Types of Intellectual Disabilities | Five Common Types to Know

There are five types of intellectual disabilities that are commonly diagnosed among children today.

We will explore these five common types along with …

• Defining intellectual disabilities (ID)
• Causes
• Helpful resources to reference (found at the end of this post)

Let’s dive in.

What is Intellectual Disability?

Intellectual Disability (ID) is the term used when a child has certain limitations with their cognitive thinking skills.

For instance, they have difficulty processing their thoughts or performing various mental activities associated with learning and problem solving.

With these types of limitations, a child will learn and develop at a slower pace.

Five Most Common Types of Intellectual Disabilities

Here’s a list of the five most common types of intellectual disabilities present today in children and what you need to know.

Fragile X Syndrome (FXS)

FXS is a genetic disorder which is caused by changes in the gene called the fragile X mental retardation 1 (FMR1).

The FMR1 usually makes a protein referred to ‘fragile X mental retardation protein (FMRP)’.

The FMRP is the protein that helps develop normal brain activity.  Children who have FXS do not make this protein.

FXS can impact both boys and girls.

Research shows, ‘about 1 in 7,000 males about 1 in 11,000 females have been diagnosed with FXS.’

Down Syndrome

Down Syndrome is a genetic disorder where the child has an extra chromosome in their body.

Specifically, it is a common birth defect that is caused by having extra gene material, specifically chromosome 21.

To break down the definition of both, chromosomes are groups of genes in the body and chromosome 21 is the tiniest gene, spanning about 48 million base pairs (the building blocks of DNA) and representing 1.5 to 2 percent of the total DNA in cells.

In a nutshell, this type of genetic disorder is when there is an extra copy of chromosome 21 (also referred to as trisomy-21).

Cerebral Palsy (CP)

Cerebral Palsy (CP) is the most common neurological childhood disorder and can be defined as brain damage that happens before or shortly after birth which affects movement and muscle tone.

When diagnosed, a doctor will categorize cerebral palsy into four types (spastic, ataxic, athetoid, and mixed) based upon the child’s mobility that has been impacted as well as the number of limbs or body parts that have been affected.

Depending on where the brain damage occurs, mobility can be impacted in the arms, legs, hands, face, and tongue.

Even though CP is permanent damage, the condition will not worsen overtime but can be improved with different treatments such as therapy, medications, surgery, and assistive technology.

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Prader-Willi Syndrome (PWS)

Prader-Willi Syndrome (PWS) is a genetic disorder that occurs in approximately one out of every 15,000 births.

PWS affects both boys and girls with equal frequency and impacts all races and ethnicities.

PWS is recognized as the most common genetic cause of life-threatening childhood obesity.

Prader-Willi Syndrome Association shares PWS was first described by Swiss doctors Andrea Prader, Alexis Labhart, and Heinrich Willi in 1956 based on the clinical characteristics of nine children they examined.

The common characteristics defined in the initial report included small hands and feet, abnormal growth and body composition (small stature, very low lean body mass, and early-onset childhood obesity), hypotonia (weak muscles) at birth, insatiable hunger, extreme obesity, and intellectual disability.

PWS results from an abnormality of chromosome 15, and diagnosis is based on genetic testing.

Fetal Alcohol Spectrum Disorder (FASD)

Fetal Alcohol Spectrum Disorder (FASD) is a condition that can occur when the infant’s mother drank alcohol during pregnancy.

FASD causes brain damage and problems in a child’s growth and development.

Problems can vary from child to child but the defects are permanent and not reversible.

Causes of Intellectual Disability

The cause of ID is based upon different risk factors (such as social, behavioral, educational) and the timing of when the exposure happens to the child either before birth or after birth.

The American Language Speech Hearing Association describes the causes of Intellectual Disability are prenatal, perinatal, and postnatal and “some prenatal causes (e.g., environmental influences) are preventable. Genetic causes account for 45% of ID (Batshaw, Roizen, & Lotrecchiano, 2013).  Down syndrome is the largest genetic cause of ID, and Fragile X syndrome is the largest inherited cause of ID. Fetal alcohol syndrome is the largest environmental cause of ID.”

Is Intellectual Disability Determined by an IQ Test?

The American Association of Intellectual and Developmental Disabilities informs us that the evaluation and classification of intellectual disability is a complex issue.

There are three major criteria for intellectual disability:

1. Significant limitations in intellectual functioning
2. Significant limitations in  adaptive behavior
3. Onset before the age of 18

The IQ test is a major tool in measuring intellectual functioning, which is the mental capacity for learning, reasoning, problem solving, and so on.

A test score below or around 70—or as high as 75—indicates a limitation in intellectual functioning.

Other tests determine limitations in adaptive behavior, which covers three types of skills:

• Conceptual skills—language and literacy; money, time, and number concepts; and self-direction.
• Social skills—interpersonal skills, social responsibility, self-esteem, gullibility, naïveté (i.e., wariness), social problem solving, and the ability to follow rules, obey laws, and avoid being victimized.
• Practical skills—activities of daily living (personal care), occupational skills, healthcare, travel, schedules and routines, safety, use of money, use of the telephone.”

Final Thoughts

Children and adults with intellectual disabilities are truly an inspiration.

I believe ‘Disability’ means ‘Ability’ because our human spirit encompasses many capabilities such as courage and perseverance that no disability can take away.

An incredibly inspiring quote I’m going to share with you by Hellen Keller says, “Your success and happiness lies in you. Resolve to keep happy, and your joy and you shall form an invincible host against difficulties.” 

Wow, isn’t that the truth.  My heart dropped when I read this quote because it is so powerful.

The warriors I have had the pleasure of meeting who have been diagnosed with an intellectual disability, were such a light and joy to be around.

Nothing seems to get them down.  In fact, they seem to bring others UP who are in the presence of their energy!

I hope this information added value to your research efforts in learning more about the types of intellectual disabilities.

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I really do strive to make the content I create as helpful as possible for you…as a fellow parent looking out for their most precious gift.

Thank you for stopping by today!

Helpful Resources

#1.  Frequently Asked Questions (FAQ) you may have about Intellectual Disabilities you can learn about by clicking here.

#2. Checkout the 2nd Edition of A Comprehensive Guide to Intellectual and Developmental Disabilities.

It includes all the critical topics surrounding an individual who has these types of disabilities and is a great guide to reference.

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