ID can be caused by any condition that impairs development of the brain before birth, during birth, or in the childhood years. Hundreds of causes of ID have been identified. However, for approximately one-third of those affected, the cause of their disability remains unknown.

Causes of ID include:

• Pregnancy/delivery problems  (drugs, malnutrition, illness, prematurity)
• Early childhood diseases and accidents
• Fetal Alcohol Syndrome (FAS)
• Exposure to toxins and other environmental health hazards
• Genetic anomalies and disorders

Although developmental disabilities can cause difficulties with major life activities such as language, mobility, learning, self-help, and independent living, many people with ID grow up to lead independent lives. The remaining minority with ID, those with IQs under 50, have significant limitations in functioning. With early intervention, a functional education, and appropriate support as an adult, however, individuals with ID can lead full and satisfying lives.

Intellectual disability occurs when a person has difficulty with general mental abilities. This may impact their:

• Intellectual functioning, such as their learning, judgment, problem solving, abstract thinking, memory, reasoning, and academic skills
• practical functioning, which refers to the ability to function and take care of oneself independently, such as performing personal care tasks, managing money, and performing work, school, or home tasks
• social functioning, which refers to the ability to function normally in society by using skills such as social judgment, communication, understanding and following social rules and cues, understanding the consequences of one’s actions, and making friends.

Three areas of practical/adaptive functioning are considered:

1. Conceptual – language, reading, writing, math, reasoning, knowledge, memory
2. Social – empathy, social judgment, communication skills, the ability follow rules and the ability to make and keep friendships
3. Practical – independence in areas such as personal care, job responsibilities, managing money, recreation and organizing school and work tasks

Some common symptoms of intellectual disability include:

• reaching developmental milestones — such as sitting up, crawling, walking, or talking — later than other children
• difficulty speaking or reading
• difficulty understanding or following social rules or cues
• difficulty understanding the results or consequences of their actions
• difficulty solving problems, thinking logically, or thinking abstractly
• difficulty planning or following schedules or routines
• difficulty remembering things
• difficulty letting others know their needs
• difficulty understanding systems such as the need to pay for things, time, or how to use a phone
• difficulty with social skills
• a reduced ability to perform regular personal care, such as eating, getting dressed, or completing household tasks
• limited functioning in one or more daily activities
• reduced judgment and decision making skills
• difficulty learning from experience
• communicating using nonverbal means, such as expressions and gestures
• difficulty regulating emotions and behaviors

Related and co-occurring conditions

Some mental health, neurodevelopmental, medical and physical conditions frequently co-occur in individuals with intellectual disability, including cerebral palsy, epilepsy, ADHD, autism spectrum disorder and depression and anxiety disorders. Identifying and diagnosing co-occurring conditions can be challenging, for example recognizing depression in an individual with limited verbal ability. However, accurate diagnosis and treatment are important for a healthy and fulfilling life for any individual.

• Attention-deficit/hyperactivity disorder
• Autism spectrum disorder
• Social communication disorder
• Specific learning disorder

Autism spectrum disorder (ASD) is a complex developmental condition that involves persistent challenges in social interaction, speech and nonverbal communication, and restricted/repetitive behaviors. The effects of ASD and the severity of symptoms are different in each person.

ASD is usually first diagnosed in childhood with many of the most-obvious signs presenting around 2-3 years old, but some children with autism develop normally until toddlerhood when they stop acquiring or lose previously gained skills. Autism is a lifelong condition. However, many children diagnosed with ASD go on to live independent, productive, and fulfilling lives. The information here focuses primarily on children and adolescents.

Characteristics of Autism Spectrum Disorders

Autism differs from person to person in severity and combinations of symptoms. There is a great range of abilities and characteristics of children with autism spectrum disorder — no two children appear or behave the same way. Symptoms can range from mild to severe and often change over time.

Characteristics of autism spectrum disorder fall into two categories.

• Social interaction and communication problems: including difficulties in normal back-and-forth conversation, reduced sharing of interests or emotions, challenges in understanding or responding to social cues such as eye contact and facial expressions, deficits in developing/maintaining/understanding relationships (trouble making friends), and others.
• Restricted and repetitive patterns of behaviors, interests or activities:
  hand-flapping and toe-walking, playing with toys in an uncommon way (such as lining up cars or flipping objects), speaking in a unique way (such as using odd patterns or pitches in speaking or “scripting” from favorite shows), having significant need for a predictable routine or structure, exhibiting intense interests in activities that are uncommon for a similarly aged child, experiencing the sensory aspects of the world in an unusual or extreme way (such as indifference to pain/temperature, excessive smelling/touching of objects, fascination with lights and movement, being overwhelmed with loud noises, etc), and others.

Also, while many people with autism have normal intelligence, many others have mild or significant intellectual delays. Additionally, people with ASD are at greater risk for some medical conditions such as sleep problems, seizures and mental illnesses.

Diagnosis and Risk Factors

Early diagnosis and treatment are important to reducing the symptoms of autism and improving the quality of life for people with autism and their families. There is no medical test for autism. It is diagnosed based on observing how the child talks and acts in comparison to other children of the same age. Trained professionals typically diagnose autism by talking with the child and asking questions of parents and other caregivers.

The identified possible red flags for autism spectrum disorder in young children, including:

• Not responding to his/her name by 12 months of age
• Not pointing at objects to show interest by 14 months
• Not playing “pretend” games by 18 months
• Avoiding eye contact or preferring to be alone
• Getting upset by minor changes
• Flapping their hands, rocking their body or spinning in circles
• Having unusual and sometimes intense reactions to the way things smell, taste, feel and/or look.

If there is a strong concern that your child is showing possible signs of autism, then a diagnostic evaluation should be performed. This typically involves an interview and play-based testing with your child done by a psychologist, developmental-behavioral pediatrician, child psychiatrist or other providers.