What Are the Symptoms of Intellectual Disability?

ID, also called intellectual development disorder, is lower than average intelligence that causes challenges with daily tasks and overall functioning.

Intellectual disability has replaced the term “mental retardation,” a term that has become offensive to many people and has resulted in misunderstandings about the disorder and people who have it.

Healthcare professionals use the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) to diagnose ID.

A diagnosis is based on three sets of criteria:

1. Intellectual challenges in areas such as:

• learning, both academic and experiential, such as talking
• reasoning
• planning
• problem-solving
• judgment
• abstract thinking

2. Adaptive functioning difficulties caused by intellectual challenges for skills like:

• communication
• socializing
• independent living

3. Early onset of the above intellectual and adaptive symptoms:

• presence of symptoms during childhood or adolescence

The DSM-5 updated criteria to put less emphasis on diagnosing ID based on a threshold of symptoms in each category. Now, healthcare professionals are urged to look holistically at the person’soverall functioning.

ID can be diagnosed in children over 5 years old when IQ testing is more reliable. Children under 5 with symptoms are considered to have a global developmental delay (GDD). A diagnosis of GDD may predict a future diagnosis of ID.

Sometimes children over 5 years old have ID symptoms but have factors that interfere with testing, such as visual or hearing impairment. In cases like this, doctors may give them the diagnosis of unspecified intellectual disability and reassess them later.

ID symptoms become clearer as children age since they miss typical developmental milestones. For that reason, ID is almost always diagnosed by the time a child reaches 18 years old.

Some children with mild ID fit in well socially. They can acquire practical skills such as self-care and academics up to the intermediate elementary school level. They’re slower than average children their age in most areas but can integrate with their peers in many settings.

Others with ID are more noticeably different in how they interact with others. Some people with ID can communicate and learn self-care, whereas others are dependent and need 24-hour care.

Symptoms may not look the same in every person with ID. IQ test results and the amount that ID impacts their ability to function determine the ID severity diagnosed.

Here are symptoms for the three categories of diagnosis:

Intellectual deficit

• late learning letters, numbers, or other intellectual milestones
• speech delay or trouble communicating clearly
• inability to connect actions with consequences
• trouble with memory
• difficulty following instructions
• may be able to master basic academics but unable to progress beyond elementary level

Adaptive functioning deficit

• late to potty train, dress, and feed self
• sitting, crawling, or walking later than other children
• doesn’t know how to follow social rules
• poor social judgment
• struggles with emotional regulation
• requires repeated social interventions on the school playground

Developmental period onset

The developmental period refers to childhood and adolescence. This is when differences from peers become noticeable.

Even though ID is often present before birth, parents may not see signs of mild ID in their child until they enter school. At this point, school staff, who have extensive experience with many young children, notice differences from age peers that parents may have missed.

Sometimes ID symptoms show up in younger children as delays in motor skills or language use.

ID severity levels

Intellectual disability has four severity levels.

Mild:

• IQ range of 50 to 69
• 85% of ID cases
• able to live independently with minimal support
• can integrate with peers and conform socially
• achieve academics up to intermediate elementary school level
• typically are in specialized education classes
• learn how to talk later but can communicate well once they learn

Moderate:

• IQ 36 to 49
• 10% of ID cases
• able to live independently with moderate support such as in a group home
• noticeable delays in talking and understanding language
• altered speech or some difficulty communicating
• can participate in some social activities
• able to learn basic reading, writing, and counting

Severe:

• IQ 20 to 35
• 3.5% of ID cases
• requires regular supervision for safety and daily self-care assistance
• needs direction and social supervision
• may learn basic self-care
• significant motor impairment

Profound:

• IQ less than 20
• 1.5% of ID cases
• incapable of self-care
• requires care 24-hours a day
• inability to understand communication from others
• non-verbal communication
• may experience immobility

Individuals with ID often live with co-occurring conditions, including autism spectrum disorder, cerebral palsy, epilepsy, attention deficit hyperactivity disorder (ADHD), and depression.

While ID is an intellectual deficit that interferes with multiple areas, a learning disorder (LD) is specific to a specific group of academic skills, such as language or math. Dyslexia is one example.

An LD is related to how someone learns, not their intelligence. Unlike children with ID, those with learning disabilities typically have average to above-average intelligence. With support for their LD, they can graduate from high school and move on to post-secondary education.

There are several ways a child can end up with ID. Sometimes the cause of individual cases remains unknown.

Causes of ID include:

• trauma before birth, such as an infection in the mother or exposure to drugs or alcohol
• trauma during birth, such as lack of oxygen
• chromosomal abnormalities, like Down syndrome and fragile X syndrome (FXS)
• head injury
• severe childhood infections, such as meningitis or measles
• severe malnutrition, lead exposure, or mercury poisoning as a young child

Healthcare professionals use standardized intelligence testing to identify the severity level of ID and clinic assessments to observe adaptive deficit.

The DSM-5 no longer uses IQ as the only criteria for diagnosis because it may not accurately reflect how well a person can function overall. Not everyone with a below-average IQ needs support.

Along with IQ, doctors assess three areas of functioning:

• Conceptual: practical academic skills such as simple math, reading, reasoning, memory, acquired knowledge
• Social: friendships, communication, empathy, social judgment, the ability to follow social rules
• Practical: personal care, responsibilities, organization, ability to stay on task

Healthcare professionals interview the person they’re assessing and gather information from family members, caregivers, and teachers.

A careful screening and complete medical history are important to identify or rule out other conditions that might cause the same symptoms. For example, both ID and autism can cause communication difficulties and atypical behaviors.

Your family doctor can begin the diagnostic process. If the person being assessed is a child, a developmental pediatrician can take on the responsibility.

An ID is a low IQ that results in impaired intellectual and adaptive functioning.

There are various ID symptoms, depending on the individual’s severity level. Sometimes the only sign you see is an inability to keep up at school. Other times it’s very clear that the person has profound differences.

Most people with ID have a mild form. With early intervention and support, people with mild ID can live full lives. They’re able to live independently, hold down jobs, and have a social life when they get older.