is often poorly understood because its effects vary greatly among those who have it. Many people with intellectual disability are mildly affected and may not be identified until later during school years. Individuals with intellectual disability may also have physical or emotional problems.
People with intellectual disability who have a very low intelligence quotient (IQ) have serious limitations in their ability to function. However, with early intervention and appropriate support, they can also lead satisfying lives. The goal of treating intellectual disability is to help children stay in the family and participate in community life. In most states in the United States, they are guaranteed education and other services.
Intellectual disability begins in childhood and is characterized by limitations in both intelligence and adaptive skills. The following three criteria must be met for a diagnosis of intellectual disability:
IQ below 70
Significant limitations exist in two or more adaptive skill areas. These include:
CommunicationCommunity useFunctional academics (reading, writing, basic math)Health and safetyHome livingLeisureSelf-careSelf-directionSocial skillsWorkThe disability begins before age 18
Any condition that impairs development of the brain before birth, during birth, or during childhood can cause intellectual disability. The main causes can be categorized as follows:
Genetic abnormalities may be inherited from parents or may be caused by environmental factors.
There are many genetic diseases are associated with intellectual disability. Examples include:
—Children born with this rare genetic disorder cannot metabolize phenylalanine (PHE), which is an amino acid found in food. Without proper treatment, PKU can lead to intellectual disability.
—In a normal fertilized egg, chromosomes exist in pairs. But, in the case of Down syndrome, there are three of chromosome 21.
Fragile X syndrome
—This is caused by mutations of the FMR1 gene, the leading cause of inherited intellectual disability.
by a pregnant mother can cause intellectual disability.
can increase the risk, as well. Other risks during pregnancy include:
MalnutritionCertain environmental toxins (eg, lead)
Illnesses of a mother during pregnancy that can be passed on to her infant, such as:
(an infection caused by a parasite)
(caused by the herpes virus)
Prescription medicines (eg,
and low birth weight may sometimes lead to intellectual disability. These conditions may be associated with bleeding in or around the brain. However, other birth conditions or physical stress in the newborn stage may injure an infant's brain.
The American Association on Intellectual and Developmental Disabilities (AAIDD) has a process for diagnosing and classifying a person with intellectual disability. This process involves assessing the person's IQ and adaptive skills. Adaptive skills fall into three categories:
Conceptual skills—For example, can the person read and write? Does he understand concepts like time and money?Social skills—Does the person follow rules? Does he have interpersonal skills? Can he solve social problems?Practical skills—Can the person take care of his daily needs? Can he work, use money, and keep himself safe?
The best assistance for people with intellectual disability begins with diagnosis and help early in life. Treatment includes:
Case managementSpecial educationJob trainingHousing servicesTransition servicesFamily support (eg, respite care for caregivers)Early intervention
With enough education and support, many people with intellectual disability can learn to take care of their basic needs and to live in the community.
Newborn screening followed by proper treatment can prevent intellectual disability resulting from certain conditions. Examples include:
Phenylketonuria (PKU)Congenital hypothyroidism
Vaccines can prevent certain infectious diseases that may lead to intellectual disability. Women who plan to become pregnant should be current on all recommended vaccinations, such as:
Other interventions that can reduce the risk of intellectual disability include:
Early and comprehensive prenatal care, including prenatal vitamins containing folateAbstaining from alcohol, tobacco, and drugs during pregnancy
Many parents also choose to have certain tests done during pregnancy, including ultrasound, amniocentesis, chorionic villus sampling, and blood tests. These tests cannot prevent intellectual disability, but they can give parents more time to prepare for a child with intellectual disability.
Last reviewed August 2012 by Brian Randall, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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