What is a Developmental Disability?

A developmental disability is a severe long-term problem that may be physical or affect mental ability. Developmental disabilities are attributable to intellectual disability (formerly known as mental retardation), cerebral palsy, epilepsy, autism, or disabling conditions found to be closely related to intellectual disability. In order to be considered a developmental disability, the disability must originate before eighteen years of age, be likely to continue indefinitely, and constitute a substantial disability for the individual.

A substantial disability is a condition which results in major impairment of cognitive and/or social functioning. Such limitations include receptive and expressive language, learning, self-care, mobility, self-direction, capacity for independent living, and economic self-sufficiency.

The following are descriptions and characterizations of individuals with the aforementioned disabling conditions. However, it should be understood that all persons are individuals and should not be limited by such descriptions. Talents and abilities should be assessed on an individual basis and training, education, and support should be customized to work with an individual’s strengths and promote continued learning, regardless of the diagnosis or generalized characteristics of the disability.

Intellectual Disability (ID)

Intellectual Disability refers to substantial limitation in present functioning. It is characterized by significantly sub-average intellectual functioning, existing concurrently with related limitations in two or more of the following adaptive skill areas: communication, self-care, home living, social skills, community use, self-direction, health and safety, functional academics, leisure or work.

There are four degrees of severity specified, reflecting the level of intellectual impairment which include Mild, Moderate, Severe, and Profound. These classifications are based on a combination of IQ levels and demonstrated functional capabilities. The IQ level classifications are as follows:

Independent living assists residents with daily life skills.
Independent living assists residents with daily life skills.
Job coach assists a Clausen House client with finding a new job.
Job coach assists a Clausen House client with finding a new job.

Mild Intellectual Disability

This group constitutes the largest segment (about 85%) of those with the disorder. As a group, people with this level of Intellectual Disability typically develop social and communications skills during the preschool years (ages 0-5 years), have minimal impairment and sensorimotor areas, and often are not distinguishable from persons without Intellectual Disability until a later age. By their late teens, they can acquire academic skills up to approximately the sixth-grade level. During their adult years, they usually achieve social and vocational skills adequate for minimum self-support, but may need supervision, guidance, and assistance, especially when under unusual social or economic stress. With appropriate support, individuals with Mild Intellectual Disabilities can usually live successfully in the community, either independently or in supervised settings.

Severe Intellectual Disability

The group with Severe Intellectual Disability constitutes 3% to 4% of individuals with Intellectual Disability. During early childhood years, they acquire little or no communicative speech. During the school-age period, they may learn to talk and can be trained in elementary self-care skills. They profit to only a limited extent from instruction in pre-academic subjects, such as familiarity with the alphabet and simple counting, but can master skills such as learning sight reading of some “survival” words. In their adult years, they may be able to perform simple tasks in closely supervised settings. Most adapt well to life in the community, in group homes, or with their families unless they have an associated handicap that requires specialized nursing or other care.

Moderate Intellectual Disability

This group constitutes about 10% of the entire population of people with Intellectual Disability. Most of the individuals with this level of Intellectual Disability acquire communication skills during early childhood years. They rather profit from vocational training and, with moderate supervision, can attend to their personal care. They can also benefit from training in social and occupational skills but are unlikely to progress beyond the second-grade level in academic subjects. They may learn to travel independently in familiar places. During adolescence, their difficulties in recognizing social conventions may interfere with peer relationships. In their adult years, the majority are able to perform unskilled or semiskilled work under supervision in sheltered workshops or in the general workforce. They adapt well to life in the community, usually in supervised settings.

Profound Intellectual Disability

The group with Profound Intellectual Disability constitutes approximately 1% to 2% of people with Intellectual Disability. Most individuals with this diagnosis have an identified neurological condition that accounts for their Intellectual Disability. During the childhood years they display considerable impairments in sensorimotor functioning. Optimal development may occur in a highly structured environment with constant aid and supervision and an individualized relationship with a caregiver. Motor development and self-care and communication skills may improve if appropriate training is provided. Some can perform simple tasks in closely supervised and sheltered settings.

