Intellectual and Developmental Disabilities

Intellectual and developmental disabilities are differences usually present at birth that affect a person’s physical, intellectual, and emotional development. They may affect multiple systems in the body, and their symptoms extend throughout life.

Overview

Intellectual and developmental disabilities are differences that are usually present at birth and that uniquely affect how a person develops physically, intellectually, and emotionally. Many of these conditions affect multiple body parts or systems.

Intellectual disability starts any time before a child turns 18 years old. It involves differences in two areas:

  • Intellectual functioning: the ability to learn, reason, problem solve, and other related skills
  • Adaptive behavior: everyday social and life skills

Developmental disabilities are a broader category. They cover often lifelong challenges that can be intellectual, physical, or both. The term “intellectual and developmental disabilities” describes situations in which intellectual disability and other disabilities are both present.

The exact definition of intellectual and developmental disabilities, as well as the different types or categories of intellectual and developmental disabilities, may vary depending on the source of the information.

For example, within the context of education and the Individuals with Disabilities Education Act (IDEA), a law that aims to ensure educational services to children with disabilities throughout the nation, the definition of intellectual and developmental disabilities and the types of conditions that are considered part of this umbrella might be different from the definitions and categories used by the Social Security Administration (SSA) to provide services and support for those with disabilities. These definitions and categories might also be different from those used by healthcare providers and researchers.

Signs and Symptoms

The effects of intellectual and developmental disabilities depend on the body systems they affect.

Nervous system disorders affect how the brain, spinal cord, and nervous system function, which can affect intelligence and learning. These conditions can also cause behavioral disorders, speech or language difficulties, seizures, and trouble with movement. Some examples of IDD conditions that involve the nervous system include cerebral palsy, Down syndrome, Fragile X syndrome, and autism spectrum disorder (ASD).

Sensory system disorders affect the senses (sight, hearing, touch, taste, and smell) or how the brain processes information from the senses.

Metabolic disorders affect how the body uses food and other materials for energy and growth. Problems with these processes can disrupt overall body and brain functions. Phenylketonuria and congenital hypothyroidism are examples of metabolic conditions that can lead to intellectual and developmental disabilities.

Degenerative disorders may not appear at birth. A person with a degenerative disorder may seem typical at birth and meet usual developmental milestones for the first few years of their life, but then experience disruptions in skills, abilities, and functions. In some cases, the disorder may not be detected until the child is an adolescent or adult. Some degenerative disorders result from untreated metabolic problems.

Some signs of intellectual and developmental disabilities include:

  • Sitting up, crawling, or walking later than other children of similar ages
  • Learning to talk later or having difficulty speaking
  • Finding it hard to remember things
  • Having trouble understanding the rules of social behavior
  • Having difficulty understanding the outcomes of actions
  • Having trouble solving problems

Causes and Risk Factors

Intellectual and developmental disabilities have a variety of causes. Some possible causes include:

  • Genetic mutations, additions, or deletions, for example, most cases of Rett syndrome are caused by a change in the MECP2 gene
  • Chromosome abnormalities, such as an extra or missing chromosome: for example, Down syndrome results from having an extra copy or part of a copy of chromosome 21
  • Exposure to certain substances in the womb, for example, exposure to alcohol while in the womb can result in fetal alcohol spectrum disorder (FASD)
  • Infections during pregnancy, for example, infants whose mothers had cytomegalovirus during pregnancy may have hearing, vision, and neurological problems
  • Problems during childbirth, for example, an umbilical cord wrapped around a baby’s neck during delivery could cut off blood and oxygen to the brain
  • Preterm birth: when a baby is born significantly earlier than the typical nine months after conception, there may be associated intellectual and developmental disabilities

Diagnosis

Healthcare providers typically diagnose an intellectual disability through a test of intelligence or cognition. This type of test helps the healthcare provider examine a person’s ability to learn, think, solve problems, and make sense of the world.

Clinicians also observe a child’s behavior for signs of a disability and assess adaptive behavior. Adaptive behaviors include coping skills and other behaviors that show how a child interacts with other people. Healthcare providers use this information to assess whether the person has the skills needed to care for themselves and interact with others.

In addition, developmental milestones can be monitored to identify delays such as delays in walking or talking that could indicate an intellectual and developmental disability.

Some conditions that lead to intellectual and developmental disabilities may be diagnosed with a blood test, ultrasound, or another method, depending on the condition. These tests may be conducted after birth or during pregnancy.

Newborn Screening

Newborn screening tests blood samples taken from newborns while they are still in the hospital to help identify certain serious or life-threatening conditions, including some that lead to intellectual and developmental disabilities. Most tests use a few drops of blood obtained by pricking the infant’s heel. If a screening test suggests a problem, the infant’s doctor will follow up with further testing.

