| Mental retardation (MR) is a common finding, affecting about 3% of the population. The most commonly used definition of mental retardation is a 'significant subaverage general intellectual functioning existing concurrently with deficits in adaptive behavior and manifested during the developmental period,' as stated by the American Association on Mental Deficiency. This can be translated as having an IQ below average (<70), causing problems communicating with others and learning the skills necessary for daily living and work and it is apparent before the age of 18.
Mental Retardation is usually classified by the child's IQ:
- mild: IQ of 55-69. About 85% of children with mental retardation are in this range and are further classified as being educable. These children may be able to learn to read and write at the 4th or 5th grade level, live relatively independently and work with special training.
- moderate: IQ of 40-54. Also described as being trainable. 10% of children with mental retardation are in this group. These children may have academic potential at the kindergarten or 1st grade level and may have limited ability to read, and will usually need some support and supervision in daily living activities (like with a supportive family or supervised group home) and work (with special training).
- severe: IQ of 25-39. 5% of children with mental retardation are in this group. Children with this level of mental retardation are unlikely to be able to learn to read or write, but may be able to be toilet trained and learn to dress with assistance. They usually require total supervision and support for daily living activities.
- profound: IQ of < 24. <1% of children with mental retardation are in this group.
A newer classification system was developed in 1992 that is based not on IQ scores, but rather on the amount of support and supervision that the individual needs: intermittent, limited, extensive and pervasive.
There are many different causes of why a child has mental retardation and they are usually grouped into prenatal, perinatal (around the time of birth) and postnatal causes. These include, but are not limited to:
- Prenatal causes
- chromosomal disorders, including Fragile X Syndrome
- gene defects
- exposure to toxins or infections during pregnancy
- Perinatal causes
- prematurity complications
- infection
- Postnatal causes
- infections
- lead poisoning or other toxins
- metabolic disorders
- head trauma
Up to half of children with mild mental retardation will have no cause that is identified, however children with severe mental retardation are much more likely (about 75%) to have a cause found. Testing to identify a cause for a child's mental retardation depends on which conditions are suspected and will very greatly from child to child. Testing may be limited to chromosomal analysis for Down Syndrome or Fragile X Syndrome, or more extensive testing may be done, including an MRI of the brain and metabolic screens for others. Testing will also include psychological tests to evaluate their IQ and level of functioning. Some common causes include:
- Down syndrome, the most common cause of moderate to severe mental retardation.
- Fragile X syndrome, the most common inherited cause of mental retardation.
- Rett syndrome, a progressive disorder that affects only females.
The symptoms of a child with mental retardation can vary greatly, depending on the cause and its severity. In general, most children without physical clues (such as infants with Down syndrome) are suspected of having mental retardation when they fail to meet age appropriate developmental milestones. Some children with mild mental retardation aren't identified until they begin school.
Treatments depend on the underlying cause, but in general, there is not a cure for mental retardation. Treatments are aimed at teaching skills necessary to maximize how independent they can be.
Children with mental retardation can have other conditions too, including autism, ADHD, anxiety disorders, depression, obcessive compulsive disorder, cerebral palsy, epilepsy, hyrocephalus, and spina bifida and they may have behavoiral problems. If present, these comorbid conditions should be treated too.
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