Cerebral Palsy

Cerebral Palsy is a non-progressive disorder of voluntary movement or posture that is caused by a malfunctioning of, or damage to, the brain occurring before birth, during birth, or within the first few years of life. Individuals with Cerebral Palsy may or may not have a concurrent intellectual disability, meaning that many individuals with Cerebral Palsy are only affected by impairment to movement and function cognitively in the normal range. Others may also be impaired cognitively.

Early treatment intervention for the movement disorder of Cerebral Palsy may include development of normal postural reactions and postural tone against gravity for support and control of movement; counteracting the development of abnormal postural tone; giving the child, by means of handling and play, functional patterns that later will be used for feeding, dressing, washing, and other self-help activities; and to prevent the development of contractures and deformities.

Ongoing treatment will continue to focus on the aforementioned areas and include physical therapy treatment techniques to address physical aspects of the condition, occupational therapy to address training of activities of daily living, and surgical measures to address physical mobility.


Epilepsy refers to a wide variety of seizure conditions which oftentimes, depending on the type of seizure, result in physical convulsions of the body. A seizure involves a disruption of the normal activity of the brain through neuronal instability, firing in an abnormally rapid manner. This excessive electrical discharge results in a seizure. The extent to which seizures affect brain functioning depends on both the duration and location within the brain. Consequently, some seizures impair brain functioning slightly, while other seizures result in complete cessation of normal activities. There are two major types of seizures:

  • Generalized seizures that affect both cerebral hemispheres.
  • Partial (focal) seizures that affect a specific part of one cerebral hemisphere.
  • Simple partial seizures with elementary symptomology; consciousness is not impaired.
  • Complex partial seizures involving more than one symptom (complex symptomology) and during which consciousness is impaired.
  • Partial seizures, which may evolve into secondarily generalized seizures.

Individuals with Epilepsy may or may not have concurrent conditions such as intellectual disability or other physical limitations. The primary concern is the social stigma attached to the disorder as it has a sudden onset where the individual is engaging in normal activities one minute and is totally nonfunctional the next. The seizure itself is often alien and frightening to observers, and the person experiencing the convulsion is not in control. Unfortunately, all societies desire and respect predictability and regularity.

Autism Spectrum Disorder/Pervasive Developmental Disorders

Pervasive Developmental Disorders are characterized by severe and pervasive impairment in several areas of development: reciprocal social interaction skills, communication skills, or the presence of stereotyped behavior, interests, and activities. The qualitative impairments that define these conditions are distinctly deviant relative to the individual’s developmental level or mental age. Pervasive Developmental Disorders include Autistic Disorder, Rett’s Disorder, Childhood Disintegrative Disorder, Asperger’s Disorder, and Pervasive Developmental Disorder Not Otherwise Specified.

The Pervasive Developmental Disorders are sometimes observed with a diverse group of other general medical conditions. With most cases of Autistic Disorder, there is an associated diagnosis of Intellectual Disability, which can range from mild to profound.

Each person with an Autism Spectrum Disorder will have her or his own individual pattern of autism which may have an onset at birth or develop later in childhood. Such patterns may include deficits in social or language skills and unusual behaviors. Because the symptoms vary in type and severity among affected individuals and are often a unique combination for each individual, the range can be associated with an unlimited spectrum, thus the term Autism Spectrum Disorder.

Asperger’s Syndrome is the mildest form of Autism and individuals may become obsessively interested in a single object or topic and social skills are markedly impaired. Language is usually not impaired in a diagnosis of Asperger’s Syndrome.

Among the spectrum, a variety of the following symptoms may be present:

  • Qualitative impairment in social interactions
  • Restricted, repetitive, and stereotyped patterns of behavior, interests, and activities
  • Clinically significant impairment in social, occupational, or other important areas of functioning
  • Qualitative impairments in communication such as a delay or lack of spoken language, inadequate speech, stereotyped and repetitive language or idiosyncratic language, and/or lack of varied, spontaneous social imitative play appropriate to developmental level
  • Delays or abnormal functioning in at least one of the following areas, with onset prior to age 3 years: (1) social interaction, (2) language as used in social communication, or (3) symbolic or imaginative play