Mental Retardation

Mental retardation is a condition marked by significantly lower intelligence than the average for individuals of the same age and by delays in developing social skills, communication skills, and the ability to care for oneself and live independently.

What Is Mental Retardation?

The definition of mental retardation changes as researchers study its causes and develop new ways of understanding its effects. Current definitions focus on intelligence levels and on the skills and behaviors for everyday living that people develop as they grow.

Intelligence

An intelligence quotient (IQ) is a test score that doctors and schools use to measure thinking, learning, and problem-solving skills. The IQ score for an average person always is set at 100. People who score above 120 are considered gifted. People who score below 80 are considered to have mental retardation. IQ scores define the severity of mental retardation using the following ranges:

• IQ 70-79: borderline
• IQ 55-69: mild
• IQ 40-54: moderate
• IQ 25-39: severe
• IQ below 25: profound.

A mentally retarded person is likely to be limited in most or all kinds of intelligence. The lower a person's IQ score, the more impaired his or her learning capacity is apt to be.

Adaptive behaviors

People with mental retardation are more limited than the average person in how well and how quickly they can learn to function in their environment. Limitations often involve language and communication, social skills, self-care, health and safety skills, leisure skills, the ability to live at home and/or in the community, and the ability to perform up to average standards in school or at work. This does not mean all people with mental retardation are unable to take care of themselves, however. Those with borderline mental retardation often are able to lead independent lives as adults if they receive extra support while they catch up to their peers in learning adaptive behaviors.

Mental illness

Mental retardation is not a mental illness. Sometimes people with mental retardation also have depression, anxiety, or other mental illnesses, just as people with average intelligence do. Oftentimes, though, they lead happy and healthy lives.

What Causes Mental Retardation?

Mental retardation sometimes has a genetic cause, resulting from one or more chromosomal abnormalities. Other times, though, mental retardation may be the result of problems during pregnancy that affect development of the fetal brain and central nervous system. Babies may be born with mental retardation if their mothers do not receive proper nutrition and medical care during pregnancy, if their mothers have infections during pregnancy or childbirth, or if their mothers are exposed to alcohol, drugs, or environmental toxins during pregnancy. Many different causes of mental retardation have been identified, but often a specific cause cannot be pinpointed for a specific individual.

Chromosomal abnormalities

Chromosomes are the threadlike structures in body cells that carry genetic information. Most cells in the human body have 23 pairs of chromosomes. Chromosome pair 23 determines whether a person is female (two X chromosomes) or male (one X chromosome and one Y chromosome) as well as other traits. Chromosomes 1 through 22 determine all our other traits and characteristics. Mental retardation may occur when a baby has an extra chromosome, an abnormal or partially missing chromosome, or a mislocated chromosome. The chromosomal abnormalities most often linked to mental retardation are Down syndrome and Fragile X.

Down syndrome

Down syndrome results from an abnormality on chromosome 21. People with Down syndrome may have three copies of this chromosome throughout the body (trisomy 21), or they may have three copies in some but not all cells (mosaic trisomy 21), or some of the genetic material from chromosome 21 may have become attached to a different chromosome (translocation trisomy 21). The physical differences that may result from chromosome 21 errors include mild to moderate mental retardation, a flat facial profile, an upward slant to the eyes, a short neck, a single deep crease on the palm, and increased risk of hearing loss, vision problems, thyroid disorders, and heart disease. Chromosome 21 errors have been linked to a mother's age. The incidence of Down syndrome in the children of mothers older than age 45 is 1 in 20, while for children of mothers younger than age 30 the incidence is less than 1 in 1,000.

Fragile X

Fragile X results from an abnormality on the X chromosome. It affects girls (XX) about twice as often as boys (XY), but symptoms are more severe in boys, because boys do not have a second X chromosome to help counter the effects of the defective one. The physical differences caused by Fragile X may include severe mental retardation, autism, a large head, protruding ears, a prominent jaw, and large testicles.

Metabolic disorders

Sometimes called "inborn errors of metabolism," these conditions result from abnormalities in the genes that govern how the body produces and handles amino acids, proteins, enzymes, hormones, and nutrients. One metabolic disorder that can cause mental retardation is phenylketonuria (FEN-il-KEE-toe-NOOR-ee-a), which is linked to a lack of the enzyme needed to process the amino acid phenylalanine (FEN-ill-AL-a-neen). Other such disorders include hypothyroidism (HY-poe-THY-royd-iz-um), linked to an underdeveloped, underactive, or damaged thyroid gland, which is needed to produce hormones essential for normal growth and brain development. Many metabolic disorders can be detected at birth by a blood test and treated through special diets, medications, and hormone therapy. If treatment is started early enough, mental retardation often can be prevented.

