Mental Retardation
What is it?
Mental retardation is a developmental disability that can appear from birth through the age of 18. People who are mentally retarded function at an intellectual level that is below average and have difficulties with learning and daily living skills.Who gets it?
Approximately 2.5 to 3% of the total population are mentally retarded. In most cases, it is a lifelong condition. There is no connection between mental retardation and gender or race.What causes it?
In many cases, the cause of mental retardation is not found. About 5% of all cases can be linked to heredity. In these instances, the cause is a genetic defect, such as an inherited abnormal gene, gene mutation, or chromosomal defect. In very simple terms, genes are carried on thread-like structures called chromosomes, and determine our individual characteristics, such as how we look. Just one missing or faulty gene or chromosome can cause a birth defect. Two of the most common inherited causes of mental retardation are fragile X syndrome, caused by a defect in the chromosome that determines sex, and Down syndrome, caused by an extra chromosome. Gene defects such as phenylketonuria (PKU) can cause mental retardation if not found and treated early, as can hypothyroidism. Mental retardation can also occur as a result of the mother's behaviors or illnesses during pregnancy. Behaviors that can affect the fetus' developing brain include poor nutrition, excessive alcohol consumption, drug abuse, and cigarette smoking during pregnancy. Mental retardation due to alcohol abuse is called fetal alcohol syndrome. Pregnant women who have infections or illnesses such as rubella (German measles), cytomegalovirus, toxoplasmosis, glandular disorders, high blood pressure, or blood poisoning, or who are exposed to radiation during pregnancy, may have a mentally retarded child.Some birth defects that affect the head, brain, and central nervous system have mental retardation as a symptom. For example, neural tube defects, where the neural tube that forms the spinal cord does not close completely, can cause cerebrospinal fluid to accumulate on the brain. The pressure causes hydrocephalus, a cause of mental retardation. Difficulties in the birth process can also result in mental retardation. These include premature birth, head injury during birth, or lack of oxygen. Children can be born with normal intelligence but develop mental retardation because of childhood illnesses or injuries. Illnesses that cause mental retardation if not properly treated include chickenpox, measles, whooping cough, hyperthyroidism, or a bacterial infection called Hib disease. Meningitis and encephalitis can cause swelling in the brain that causes brain damage and mental retardation. Children who suffer a traumatic brain injury either accidentally or through abuse that includes violent blows to or shaking of the head may suffer brain damage and mental retardation.
Environmental factors that affect mental development include emotional and physical neglect. Daily stimulation is essential to a child's mental development. Infants who are neglected, as well as those who do not receive adequate nutrition, may suffer irreversible mental setbacks. Small children who live in older apartment buildings and homes painted with lead-based paint are at risk for developing lead poisoning if they put flakes of this paint into their mouths. Lead exposure can also cause mental retardation.
What are the symptoms?
The severity of symptoms of mental retardation and when they appear depend upon the cause. Symptoms appear during infancy if the condition is caused by a genetic disorder or an event during the pregnancy or birth process. A childhood illness or injury that causes a brain injury may suddenly make once easy tasks difficult for the child, and cause learning difficulties. In general, children who are mentally retarded fall behind when it comes to reaching developmental milestones. They may also show signs of aggression and self-injury. As they get older their scores on standardized intelligent quotient (IQ) tests are low and they have difficulties with daily life skills, called adaptive skills. Adaptive skills include basic communication, self-care, social, safety, and work skills. IQ levels are generally used to classify degrees of mental retardation. Children with mild retardation score in the range of 50 to 75. These children may not be diagnosed until they enter school because they develop social and communication skills during their first five years. However, learning difficulties become evident in a formal school setting. These children can learn up to the 6th grade level and can live independently with the support of family, community, and social services. Most children who are mentally retarded are in the mild category. About 10% of those with mental retardation are considered moderately retarded, with IQ scores in the range of 35 to 55. During early childhood, these children are able to learn to talk and communicate, but have poor social skills and awareness. Academically, they have difficulty working past the 2nd grade level. With supervision, they can learn some skills and take care of their personal needs. As these children reach adulthood, they can work well in a supervised setting, such as a group home. Children are classified as severely retarded when their IQ scores fall in the range of 20 to 40. This group accounts for only 3 to 4% of the mentally retarded population. The severely retarded have poor muscle coordination and limited communication and self-care skills during early childhood. By school age, they can learn some basic self-care and communication skills. These children benefit from living in a group home as they reach adulthood, and can perform some self-care under complete supervision.Profound retardation accounts for 1 to 2% of all mentally retarded people. With IQ scores of 20 to 25, these children have little muscle coordination during early childhood and do not reach developmental milestones, such as walking and talking. As they grow older, they may be able to perform some of the most basic self-care skills and may develop some speech skills. However, the profoundly retarded require skilled nursing care and constant supervision. Studies have shown that those with severe to profound mental retardation have a shortened life expectancy due to diseases that are often associated with these degrees of retardation. The American Association on Mental Retardation (AAMR) classifies degrees of mental retardation by the level of support the individual needs. These are intermittent support, limited support, extensive support, and pervasive (constant) support.
