Mental retardation is a condition mainly found in children, which is quantified by two factors:

Mild mental retardation is indicated by an IQ of 52-68, moderate retardation by an IQ of 36-51, severe retardation by an IQ of 20-35 and profound retardation by an IQ of 19 or below.

The mildly retarded are able to learn how to speak, interact socially, walk, write and can be educated up to a sixth grade level by their late teens. They are usually able to work and conform to societal standards, but may need assistance in times of stress.

The moderately retardated are able to talk or communicate, but are relatively socially unaware. Education beyond the equivalent of the second grade is unlikely, and they may be able to do unskilled work.

The severely retarded can only learn a very small number of words, have very few, or no modes of expression and have very poor muscle coordination. They are able to learn a very limited set of self-help skills in a controlled environment.

The profoundly retarded have very poor muscle coordination, little to no ability to care for themselves and almost always need nursing care.


Mental retardation is below average mental ability usually present from birth or early childhood.  Those who suffer from  mental retardation usually have lower mental development than normal people, and learning difficulties along with problems adapting socially.  About 4% of the total population suffered from mental retardedation.


A persons intelligence level is determined by their heredity and the environment in which they live.  In many cases the cause is a mystery.  But, conditions during  pregnancy can cause or contribute to mental retardation in the newborn child.  Conditions that contribute may include lack of proper nutrition, the use of certain medications, radiation treatment, alcohol abuse, and some viral infections. Diseases such as Down's Syndrome, can be a cause of mental retardation.  A number of genetic disorders may also cause mental retardation.  Some, such as low thyroid levels, can be properly treated before mental retardation happens.  Premature birth difficulties, injuries to the head during the birth process, and extremely low oxygen levels during the birth process may also cause mental retardation.

Diagnosis and Prognosis

Once mental retardation has occurred, it is usually irreversible.  Diagnosing mental retardation early makes remedial education and long-term planning possible.

Subaverage intelligence can be identified and measured by standardized intelligence tests.  Such tests have a middle-class bias but are reasonably accurate predictors of intellectual performance, particularly in an older child.

Children with and IQ of 69 to 84 have difficulty in school learning but are not mentally retarded.  They are rarely identified before beginning school, when educational and sometimes behavioral problems become evident.  With special educational help, they can usually succeed in school and lead normal lives.

All children with mental retardation can benefit from education.  Children with mild retardation may attain fourth to sixth grade reading skills.  Although they have difficulty reading, most mildly retarded children can learn the basic educational skills needed for everyday life.  They require some supervision and support and special educational and training facilities.  They may later require a sheltered living and work situation.  Though usually free or obvious physical defects, people who are mildly retarded may have epilepsy.

The mildly retarded are often immature and unsophisticated, with a poorly developed capacity for social interaction.  Their thinking is concrete and they are often unable to generalize.  They have difficulty adjusting to new situations and may demonstrate poor judgment, lack of foresight, and gullibility.  Although they don't commonly commit serious offenses, the mildly retarded may commit impulsive crimes, often as members of a group and sometimes to achieve peer group status.

Children with moderate retardation are obviously slow in learning to speak and reaching other developmental milestones, such as sitting up and speaking.  Given adequate training and support, mildly and moderately retarded adults can live with varying degrees of independence within the community.  Some can cope with just a little support in a halfway house, whereas others need greater supervision.

The severely retarded child is trainable to a lesser degree than a child who is moderately retarded.  The profoundly retarded child usually can't learn to walk, talk or understand very much.

The life expectancy of children with mental retardation may be shortened, depending on the cause and severity.  In general, the more severe the retardation, the shorter the life expectancy.


Genetic counseling gives parents of a child with retardation knowledge and understanding of the cause of retardation.  Counseling helps them assess the risk of having another child who is retarded.  Amniocentesis and chorionic villus sampling are diagnostic tests that can detect a number of abnormalities, including genetic abnormalities and spinal cord or brain defects in the fetus.  Amniocentesis or chorionic villus sampling is advisable for all pregnant women over 35 years old because of their increased risk of having a baby with Down's Syndrome.  Ultrasound examination may also identify fetal brain defects.  The serum alpha-fetoprotein level in the mother's blood can be measured to screen for Down's Syndrome and Spina Bifida.  The rubella vaccine has dramatically decreased German measles as a cause of mental retardation.


The primary care doctor, in consultation with a number of specialists, develops a comprehensive, individualized program for the child with retardation.  A child with developmental delays should be started in an early intervention program as soon as the diagnosis of mental retardation is suspected.  Emotional support of the family is an integral part of the program.  A child with retardation usually does best living at home or at a community-based residence and, if possible, attending a normal day care center or preschool program.

The level of social competence is as important as the IQ in determining how limiting the retardation will be.  The IQ and social competence are both problems for children at the lower end of the IQ scale.  For children with higher IQ scores, other factors, such as physical handicaps, personality problem, mental illness, and social skills, can determine how much care is needed.

Source:  Margolis, Simeon, The Johns Hopkins Medical Handbook, 2001

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