Mental retardation (MR), more commonly referred to as intellectual disability, is characterized by a person having significantly impaired cognitive functioning and deficits in two or more adaptive behaviors. This condition, which is diagnosed before the age of 18 and affects about 1 to 3 percent of the population, ultimately impairs the affected person’s ability to learn at an expected level and function normally in everyday life.
Usually, families begin to suspect something is wrong if the child’s motor, language and self-help skills do not appear to be developing or are developing at a much slower rate than the child’s peers. In more severe cases, these problems will show up early in a child’s life, while in mild cases, they may not appear until the child reaches school age or later.
There are two types of mental retardation: non-syndromic mental retardation and syndromic mental retardation. The former is the most common form of this condition—it affects up to 2 percent of children worldwide—and refers to children or adults with intelligent quotients (IQs) of less than 50 but have no physical abnormalities, while syndromic mental retardation refers to intellectual disability accompanied by other medical and behavioral signs and symptoms.
In addition, there is considerable variation in the severity of the condition. Some affected by this condition can live normal lives and require only minimal assistance, while others need 24-hour help. Experts use IQ scores to determine the severity of a child’s mental retardation. The normal IQ range is between 90 and 110. While a low IQ score isn’t the only determinant of mental retardation, a score below 70 is one of key elements of a diagnosis. (It is important to note that children with IQ scores between 70 and 89 are usually not thought to have an intellectual disability, but rather are seen as being below average.) Those with IQ scores ranging from 50/55 to 70 are said to have mild mental retardation; scores from 35/40 to 50/55 indicate moderate mental retardation; patients with scores from 20/25 to 35/40 are considered to have severe mental retardation; and those with scores below 20/25 have profound mental retardation.
There are many potential causes of mental retardation, but in about 70 to 75 percent of cases, doctors are unable to determine what caused a child’s intellectual disability. Possible causes include genetics, problems during pregnancy (e.g., infection or the mother using drugs or alcohol during pregnancy), exposure to diseases such as whooping cough or measles, and the baby not getting enough oxygen during delivery.