Intellectual and Developmental Disability: What Is an IDD?

disabled girl

Intellectual or developmental disability, known as IDD, affects approximately 7.39 million people in the United States, according to a 2019 estimate by the University of Minnesota. Typically present at birth or onsetting in childhood, IDDs adversely impact a person’s physical, neurological, or emotional development.

Two categories of disabilities comprise IDDs: intellectual disabilities and developmental disabilities.

  • Intellectual disabilities involve problems with cognitive functioning or intelligence. These disabilities affect learning, reasoning, and problem-solving, causing deficits in social and life skills.
  • Developmental disabilities are a broader category encompassing intellectual as well as physical disabilities. The Centers for Disease Control and Prevention (CDC) defines developmental disabilities as impairments that affect mobility, learning, language, or behavior.

According to the Eunice Kennedy Shriver National Institute of Child Health and Human Development, IDDs can relate to several systems in the human body.

  • Involving the brain and spinal cord, impairments in the nervous system can adversely affect cognitive functioning, behavior, speech, and language, and may cause seizures and movement difficulties. IDDs that involve the nervous system include autism spectrum disorder (ASD), cerebral palsy, Down syndrome, and Fragile X syndrome.
  • Sensory system issues can cause difficulties with sight, hearing, touch, taste, or smell. The brain may have trouble processing sensory information. Children born prematurely may experience low vision or hearing.
  • Problems in how the body processes food and uses energy for growth implicate the metabolic system, causing IDDs. Metabolic conditions that can lead to IDDs include phenylketonuria and congenital hypothyroidism.

Examples of IDDs

Beginning in childhood, IDDs comprise many impairments that may affect one’s skills and abilities as they navigate school, friendships, and extracurricular activities.

  • Autism Spectrum Disorders (ASD) – Those with ASD experience problems with social interaction and restricted or repetitive behaviors. According to the CDC, ASD typically onsets before age 3 and can be diagnosed as early as 18 months.
  • Cerebral Palsy (CP) – Affecting one in 345 children in the United States, cerebral palsy refers to disorders impacting movement, balance, and posture. Abnormal brain development or injury impairs the ability of a person with CP to control their muscles.
  • Down Syndrome – When a baby is born with an additional copy of chromosome 21, it affects the development of their body and brain, causing mental and physical challenges. One in 700 babies are born with Down syndrome each year.
  • Fetal Alcohol Spectrum Disorders (FASDs) – Alcohol exposure before birth can cause physical problems and difficulties with behavior and learning. FASDs include several disorders that vary in severity.
  • Fetal alcohol syndrome (FAS) sits at the most severe end of the spectrum. Those with FAS have problems with the nervous system and growth, as well as facial differences.
  • Alcohol-Related Neurodevelopmental Disorder (ARND) involves intellectual disability and learning problems.
  • Alcohol-Related Birth Defects (ARBD) involve issues with the heart, kidneys, bones, or hearing.
  • Individuals with neurobehavioral disorder associated with prenatal alcohol exposure have deficits in three areas: thinking and memory, behavior, and daily living.
  • Fragile X Syndrome – A genetic condition, Fragile X syndrome causes changes in a protein essential to brain development, resulting in intellectual disability. The CDC reports that one in 7,000 boys and one in 11,000 girls are born with the condition. Symptoms tend to be more severe in boys than in girls.

Types of Support Available

Several services are available to support those with IDDs and their families.

  • States have IDD agencies offering publicly funded services and resources. Yet the University of Minnesota reports that state IDD agencies serve only 22 percent of individuals with IDDs. Nineteen percent obtained one or more long-term support or services from their state.

    Find an IDD agency near you to begin accessing support.
  • Children with IDDs with limited income and resources can apply for Supplemental Security Income (SSI). SSI benefits are available for children with IDDs that are seriously limiting and that last or are expected to last for at least a year.
  • The Individuals with Disabilities Education Act (IDEA) makes appropriate public education available to children with disabilities. Under the law, children are entitled to an individualized education plan (IEP). Parents can work with teachers, administrators, and their children to create an IEP that addresses classroom needs.
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