the cause of the mental retardation. This may include neuroimaging, blood tests and electroencephalograms (EEG). Karyotyping may be needed for children who may have a genetic disorder related to their chromosomes. If a condition that increases a child’s risk for mental retardation was noted during newborn screening tests, tests may be performed to ensure that it is still under control.

All children with mental retardation require a comprehensive evaluation to examine their own unique strengths, weaknesses and needs. This may require several different specialists, but typically includes a developmental pediatrician (a physician who specializes in child development).

Most cases of mental retardation are mild. These children can usually function at a near-normal level and, as adults, may be able to live independently. However, more severe cases require more constant support, often throughout life.

Children with mental retardation may require therapy and special training to learn many life-skills. This therapy may frequently be started before the child reaches school-age. It may include speech therapy (to improve communication skills), physical therapy (to improve motor skills) and special tutelage in other skills (e.g., social skills, work skills). Most children with mental retardation also require special schooling with an emphasis on individual attention and assistance.

A child’s pediatrician can help parents find local resources, such as early intervention agencies, support services and current literature and media. Local schools are another excellent source of information.

With comprehensive management, many children with mental retardation are able to vastly improve their levels of functioning. Sometimes, children with mild retardation no longer meet the criteria for retardation once they enter adulthood. Even children with more severe forms of mental retardation can greatly improve their ability to function. With time and training, their retardation may become less severe.

In many cases, mental retardation cannot be prevented. However, there are many steps both parents and children can take to help prevent mental retardation or reduce the child’s risk of developing it.

Many prevention methods begin before and during pregnancy. Genetic counseling can help evaluate a couple’s risk of having a child with a condition linked to mental retardation (e.g., Down syndrome). It is important for women to get any medical conditions under control and to get any needed vaccinations (e.g., rubella) several months before becoming pregnant. Certain blood tests can help evaluate a couple’s risk factors. For instance, blood tests can identify the likelihood of having a baby with Fragile X syndrome, a major cause of retardation.

While pregnant, a woman can reduce the risk of having a child with mental retardation by eating right, including plenty of calories and folic acid, and avoiding teratogens (harmful substances, such as alcohol or recreational drugs).

After a child is born, there are ways to help prevent the development of mental retardation. Newborn screening tests check for conditions that can cause mental retardation (e.g., phenylketonuria). If these conditions are treated early, mental retardation can often be prevented.

Another important step in the prevention of mental retardation is to prevent head injuries. Steps that can help prevent head injuries include:

• Never shake an infant. This may result in shaken baby syndrome, with can lead to mental retardation and infant death.
  
  
• Be careful to not drop an infant. Never leave an infant unattended on a changing table or other surface they could fall from. Any blow to the head could result in brain damage.
  
  
• Use car safety measures. Always use car seats, booster seats, or other child restraints, as appropriate for the child’s age, when in an automobile.
  
  
• Vaccinate children against common and serious infections, as directed by a pediatrician. Many infections can lead to mental retardation. However, there are now highly effective vaccinations for many of these.
  
  
• Protect children from falls. Children should be encouraged to use guard rails when using stairs and should not stand close to the edges of balconies, cliffs and other high places.
  
  
• Encourage children to wear helmets. All children should wear appropriate helmets when biking or skating. Certain sports (e.g., football, hockey) should only be played with appropriate helmets, as well.

Preparing questions in advance can help patients and parents have more meaningful discussions with physicians regarding their or their child’s treatment options. The following questions related to mental retardation may be helpful:

1. Why was my child’s mental retardation not detected earlier?
   
   
2. What may have caused my child’s mental retardation?
   
   
3. What can I expect from the condition that may have caused my child’s mental retardation?
   
   
4. How severe is my child’s mental retardation?
   
   
5. Where can I go to get information on early intervention and other services?
   
   
6. What type of schooling is most appropriate for my child?
   
   
7. What activities may my child participate in with other children his/her age?
   
   
8. What is the chance that my child will be able to function at least semi-independently as an adult?
   
   
9. Where can I go to meet and speak with other parents of children with mental retardation?
   
   
10. Since one of my children has mental retardation, how likely are my other children to develop it, too?