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Causes for Mental Retardation
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Mental Retardation Associated With Sociocultural Deprivation

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Mental Retardation Associated With Organic Causes








Mental Retardation Associated With Sociocultural Deprivation

Adverse sociocultural conditions, particularly those involving a deprivation of normal stimulation, may play a primary role in the etiology of mental retardation.
Two subtype of mental retardation can be    mental retardation associated with extreme sensory and social deprivation, such as prolonged isolation during the development years and cultural-familial retardation, in which the child is not subjected to extreme isolation but rather suffers from an inferior quality of interaction with his cultural environment and with other people.

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Cultural-familial mental retardation
Children who fall in this category are usually mild mental retardates; they make up the majority of persons labeled as mentally retarded and show no identifiable brain pathology. They are usually not diagnosed as mentally retarded until they enter school and have serious difficulties in their studies.

A number of studies point out that most of these children come from poverty-stricken, unstable, and often disrupted family backgrounds characterized by a lack of intellectual stimulation, an inferior quality of interaction with others, and general environmental deprivation.

Since a child’s current level of intellectual functioning is based largely on previous learning - and since schoolwork requires complex skills such as being able to control one's attention, follow instructions, and recognize the meaning of a considerable range of words - the child is at a disadvantage from the beginning if his environment has deprived him of the opportunity to learn requisite background skills and be motivated toward further learning. Thus with each succeeding year these children tend to fall farther behind in school performance and relative ratings on intelligence tests, unless remedial measures are undertaken. Many of these children do reveal a history of prematurity, inadequate diets, a little or no medical care.

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MENTAL RETARDATION ASSOCIATED WITH ORGANIC CAUSES

Genetic-Chromosomal Factors
Infections And Toxic Agents
Prematurity and Trauma ( Physical Injury)
Ionizing Radiation
Malnutrition and Other Biological Factors


Genetic-Chromosomal Factors
Mental retardation tends to run in families. This is particularly of mild retardation, which presumably is heavily influenced by the many genetic factors responsible for variations in intelligence. Genetic factors play a much clearer role in the etiology of relatively rare types of mental retardation such as Down's Syndrome. Here, specific genetic defects are responsible for metabolic alterations that adversely affect development of the brain. Genetic defects leading to metabolic alterations may, of course, involve many other developmental anomalies besides mental retardation. In general, mental retardation associated with known genetic-chromosomal defects is moderate to severe in degree.

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Infections and Toxic Agents
Mental retardation may be associated with a wide range of conditions due to infection. The fetus of a mother with certain virus diseases, such as German Measles, may suffer brain damage, as may the fetus of a mother with Syphilis. And, as in the case of viral encephalitis, brain damage may result from infections occurring after birth.

A number of toxic agents, such as carbon monoxide and lead, may also cause brain damage during fetal development or after birth. In some instances, immunological agents, such as antitetanus serum or typhoid vaccine, may lead to brain damage. Similarly certain drugs taken by the mother during pregnancy may lead to congenital malformations, or an overdose of drugs administered to the infant may result in toxicity and brain damage. In rare cases, brain damage results from incompatibility in blood types between mother and fetus – Rh or ABO system incompatibility. Fortunately, early diagnosis and blood transfusions can now minimize the effects of this disorder.

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Prematurity and Trauma ( Physical Injury)
Follow up studies of children born prematurely (weighing less than 1500 grams at birth) have revealed a high incidence of neurological disorders, including mental retardation. In fact, very small premature babies are about ten times more likely to be mentally retarded than normal infants.

Physical injury at birth can also result in retardation. Although normally the fetus is well protected by its fluid filled bag, and its skull appears designed to resist delivery stresses, accidents do happen during delivery, as well as after birth.

Difficulties in labor due to malposition of the fetus or other complications may irreparably damage the infant’s brain. Bleeding within the brain is probably the most common result of birth trauma. Anoxia – lack of sufficient oxygen to the brain stemming from delayed breathing or other causes – is another type of birth trauma that may damage the brain.

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Ionizing Radiation
In recent years a good deal of scientific attention has been focused on the damaging effects of ionizing radiation on sex cells and other bodily cells and tissues. Radiation may act directly on the fertilized ovum or may produce gene mutations in the sex cells of either or both parents, which, in turn, may lead to defective offspring.

Sources of harmful radiation were once limited primarily to high-energy X rays used for diagnosis and therapy, but the list has grown to include nuclear weapons testing and other radioactive materials to which people may be exposed.

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Malnutrition and Other Biological Factors
Deficiencies in proteins and other essential nutrients during early development can result in irreversible physical and mental damage. Protein deficiencies in the mother’s diet, as well as in the baby’s diet after the birth, have been pinpointed as particularly potent causes of lowered intelligence.

A limited number of cases of mental retardation are also associated with other biological agents, such as brain tumors that either damage the brain tissue directly or lead to increased cranial pressure and concomitant brain damage. In some instances of mental retardation – particularly of severe and profound types – the causes are uncertain or unknown, although extensive brain pathology is evident.

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