What is Developmental Disability?

Developmental Disability is a disorder in which a person's intellectual functioning is well below the average 90-110 intelligence quotient (IQ). A person has developmental disability when intellectual functioning level (IQ) is below 69; there is significant limitations in at least two adaptive skill areas; and the condition has existed since childhood. There are varying degrees of developmental disability. Mental health clinicians have defined four degrees of severity based on IQ score: mild, moderate, severe, and profound.

Facts Developmental disability appears in childhood, before age 18. Over 7 million Americans have developmental disability. One out of every 10 American families is directly affected by developmental disability. Developmental disability occurs in people of all racial, ethnic, education, and economic backgrounds.

Mild (IQ range 50-55 to 69) - More than 85% of those with developmental disability are mildly affected. They often cannot be distinguished from normal children until in school. Although they learn more slowly, people with mild developmental disability usually can develop academic skills equivalent to the 6th-grade level. As adults, they can lead satisfying lives in the community with minimal assistance.

Moderate (IQ range 35-40 to 50-55) - About 10% of people with developmental disability are moderately disabled. They can progress to about the second-grade level in academic skills. By adolescence, they usually have good self-care skills and can perform simple tasks. As adults, most can work at unskilled or semiskilled jobs with supervision.

Severe (IQ range 20-25 to 35-40) - Severe disability affects 3-4% of developmentally disabled individuals. Severely disabled individuals may learn to talk during childhood and develop basic self-care skills. In adulthood they can perform routine tasks with close supervision. They often live in group homes or with their families.

Profound (IQ level below 20-25) - About 1-2% percent of developmentally disabled people have profound developmental disability and require constant care. Profoundly disabled individuals can understand some language and may have some adaptive communication skills (e.g.: gesturing, pointing, etc.) but they have little ability to talk. They often have a neurological condition that accounts for their disability.

What Causes Developmental Disability?

Developmental disability can be caused by any condition that impairs development of the brain. It can occur before birth while a fetus develops, during birth or during childhood. Scientists can identify a specific cause in 60 to 70 percent of developmental disability cases. Some cases of developmental disability have multiple causes.

Leading Causes

Before Birth

• Fragile X syndrome, the leading cause of inherited developmental disability, is a chromosomal disorder resulting in a weak spot located on the X chromosome which is susceptible to breaking.

• Down syndrome occurs when there is all or part of an extra copy of a pair of chromosomes known together as chromosome 21.

• Fetal alcohol syndrome, the most common cause of preventable developmental disability in the US, results from excessive consumption of alcohol during pregnancy.

During Birth

Some cases of developmental disability result from problems during birth, including premature birth, very low birth weight, and stresses to the baby such as deprivation of oxygen.

During Childhood