Prenatal Screening

Healthcare providers often recommend that certain pregnant women have their fetuses tested prenatally for conditions that cause intellectual and developmental disabilities.

Maternal blood screening for fetal DNA is often performed to identify whether a fetus has a higher risk of certain chromosomal anomalies (including Down syndrome) or other conditions. If the results of this blood test suggest a possible concern, additional testing may be suggested.

Amniocentesis is a test usually performed to determine whether a fetus has a genetic disorder. A doctor takes a small amount of fluid from the womb using a long needle. Amniotic fluid contains cells with genetic material identical to that of the fetus. A laboratory grows the cells and examines their genetic material. Amniocentesis can detect several conditions that result in intellectual and developmental disabilities, including Down syndrome and certain types of muscular dystrophy.

Chorionic villus sampling extracts cells from inside the womb to determine whether the fetus has a genetic disorder. A doctor takes cells from the chorionic villi, which are tissues in the placenta, the organ that nourishes the fetus. Like amniocentesis, chorionic villus sampling can test for chromosomal disorders such as Down syndrome and some other genetic problems. It can be done earlier in pregnancy than amniocentesis, but it carries a higher risk of miscarriage. Healthcare providers usually only recommend this test for women at high risk of carrying a fetus with a genetic condition.

Treatment and Management

Many intellectual and developmental disabilities have no cure, but there are often ways to treat their symptoms. Treatment options vary by condition.

  • Children with Down syndrome, Fragile X syndrome, Rett syndrome, and other intellectual and developmental disabilities can often benefit from speech therapy, occupational therapy, and exercises to improve gross-motor and fine-motor skills. Special education and the efforts of parents, educators, and healthcare practitioners to encourage social contact and communication can also help. For children with Down syndrome, surgery can help correct heart defects that may be present.
  • A variety of treatment options are available to help with the symptoms of autism spectrum disorders, including behavioral, occupational, physical, and speech-language therapy. Educational specialists can also help guide the child’s school experiences.
  • Treatment for hypothyroidism includes daily oral hormone treatment.
  • Metabolic disorders are often treated with dietary or nutritional interventions. For example, the most effective treatment for phenylketonuria, a metabolic condition that can cause intellectual and developmental disabilities, is a special diet that carefully limits intake of the amino acid phenylalanine. People with this condition who begin this diet at birth or shortly after can develop normally and may have no symptoms if they stay on the special diet for their entire life.

Find Clinical Trials

Clinical trials uncover better ways to prevent, diagnose, treat, and understand diseases and conditions. To ensure results apply to everyone, volunteers of all ages, sexes, and backgrounds, including both healthy individuals and those with specific medical conditions, are needed. Find clinical trials on intellectual developmental disabilities.

Find Treatment

If you suspect your child has an intellectual and developmental disability, start by talking with the child’s healthcare provider. If the healthcare provider notices signs of a problem, ask for a referral to a developmental pediatrician or another specialist.

You can also contact your local early-intervention agency for children under 3 years of age, or your public school for children aged 3 years or older.

Your local school system can help you get a diagnosis for your child’s condition and evaluate the child’s educational needs as part of the Individuals with Disabilities Education Act (IDEA), which aims to ensure educational services for children with disabilities throughout the nation.

Community Support

The following organizations provide information, services, and support for people with intellectual and developmental disabilities and their families:

General Information

Information About Developmental Milestones

Services, Resources, and Support

Note: This resource list is for informational purposes only. It is not comprehensive, and an organization’s inclusion does not constitute an endorsement by NIH.  

Research Information

The National Institutes of Health (NIH) is the largest public funder of biomedical research in the world. NIH invests most of its budget in medical research seeking to enhance life and to reduce illness and disability. NIH-funded research has led to breakthroughs and new treatments helping people live longer, healthier lives, and building the research foundation that drives discovery.

NIH supports and conducts research to understand the causes and effects of intellectual and developmental disabilities and to identify effective therapies.

NIH research on intellectual and developmental disabilities focuses on several areas, including:

  • Genetic and developmental causes
  • Ways that these conditions affect learning, communication, cognition, and memory
  • How the family and community interact with people who have intellectual and developmental disabilities
  • The effect of individual factors on social interactions, behavior, and emotions

NIH supports several research programs related to intellectual and developmental disabilities, including:

  • Autism Centers of Excellence (ACE) Program
  • Eunice Kennedy Shriver Intellectual and Developmental Disabilities Research Centers (EKS-IDDRCs)
  • Centers for Collaborative Research in Fragile X Syndrome and FMR1-related Conditions
  • Paul D. Wellstone Muscular Dystrophy Specialized Research Centers (MDSRCs)

Find NIH-funded research projects using NIH RePORTER, a searchable database of current and past research projects supported by NIH and other federal agencies.