Developmental Disabilities Definitions

Autism Spectrum Disorders (ASD), also known as Pervasive Developmental Disorders (PDDs), cause severe and pervasive impairment in thinking, feeling, language, and the ability to relate to others. These disorders are usually first diagnosed in early childhood and range from a severe form, called autistic disorder, through pervasive development disorder not otherwise specified (PDD-NOS), to a much milder form, Asperger syndrome. They also include two rare disorders, Rett syndrome and childhood disintegrative disorder.

Cerebral palsy refers to a group of disorders that affect a person's ability to move and to maintain balance and posture. It is due to a nonprogressive brain abnormality, which means that it does not get worse over time, though the exact symptoms can change over a person's lifetime. People with cerebral palsy have damage to the part of the brain that controls muscle tone. Muscle tone is the amount of resistance to movement in a muscle. It is what lets you keep your body in a certain posture or position.

Down syndrome is a genetic disorder that causes lifelong mental retardation, developmental delays and other problems. Down syndrome varies in severity, so developmental problems range from moderate to serious. Down syndrome is the most common genetic cause of severe learning disabilities in children, occurring in one in every 700 to 800 infants.

Epilepsy is a brain disorder in which clusters of nerve cells, or neurons, in the brain sometimes signal abnormally. In epilepsy, the normal pattern of neuronal activity becomes disturbed, causing strange sensations, emotions, and behavior or sometimes convulsions, muscle spasms, and loss of consciousness. Epilepsy is a disorder with many possible causes. Anything that disturbs the normal pattern of neuron activity - from illness to brain damage to abnormal brain development - can lead to seizures. Epilepsy may develop because of an abnormality in brain wiring, an imbalance of nerve signaling chemicals called neurotransmitters, or some combination of these factors. Having a seizure does not necessarily mean that a person has epilepsy. Only when a person has had two or more seizures is he or she considered to have epilepsy. EEGs and brain scans are common diagnostic test for epilepsy.

Fragile X syndrome is the most common form of inherited mental retardation. Fragile X happens when there is a change, or mutation, in a single gene called the Fragile X Mental Retardation 1 (FMR1) gene. This gene normally makes a protein the body needs for the brain to develop. But when there is a change in this gene, the body makes only a little bit or none of the protein, which can cause the symptoms of Fragile X.

Intellectual disability is characterized both by a significantly below-average score on a test of mental ability or intelligence and by limitations in the ability to function in areas of daily life, such as communication, self-care, and getting along in social situations and school activities. Intellectual disability is sometimes referred to as a cognitive disability or mental retardation. Children with an intellectual disability can and do learn new skills, but they develop more slowly than children with average intelligence and adaptive skills.