Mental retardation (abbreviated as MR), is a term for a pattern of persistently slow learning of basic motor and language skills ("milestones") during childhood, and a significantly below-normal intellectual capacity as an adult.
During childhood, the term developmental delay is synonymous but currently preferred by some in most contexts because of the pejorative connotations acquired by the term "mental retardation". The American Association on Mental Retardation continues to use the term Mental retardation  (http://www.aamr.org/Policies/faq_mental_retardation.shtml).
Mental retardation is a concept and a condition similar to short stature:
- Diagnostic criteria are defined statistically and arbitrarily.
- There are many subgroups with distinguishable developmental patterns.
- It is not a single, homogeneous disease; there are many known causes, both inherent and environmental, and congenital and acquired.
- More than one factor may contribute to retardation for any one person.
- New conditions and causes are discovered or better understood each year.
- Treatments can be very effective, marginally beneficial, or ineffective, varying by cause and age of intervention.
- For a significant proportion of children, a cause cannot be determined.
A general, defined condition with various symptoms, caused by a lack of development of the brain before birth. These limitations will cause a child to learn and develop more slowly than a typical child. Children who have retardation may take longer to learn to speak, walk, and take care of their personal needs such as dressing or eating. They are likely to have trouble learning in school. They will learn, but it will take them longer. There may be some things they cannot learn.
There are three criteria before a person is considered to have mental retardation, their IQ is below 75, they have significant limits in two or more adaptive behavioral areas, and the condition is present since childhood. Down syndrome, fetal alcohol syndrome and fragile X are the three most common inborn causes of mental retardation.
Mental retardation is claimed to not be a disease. Mental retardation is also claimed to not be a type of mental illness, such as depression. There is no cure for mental retardation. However, with appropriate supports most individuals with retardation can learn to do many things.
Signs of Mental Retardation
There are many signs of mental retardation. For example, retarded children may:
- sit up, crawl, or walk later than other children;
- learn to talk later, or have trouble speaking,
- find it hard to remember things,
- not understand how to pay for things,
- have trouble understanding social rules,
- have trouble seeing the consequences of their actions,
- have trouble solving problems, and/or
- have trouble thinking logically.
About 87 percent of mentally retarded people will only be a little slower than average in learning new information and skills. When they are children, their limitations may not be obvious. They may not even be diagnosed as having mental retardation until they get to school. As they become adults, many people with retardation can live independently and may not be recognized by others in the community as having a disability.
The remaining 13 percent of individuals with mental retardation score below 50 on IQ tests. These people will have more difficulty in school, at home, and in the community. A person with more severe retardation will need more intensive support his or her entire life. Every retarded child is able to learn, develop, and grow. With help, all retarded children can live a satisfying life.
How is Mental Retardation Diagnosed?
Mental retardation is diagnosed by looking at two main things. These are:
- the ability of a person's brain to learn, think, solve problems, and make sense of the world (called IQ or intellectual functioning); and
- whether the person has the skills he or she needs to live independently (called adaptive behavior, or adaptive functioning).
Intellectual functioning, or IQ, is usually measured by a test called an IQ test. The average score is 100. People scoring below 70 to 75 are thought to have mental retardation. To measure adaptive behavior, professionals look at what a child can do in comparison to other children of his or her age. Certain skills are important to adaptive behavior. These are:
- daily living skills, such as getting dressed, going to the bathroom, and feeding one's self;
- communication skills, such as understanding what is said and being able to answer;
- social skills with peers, family members, adults, and others.
To diagnose mental retardation, professionals look at the person's mental abilities (IQ) and his or her adaptive skills.
Ranges of IQ
The following data based on the Wechsler Adult Intelligence Scale (WAIS) was used in 1958:
Today the following ranges are in standard use:
|Class ||IQ |
|Profound mental retardation ||below 20 |
|Severe mental retardation ||20-34 |
|Moderate mental retardation ||35-49 |
|Mild mental retardation ||50-69 |
|Borderline deficiency ||70-79 |
Causes of Mental Retardation
Doctors have found many causes of mental retardation. The most common are:
- Genetic conditions. Sometimes mental retardation is caused by abnormal genes inherited from parents, errors when genes combine, or other reasons. Examples of genetic conditions include Down syndrome, Fragile X syndrome, and phenylketonuria (PKU).
- Problems during pregnancy. Mental retardation can result when the baby does not develop inside the mother properly. For example, there may be a problem with the way the baby's cells divide as it grows. A woman who drinks alcohol (see fetal alcohol syndrome) or gets an infection like rubella during pregnancy may also have a baby with mental retardation.
- Problems at birth. If a baby has problems during labor and birth, such as not getting enough oxygen, he or she may have mental retardation.
- Health problems. Diseases like whooping cough, the measles, or meningitis can cause mental retardation. Mental retardation can also be caused by extreme malnutrition (not eating right), not getting enough medical care, or by being exposed to poisons like lead or mercury.
- Iodine deficiency is the leading, preventable cause of mental retardation in areas of the developing world where iodine deficiency is endemic.
The three traditional terms denoting varying degrees of mental deficiency long predate psychiatry. They were originally used in English as simple forms of abuse, and this is still the main usage. Their now obsolete use as psychiatric technical definitions is of purely historical interest. There have been some efforts made among mental health professionals to discourage use of these terms. Note that the term retard or tard is still used as a generic insult, especially among children.
- Idiot indicated the greatest degree of mental deficiency, where the mental age is 2 years or less, and the person cannot guard himself against common physical dangers. The term is gradually being replaced by the term profound mental retardation. The word is derived from the Greek ιδιωτης, idiŰtÍs, "a private citizen", from ιδιος, idios, "private". In ancient Athens, an "idiot" was a person who declined to take part in public life, such as democratic city government. This was considered irresponsible and so the term became one of derision.
- Imbecile indicated a mental deficiency less extreme than idiocy and not necessarily inherited. It is now usually subdivided into two categories, known as severe mental retardation and moderate mental retardation.
- Moron was defined by the American Association for the Study of the Feeble-Minded in 1910, following work by Henry H. Goddard, as the term for an adult with a mental age between eight and twelve; mild mental retardation is now the more widely-accepted term for this condition. Alternative definitions of these terms based on IQ were also used.
- Wechsler, David The Measurement of Adult Intelligence (1944), Baltimore, The Williams & Wilkins Company.
- Mental Deficiency Theories (http://faculty.ncwc.edu/toconnor/301/301lect04.htm) - from a criminology course, but provides a good overview
- Mental Retardation in Finland - Kehitysvammahuollon tietopankki (http://www.saunalahti.fi/kup/engl/finmr.htm)