Causes And Diagnosis


What Causes Mental Retardation?

Doctors have found many causes of mental retardation. The most common are:

  • Genetic conditions. Sometimes mental retardation is caused by abnormal genes inherited from parents, errors when genes combine, or other reasons. Examples of genetic conditions are Down syndrome, fragile X syndrome, and phenylketonuria (PKU).
  • Problems during pregnancy. Mental retardation can result when the baby does not develop inside the mother properly. For example, there may be a problem with the way the baby's cells divide as it grows. A woman who drinks alcohol or gets an infection like rubella during pregnancy may also have a baby with mental retardation.
  • Problems at birth. If a baby has problems during labor and birth, such as not getting enough oxygen, he or she may have mental retardation.
  • Health problems. Diseases like whooping cough, the measles, or meningitis can cause mental retardation. Mental retardation can also be caused by extreme malnutrition (not eating right), not getting enough medical care, or by being exposed to poisons like lead or mercury.

Mental retardation is not a disease. You can't catch mental retardation from anyone. Mental retardation is also not a type of mental illness, like depression. There is no cure for mental retardation. However, most children with mental retardation can learn to do many things. It just takes them more time and effort than other children.

What Are The Signs Of Mental Retardation?

There are many signs of mental retardation. For example, children with mental retardation may:

  • sit up, crawl, or walk later than other children;
  • learn to talk later, or have trouble speaking,
  • find it hard to remember things,
  • not understand how to pay for things,
  • have trouble understanding social rules,
  • have trouble seeing the consequences of their actions,
  • have trouble solving problems, and/or
  • have trouble thinking logically.

About 87% of people with mental retardation will only be a little slower than average in learning new information and skills. When they are children, their limitations may not be obvious. They may not even be diagnosed as having mental retardation until they get to school. As they become adults, many people with mild retardation can live independently. Other people may not even consider them as having mental retardation.

The remaining 13% of people with mental retardation score below 50 on IQ tests. These people will have more difficulty in school, at home, and in the community. A person with more severe retardation will need more intensive support his or her entire life. Every child with mental retardation is able to learn, develop, and grow. With help, all children with mental retardation can live a satisfying life.

How Is Mental Retardation Diagnosed?

Mental retardation is diagnosed by looking at two main things. These are:

  • the ability of a person's brain to learn, think, solve problems, and make sense of the world (called IQ or intellectual functioning); and
  • whether the person has the skills he or she needs to live independently (called adaptive behavior, or adaptive functioning).

Intellectual functioning, or IQ, is usually measured by a test called an IQ test. The average score is 100. People scoring below 70 to 75 are thought to have mental retardation. To measure adaptive behavior, professionals look at what a child can do in comparison to other children of his or her age. Certain skills are important to adaptive behavior. These are:

  • Daily living skills, such as getting dressed, going to the bathroom, and feeding one's self;
  • Communication skills, such as understanding what is said and being able to answer;
  • social skills with peers, family members, adults, and others.

To diagnose mental retardation, professionals look at the person's mental abilities (IQ) and his or her adaptive skills. Both of these are highlighted in the definition of mental retardation provided between the lines below. This definition comes from the Individuals with Disabilities Education Act (IDEA). The IDEA is the federal law that guides how schools provide early intervention and special education and related services to children with disabilities.

Providing services to help individuals with mental retardation has led to a new understanding of how we define mental retardation. After the initial diagnosis of mental retardation is made, we look at a person's strengths and weaknesses. We also look at how much support or help the person needs to get along at home, in school, and in the community. This approach gives a realistic picture of each individual. It also recognizes that the "picture" can change. As the person grows and learns, his or her ability to get along in the world grows as well.


Sourced from: Mental Retardation Fact Sheet (FS8)
National Dissemination Center for Children with Disabilities
Revision: January 2004