What is Intellectual Disability | Types of Intellectual Disability


Intellectual disability usually refers to conditions that affect the thinking, learning and neurodevelopmental process of an individual. Intellectual disability could lead to other types of disability and other health conditions which is why it is important to take the first signs or symptoms of intellectual disability seriously.

Signs usually appear in childhood and progress through adulthood with behavioral, learning and thinking problems being the most prevalent signs.

In this article, you will find information on intellectual disability, types of intellectual disability, causes of intellectual disability and possible treatment.

What is Intellectual Disability?

Intellectual disability is a neurodevelopmental disorder which limits the individual’s ability to function normally and perform everyday activities.

 A person is only considered to be intellectual disabled if they have an IQ below 70 in addition to deficits in two or more behaviors that affect the general living.

People with intellectual disability generally have problems with process information, communicating and functioning normally. Symptoms of intellectual disability usually appear in childhood and children with could show signs of slow learning, delays in talking and walking, inability to solve simple problems, and academic problems.

An Intellectual disability could be caused by genetic or environmental factors. It can also be caused by problems during pregnancy and birth, brain injury and illnesses 

Types of Intellectual Disabilities

Fragile X Syndrome

Fragile X Syndrome is a genetic disorder that affects the intellectual capability of the affected person. Although it affects both males and females, the symptoms are usually more severe in males than females which is because they possess only one X chromosome.

Fragile X Syndrome is caused by the mutation of a gene on the X chromosome. The mutation of the fragile X mental retardation 1 (FMR1) gene leads to abnormality and affects the gene’s ability to make the body produce the FMRP protein which is needed for the brain to function properly. Thus, people with this disorder have little or none of this protein in their bodies.

The symptoms of the disorder usually appear early and they are intellectual, physical and mental. Males with this disorder usually have an IQ below 55, however, the physical and mental symptoms are more pronounced.

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  • Mental symptoms include language and speech delay, inability to learn how to walk or crawl, temper tantrums, anxiety, poor impulse control, extreme sensitivity to light or sound, hyperactivity, and aggressive behavior in boys.
  • Physical symptoms include a large head, large ear and forehead, loose joints, flat feet, and large testicles.

The symptoms in girls are quite different from those of boys. Most girls with the syndrome wouldn’t have problems with learning and development but could have trouble getting pregnant.

Treatment for this disorder aims at helping people with development and learning problems and using medication to control behaviors problems.

Down Syndrome

Down syndrome is a genetic disorder that affects the intellect and physical appearance of the affected person. The genetic disorder is caused by an extra chromosome which completely alters the mental, physical and intellectual state of the affected person.

People with this condition generally have a flat head, low muscle tone, flexible ligaments, stunted growth, hearing and vision disorder, and mental impairment,

Doctors believe that Down syndrome is caused by the presence of an extra chromosome 21, however, it remains unclear why someone would get an extra copy. Genetic, biological and environmental factors do pose a risk for the syndrome which means anyone can get it even though if it has never been in the family history.

The chances of someone having Down syndrome may depend on how old the mother was during the time of birth. Doctors believe that women above 35 have a higher chance of giving birth to a child with Down syndrome.

There are 3 types of Down syndrome –  Trisomy 21, Translocation Down Syndrome, and Mosaic Down Syndrome. Although all types have similar symptoms, people with Mosaic down syndrome which is the rarest, tend to have fewer signs and symptoms of the syndrome.

People with this syndrome have an increased risk of other health problems like heart disease, cancer, thyroid diseases, and other disorders.

Congenital Hypothyroidism

Hypothyroidism is when the thyroid gland is underactive and does not produce enough of some important hormones. This affects how fast the body uses energy and slows down the chemical activity in cells. When it happens in a baby, it is called Congenital Hypothyroidism.

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There are several causes of the condition like birth defects and nutrition deficiency. Some cases are due to incomplete formation of the thyroid gland in the baby during pregnancy. Iodine deficiency is also another cause of the condition, however, it is believed that are many other unknown causes and genetics could play a role in the development of the condition.

