Types of Mental Retardation

The different Types of mental retardness are :




Down's Syndrome (Mongolism)

The term mongolism has been used in referring to this syndrome because persons so afflicted frequently have almond-shaped slanting eyes. A number of physical features are often found among children with Down’s syndrome, but very few of these children have all of the characteristics commonly thought of as typifying this group. In addition to slanting eyes, the skin of the eyelids tends to be abnormally thick; the face and nose are often flat and broad, as is the back of the head; and the tongue, which seems too large for the mouth, may show deep fissures. The iris of the eye is frequently speckled. The neck is often short and broad, as are the hands, which tend to have creases across the palms. The fingers are stubby and the little finger is often more noticeable curved than the other fingers.

Mongoloids are particularly susceptible to circulatory, gastrointestinal, and respiratory disorders. However, antibiotics, better medical care, and a more healthful and stimulating environment are increasing the life expectancy of many of the victims of this disorder.

Research has shown that possible chromosomal anomalies lead to this disorder. Subsequent studies have shown that 95 percent of people with Down’s syndrome have 47 chromosomes instead of the normal component of 46 resulting from a trisomy of chromosome 21. (Normally chromosomes have no extra arm, but in this condition there is a presence of an extra arm on chromosome 21.)

The reason of trisomy of chromosome 21 is not clear, but the anomaly would appear to result from defective genes leading to some malfunction in the mechanics of the growth process. Trisomy of chromosome 21 is influenced by metabolic factors, but it is also possible that the older the mother, the greater the probability of exposure to radiation that may result in gene mutation.

There is no known effective treatment. When parents have had a child with Down’s syndrome, they are usually quite concerned about having further children. In such cases genetic counseling may provide some indication of the risk – which may be quite small – of abnormality in additional children.

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Phenylketonuria (PKU)
Phenylketonuria is a rare metabolic disorder. In PKU the baby appears normal at birth but lacks an enzyme needed to break down phenylalanine, an amino acid found in protein foods. When this condition is undetected, the phenylalanine builds up in the blood and leads to brain damage. The disorder usually becomes apparent between 6 and 12 months after birth, although such symptoms as vomiting, a peculiar odor, infantile eczema, (a skin disorder in infants), and seizures (fits) may become apparent during the early weeks of life. Often the first symptoms noticed are signs of mental retardation, which may be moderate to severe, depending on the degree to which the disease has progressed. Motor incoordination and other neurological manifestations relating to the severity of brain damage are also common, and often the eyes, skin, and hair of untreated PKU patients are very pale.

PKU is thought to result from metabolic alterations involving recessive genes, and 1 person in 70 is thought to be a carrier.

Methods for the early detection of PKU have been developed, and dietary and related treatment procedures are utilized. With early detection and treatment – preferably before an infant is 6 months old– the deterioration process can be arrested so that levels of intellectual functioning may range from borderline to normal functioning. However, a few children suffer mental retardation despite restricted phenylalanine intake and other treatment measures. For a baby to inherit PKU, both parents must carry the recessive gene. Thus when one child in a family has PKU, it is important that other children in such families be screened as well.

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Cretinism (Thyroid Deficiency)
Cretinism provides a dramatic illustration of mental retardation resulting from endocrine imbalance. In this condition, the thyroid either has failed to develop properly or has undergone degeneration or injury. In either case, the infant suffers from a deficiency in thyroid secretion. Brain damage resulting from this insufficiency is most marked during the prenatal and early postnatal periods of rapid growth.

Although most cases of cretinism result from lack of iodine in the diet, thyroid deficiency may also occur as the result of birth injuries (involving bleeding into the thyroid) or in connection with infectious diseases such as measles, whooping cough, or diphtheria. The resulting clinical picture will depend on the age at which the thyroid deficiency occurs, as well as on the degree and duration of the deficiency.

Typical descriptions of cretins involve cases in which there has been a severe thyroid deficiency from an early age, often even before birth. Such a cretin has a dwarflike, thick-set body and short, stubby extremities. His height is usually just a little over 3 feet, the shortness accentuated by slightly bent legs and a curvature of the spine. He walks with a shuffling gait that is easily recognizable. His head is large, with abundant black, wiry hair; his eyelids are thick, giving him a sleepy appearance; his skin is dry and thickened and cold on the touch. Other pronounced physical symptoms include a broad, flat nose, large and flappy ears, a protruding abdomen, and failure to mature sexually. The cretins reveal a bland personality, and his thought processes tend to be sluggish. Most cretins fall within the moderate and severe categories of mental retardation, depending on the extent of brain damage. In cases with less pronounced physical signs of cretinism, the degree of mental retardation is usually less severe.

Early treatment of cretinism with thyroid gland extract is considered essential, and infants not treated until after first year of life may have permanently impaired intelligence. In long–standing cases, thyroid treatment may have some ameliorating effects, but the damage to the individual’s nervous system and general physical development is beyond repair.

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Cranial Anomalies
Mental retardation is associated with a number of conditions in which there are relatively gross alterations in head size and shape, and where the causal factors have not been definitely established.

In macrocephaly ("large headedness"), for example there is an increase in the size and weight of the brain, an enlargement of the skull, and visual impairment, convulsions, and other neurological symptoms resulting from the supporting structure for brain tissue. Other cranial anomalies include microcephaly and hydrocephalus.

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The term microcephaly means "small headedness". It refers to a type of mental retardation resulting from impaired development of the brain and a consequent failure of the cranium to attain normal size. The most obvious characteristics of microcephalic is his small head, the circumference of which rarely exceeds 17 inches, as compared with normal of approximately 22 inches. Microcephalics differ considerably from each other in appearance, although there is a tendency for the skull to be coned shaped, with a receding chin and forehead. Microcephalics fall within the moderate, severe, and profound categories of mental retardation, but the majority shows little language development and is extremely limited in mental capacity.

Microcephaly may result from a wide range of factors that impair brain development, including intrauterine infections and pelvic irradiation of the mother during the early months of pregnancy. A number of cases of microcephaly that occurred in Hiroshima and Nagasaki apparently resulted from atomic bomb explosions during World War II. The role of genetic factors is not clear yet. The treatment is ineffective once faulty development has occurred, and, at present, preventive measures focus on the avoidance of infection and radiation during pregnancy.

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Hydrocephalus is a relatively rare condition in which the accumulation of an abnormal amount of cerebrospinal fluid within the cranium causes damage to the brain tissues and enlargement of the cranium.

In congenital cases of hydrocephalus, the head is either already enlarged at birth or begins to enlarge soon thereafter, presumably as a result of a disturbance in the formation, absorption, or circulation of the cerebrospinal fluid. The disorder can also develop in infancy or early childhood following the development of a brain tumor, subdural hemetoma,(clot in the brain covering), meningitis,(infection of brain covering) or other such conditions. Here the condition appears to result from a blockage of the cerebrospinal pathways and an accumulation of fluid in certain brain areas.

The clinical picture of hydrocephalus depends on the extent of neural damage, which, in turn, depends on the age at onset and the duration and severity of disorder. In chronic cases the chief symptom is the gradual enlargement of the upper part of the head out of all proportion to the face and the rest of the body. While the expansion of the skull helps minimize destructive pressure on the brain, serious brain damage occurs nonetheless, leading to intellectual impairment and such other effects as convulsions and impairment or loss of sight and hearing. The degree of intellectual impairment varies, being severe or profound in advanced cases.

A good deal of attention has been directed to the surgical treatment of hydrocephalus, and with early diagnosis and treatment this condition can usually be arrested before severe brain damage has occurred.

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