People who are mentally handicapped have below average intellectual abilities and deficits in adaptive behavior. They tend to have impaired abilities to cope with routines and daily living skills. This disorder interferes with learning, communication, independence, motor ability, and social skills. Approximately one to three percent of the population is mentally handicapped.
The exact cause of the disability can only be identified in approximately fifty percent of those affected. Identified causes range from genetic disorders to trauma and toxins.
Genetic causes include single-gene defects, such as Fragile X syndrome. In 1992, Fragile X syndrome was identified as the most commonly inherited cause of mental handicaps. Chromosomal abnormalities, such as Down syndrome, translocations, and Klinefelter's syndrome, also cause impaired intellectual ability. Other genetic abnormalities cause metabolic disorders. These causes involve defective genes that are unable to produce the proteins or enzymes that are required for cells to function properly. More than 300 genetic metabolic disorders have been identified, including phenylketonuria (PKU), Tay-Sachs disease, and galactosemia. Congenital hypothyroidism can also cause mental handicaps.
Prenatal and postnatal trauma are also common causes, including intracranial hemorrhage, hypoxic injuries (often due to cerebral palsy), and head injuries. Certain infectious diseases can also lead to mental handicaps when they result in complications. Measles, chicken pox, and whooping cough may lead to encephalitis or meningitis, which can cause brain damage. Other infections, including congenital rubella, toxoplasmosis, and HIV can also lead to mental handicaps.
Non-inherited metabolic disorders, including Reye's syndrome, hypernatremic dehydration, and hypoglycemia may lead to mental disability. Exposure to toxins, such as lead and mercury, can cause brain damage, as can the mother's use of alcohol or drugs.
Nutritional problems during childhood, including Kwashiorkor, Marasmus and general malnutrition, can lead to mental disability. Poverty and lack of mental stimulation during infancy may also contribute to someone being mentally handicapped.
Mental handicaps are usually divided into four degrees of severity, based on IQ scores: mild (IQ range 55-70), moderate (IQ range 40-55), severe (IQ range 25-40), and profound (IQ below 25).
Mildly affected individuals make up the majority of the people who are mentally handicapped. They often cannot be distinguished from people of average intelligence in a social setting. They learn more slowly, and have difficulties with language, memory, and perception. They often have difficulty progressing beyond the academic skills associated with the sixth-grade level. As adults, they can lead fairly normal lives, working and living independently.
About ten percent of people with mental disabilities are moderately handicapped. They can acquire skills associated with the second-grade level, and by adolescence most can perform simple tasks, such as eating and dressing themselves. As adults, they can work at unskilled or semi-skilled jobs, but require support.
Severely handicapped individuals make up about three percent of those with mental disabilities. During adolescence or adulthood these individuals may learn to talk coherently and develop basic self-care skills. In adulthood, some can work at unskilled jobs with supervision. They often live in organized group homes or with their families.
About one percent of mentally disabled individuals are profoundly disabled. They can understand basic language, but usually cannot talk. Severe neurological conditions typically cause this level of disability.
Those affected by mental handicaps often show several characteristics in early childhood, often including:
- failure to achieve developmental or intellectual milestones
- infantile behavior persisting beyond normal expectations
- lack of curiosity
- difficulty speaking or understanding language
- lack of motor skill development
- inability to meet the educational demands of school
The primary goal for treating someone who is mentally handicapped is to develop the person's potential to its fullest. Special education programs often begin as early as infancy to help the child develop language and social skills, which are aimed at helping the person function as normally as possible as an adult.
Individuals who are mildly handicapped can develop new skills and abilities through early intervention and specialized education. Academically, many can function within a regular classroom if extra support is provided. More severely handicapped individuals require more support, and often require a segregated education program developed to meet their individual needs.
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