What Are Intellectual Disabilities?

According to the new definition by the American Association on Mental Retardation (AAMR), an individual is considered to have intellectual disabilities based on the following three criteria: intellectual functioning level (IQ) is below 70-75; significant limitations exist in two or more adaptive skill areas; and the condition manifests before the age of 18.

Adaptive skill areas are those daily living skills needed to live, work, and play in the community. The new definition includes 10 adaptive skills: communication, self-care, home living, social skills, leisure, health and safety, self-direction, functional academics, community use and work.

Adaptive skills are assessed in the person's typical environment across all aspects of an individual's life. A person with limits in intellectual functioning who does not have limits in adaptive skill areas may not be diagnosed as having an intellectual disability.

Children with intellectual disabilities grow into adults with intellectual disabilities; they do not remain "eternal children."

How prevalent are intellectual disabilities? The following statistics and information about intellectual disabilities have been adapted from information from the Population Reference Bureau, The Arc (formerly the Association for Retarded Citizens), the World Health Organization, and various associations for people with disabilities.

In the United States there are an estimated 7.5 million people with intellectual disabilities. This is approximately 2.5 to 3 percent of the U.S. population. Intellectual disabilities are 15 times more prevalent than cerebral palsy, 30 times more prevalent than neural tube defects such as spina bifida, 36 times more prevalent than total blindness, and 50 times more prevalent than total deafness.

According to the World Health Organization (1994), approximately 156 million people, or 3 percent of the world's population, have intellectual disabilities. Prevalence by continent: 20,310,000 in Africa, 525,000 in Australia, 97,710,000 in Asia, 15,390,000 in Europe, 13,800,000 in Latin America, and 8,610,000 in North America.

Intellectual disabilities knows no boundaries. It cuts across the lines of racial, ethnic, educational, social, and economical backgrounds. It can occur in any family. One out of 10 American families is directly affected by mental retardation.

Intellectual disabilities can be caused by any condition that impairs development of the brain before birth, during birth, or in childhood years. Several hundred causes have been discovered, but in one-third of the people affected the cause remains unknown. The three major causes of intellectual disabilities are Down syndrome, fetal alcohol syndrome, and fragile X syndrome. The causes can be categorized as follows:

Genetic conditions -- These result from abnormalities of genes inherited from parents, errors when genes combine, or from other disorders of the genes caused during pregnancy by infections, overexposure to X-rays, and other factors. Chromosomal abnormalities have also been related to some forms of intellectual disabilities such as Down syndrome and fragile X syndrome.

Problems during pregnancy -- Use of alcohol or drugs by pregnant mothers can cause intellectual disabilities. Fetal alcohol syndrome is the largest preventable cause of intellectual disabilities and is on the rise in the United States. The rate of children born with fetal alcohol syndrome has increased from 1 per 10,000 births in 1979 to 6.7 per 10,000 births in 1993. Malnutrition, rubella, glandular disorders and diabetes, and many other illnesses of the mother during pregnancy may result in a child being born with an intellectual disability. Physical malformations of the brain and HIV infection originating during prenatal life may also result in intellectual disabilities.

Problems at birth -- Although any birth condition of unusual stress may injure the infant's brain, prematurity and low birth weight predict serious problems more often than any other conditions.

Problems after birth -- Childhood diseases such as whooping cough, chicken pox, and measles can damage the brain, as can accidents such as a blow to the head or near drowning. Mercury and lead poisoning can cause irreparable damage to the brain and nervous system.

Poverty -- Children in poor families may become intellectually disabled because of malnutrition, disease-producing conditions, inadequate medical care, and environmental health hazards. Also, children in disadvantaged areas may be deprived of many common cultural and day-to-day experiences provided to other young children. Research suggests that such under-stimulation can result in irreversible damage and can serve as a cause of intellectual disabilities.

Can intellectual disabilities be prevented? During the past 30 years, significant advances in research have prevented many cases of intellectual disabilities. For example, every year in the U.S., we prevent; 250 cases of intellectual disabilities due to phenylketonuria (PKU) by newborn screening and dietary treatment; 1,000 cases of intellectual disabilities due to congenital hypothyroidism by newborn screening and thyroid hormone replacement therapy; 2,000 cases of intellectual disabilities or deafness by use of Rhogam to prevent Rh disease and severe jaundice in newborn infants; 3,000 cases of intellectual disabilities due to measles encephalitis through measles vaccination; and untold numbers of cases of intellectual disabilities caused by rubella during pregnancy through rubella vaccination. (Statistics from The Arc, 1993.)

New recommendations for worldwide treatment and prevention of intellectual disabilities and developmental disabilities are continuously being developed. Today, there are improved ways to manage head trauma, asphyxia (lack of oxygen), and infectious diseases such as polio and measles to reduce their adverse effects on the brain. Early intervention programs with high-risk infants and children have shown remarkable results in reducing the predicted incidence of subnormal intellectual functioning. Finally, early prenatal care and newborn screening programs have provided effective reductions in the incidence of intellectual disabilities. (The Arc, 1993.)