Symptoms of congenital hypothyroidism include jaundice, constipation, prolonged sleep, large swollen tongue, pale skin, swelling around the eyes, and a weak cry.  

Congenital hypothyroidism can be treated by making up for the absence of hormones that the thyroid gland is supposed to produce. Treatment is often a pill of the thyroid hormone which is inexpensive and effective.

Congenital hypothyroidism is a serious condition that can lead to growth failure and permanent intellectual disability if the baby is not treated a few months after being born.  

Prader-Willi Syndrome

Prader-Willi Syndrome is caused by the loss of function of some specific genes. The genetic disorder is quite complex and rare. People with the syndrome show signs of mental, physical and behavioral problems.

The syndrome can be inherited from the parents of the child, however, the cause of the loss of function in the genes are still unknown. Environmental and biological factors do not increase the risk of having a child with the syndrome. Although Prader-Willi syndrome is a genetic disorder, most people with the disorder did not inherit it from their parents.

Symptoms of the disorder can appear while the baby in the uterus or during childhood and adulthood. Prader-Willi syndrome is the leading cause of genetic obesity in children as children with the syndrome have an uncontrollable need for food and would steal food at any given chance.

They spend more time eating which increases the risk of them having diabetes 2. The disorder also causes intellectual impairment and behavioral problems.

Symptoms of the disorder include intellectual delay, sleep disorders, weight gain, short stature, delay puberty, speech delay, and obesity. Intellectual disability in people with Prader-Willi syndrome is severe, mild or moderate with mild and moderate intellectual disabilities being the most common types.

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Although there is no known cure for the disorder, there is treatment that can improve the quality of life of people with the disorder

Fetal Alcohol Spectrum Disorder (FASD)

FASD refers to several conditions that are as a result of exposure to alcohol while in the womb.
FASDs are one of the few disorders that can easily be prevented. The child can have FASD if alcohol enters the bloodstream and reaches the developing fetus or causes higher blood alcohol concentrations in the developing baby than in the body.

Alcohol interferes with the delivery of oxygen and nutrition to the fetus and also inhibits the development of tissues and organ in the baby. There is no safe amount of alcohol to consume during pregnancy and any amount puts the baby at risk of the disorder.

There are various types of FASDs with the most severe being fetal alcohol syndrome (FAS) that leads to birth defects and neurodevelopment disorders.

Other types of FASDs are alcohol-related neurodevelopment disorder (ARN) which is characterized by intellectual disability and behavior problems and Alcohol-Related Birth Defects (ARBD) which is characterized by problems affecting the kidney, heart, bones or hearing.  

People with FASDs usually have stunted growth, intellectual disability, delayed development, poor memory, poor judgment skills, rapid changing mood, hyperactivity, and vision and hearing problems

The disorders can lead to other disabilities like substance abuse, aggression, attention-deficit/hyperactivity disorder (ADHD), mental health disorder and suicide

There is presently no cure for FASDs but treatment could help improve the quality of life of the affected person, however, prevention is always the best approach to FASDs.

More on Intellectual Disability

Intellectual Disability is usually due to a condition that affects the neurodevelopment of the individual. This condition is usually transferred from parent to child, however, there are cases where infections of the brain and brain trauma (injury) can lead to intellectual disability.

Birth defects like congenital hypothyroidism are other causes of intellectual disability that are not related to genetics.

Intellectual disability doesn’t only affect the learning and thinking ability of the affected person but also their emotional and mental state of mind. Some intellectual disabilities would lead to mental disorders especially for people with intellectual disabilities who do not have access to proper medical care.


Intellectual disabilities can’t be cured by any medical process, however, treatments can help improve the quality of life of the affected individual. For those with mental and emotional problems, antidepressants and other types of medications would help make them feel better and live fairly normal lives.

Some mental disabilities are also referred to as intellectual disabilities as they are both related, however, mental disabilities are broader while intellectual disabilities refer to impairments in the intellectual capacity of an individual.

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