Brain development disorders

Problems that interfere with fetal development of the brain, spinal cord, and central nervous system may result in mental retardation, making proper prenatal medical care and good nutrition essential for pregnant women. Factors that are linked to brain development disorders include the mother's intake of folic acid (a B vitamin) and her exposure to teratogens (toxins), such as environmental waste, alcohol, tobacco, street drugs, and even some prescription medications. Brain development disorders include anencephaly ^* , hydrocephalus ^* , spina bifida ^* , autism, and fetal alcohol syndrome. Many people with either spina bifida or autism have brain development disorders but are not mentally retarded.

Fetal alcohol syndrome

When a pregnant woman drinks alcohol or takes drugs (legal or illegal), these substances are transmitted directly to the fetus. Mental retardation that is linked to a mother's drinking is known as fetal alcohol syndrome (FAS). In addition to mental retardation, children with FAS may have attention disorders, learning disabilities, skeletal problems, and distinctive facial characteristics, including widely spaced eyes, a shortened or flattened nose, and abnormalities in the shape and placement of the ears.

Infections

Serious infections can harm a baby's developing brain before birth or during early life. Viral infections linked to mental retardation include cytomegalovirus (SIE-toe-MEG-a-lo-VY-rus) and the rubella virus, which causes German measles. Encephalitis (en-SEF-uh-LIE-tis) and meningitis (MEN-in-JY-tis), two infections that involve inflammation of the brain, also can cause mental retardation.

Other causes

Other possible causes of mental retardation include premature or difficult birth, severe head injury, and lead poisoning. In many cases, however, doctors cannot identify specific causes, particularly when the mental retardation is mild. Because mental skills and intelligence are defined statistically by their distribution along a normal (bell) curve and by their variance from an average defined as 100, there always will be some individuals who are classified as intellectually gifted (IQ above 120) and others who are classified as mentally retarded (IQ below 80).

Diagnosing Mental Retardation

Chromosomal abnormalities and metabolic disorders often are diagnosed by doctors during prenatal testing or at birth. In other cases, however, a parent, caregiver, or teacher may be the first to notice that a baby or young child is not demonstrating new skills at the same pace as his or her peers. For example, the child may not crawl, walk, or talk by the expected age.

Using thorough physical and psychological examinations, doctors try to rule out other possible causes of the child's delays, such as hearing or vision problems, neuromuscular disorders, emotional or behavioral problems, learning or speech disorders, abuse, or a troubled home life. Pediatricians use blood tests, brain scans, genetic testing, and other medical tests to look for underlying physical disorders. Psychologists use developmental tests to help determine whether babies and children actually are behind peers, and they use standardized intelligence tests to compare the abilities of school-aged children to those of average children in the same age group. Psychologists also may observe the child at play, in school, and interacting with family members before making a diagnosis of mental retardation. Because developmental delays are not always linked to mental retardation, and because they may improve with physical treatment or changes in the child's environment, psychologists often schedule repeated evaluations over time to measure delays and assess improvements in intelligence and adaptive behaviors.

Living with Mental Retardation

Families

Parents who learn that an infant or child has mental retardation often are shocked, and they may be overwhelmed by feelings of sadness, helplessness, or anger until they adjust to the news. Family counselors and support groups often are needed to help parents learn how to meet the special needs of mentally retarded children and balance those needs with other family responsibilities, particularly to siblings who also must adjust to the situation. To help children with mental retardation, many families work with a team of specialists that includes psychologists, speech and language pathologists, physical and occupational therapists, social workers, and special education teachers.

Children

Children with mental retardation face many emotional challenges. They may know that they are "different" from their peers in ways that they may not understand. They may think that their families consider them a burden or an annoyance or a reason for shame, and they may be aware that they are "special needs" students in school. However, children with mental retardation can benefit from treatment and support in learning academic skills and the adaptive behaviors needed for everyday living. They also may get a boost in self-esteem by realizing that they, like other children, are unique and valuable individuals.

Adults

Adults with severe or profound mental retardation requiring constant supervision often enter nursing homes or other residential facilities that offer intensive 24-hour care. However, the majority of adults with mild to moderate mental retardation can achieve varying degrees of independence. Because they may want or need some support and guidance, many continue to live with family members or in group homes, apartment clusters, or hostels designed especially for people with special needs. Some are able to hold jobs and participate in community events such as the Special Olympics, which can help them develop greater self-esteem. Others are able to get married and start their own families.