Developmental Disability
A person is determined to have a developmental disability if at least one of the two following conditions exists:

Intellectual disability
This refers to significantly sub-average general intellectual functioning existing concurrently with deficits in adaptive behavior and manifested before the age of 18 years. Significantly sub-average is defined as an intelligence quotient (IQ) of 70 or below on standard measures of intelligence.

Related Condition
This is a severe, chronic disability that meets all of the following conditions:

It is attributable to-

• Cerebral palsy or epilepsy; or any other condition, other than mental illness, found to be closely related to an intellectual disability because this condition results in an impairment of general intellectual functioning or adaptive behavior similar to that of persons with intellectual disability, and requires treatment or services similar to those required for these persons.
• It is manifested before the individual reaches age 22.
• It is likely to continue indefinitely.
• It results in substantial functional limitations in three or more of the following areas of major life activity:
• Self-care (taking care of their own basic needs);
• Language (communicating with others);
• Learning (ability to learn new things);
• Mobility (getting from place to place);
• Self-direction (motivating and guiding themselves through daily living activities;
• Capacity for independent living (living independently including ability to earn enough money to live on).
• Children can be classified as having a developmental disability if it seems they will have these problems when they get older.

You may notice that some persons may have a diagnosis of cerebral palsy, epilepsy, or autism spectrum disorder and are not considered to be developmentally disabled. That's because if an individual has been diagnosed with cerebral palsy, epilepsy, or autism spectrum disorder, but not an intellectual disability and the disability is not considered to have created a substantial handicap, then it cannot be considered a developmental disability.

Intellectual disabilities are the most common of the developmental disabilities, but not everyone with a developmental disability has an intellectual disability. A developmental delay occurs when the child has not reached the milestones indicated for their age group. You can read more on this topic at
http://www.med.umich.edu/1Libr/yourchild/devmile.htm