Intellectual Disability: Definition, Characteristics, Classification, Causes, etc

Intellectual Disability: Definition, Characteristics, Classification, Causes, etc


mentally disabled

Definition of Mental Disabilities

Mental retardation is a condition in which a child or individual with below average intellectual disabilities experiences various obstacles from various aspects as a result of a disturbance in the development of the central nervous system (brain). As revealed by Marlina (2015, p. 16) that mental retardation is a condition characterized by mental abilities that are far below average, have obstacles in social adjustment, are related to organic damage to the central nervous system and cannot be cured and requires systematic educational services, multidisciplinary services and individually designed (Marlina, 2015, p. 16).



Meanwhile, according to Somantri (in Asrori, 2020, p. 91) revealed that mentally retarded or also known as mentally retarded are individuals who have limited intelligence so that it is difficult for them to take part in educational programs in ordinary schools classically so that they require special education services that are adapted to the child’s abilities.


Meanwhile, the American Association of Mental Deficiencies (AAMD in Marlina, 2015, p. 16) defines mental retardation as a complex condition that shows low intellectual abilities and experiences obstacles in adaptive behavior. That is, a person cannot be categorized as mentally retarded if he does not experience low intellectual impairment without being accompanied by behavioral barriers that are unable to adapt.


In detail, the adaptive behavior or self-adjustment in question can be seen from seven aspects which include:



retarded in the development of sensory motor skills,

hampered in communication skills,

handicapped in self-help skills,

obstacles in socialization

hampered in applying academic skills in everyday life,

hampered in assessing the environmental situation appropriately, and

hampered in assessing social skills (Rochyadi in Marlina, 2015, p. 16).

More specifically, AAMD (in Asrori, 2020, p. 91) states mental retardation as a disorder that includes below-average general intellectual functioning, namely an IQ of 84 and below based on tests and appears before the age of 16 years.


Meanwhile, according to Pujiastuti (2021, p. 57) mentally retarded is another name for mental retardation which consists of the word “tuna” which means “loss”, and “grahita” which means “mind”, thus mentally retarded, mentally retarded or mentally defective) or mentally retarded is a term used to name a child or someone who has an intelligence capacity at the basic level, specifically having an IQ score below 70 based on the standard intelligence test.



It can be concluded that mental retardation is a condition of individuals who have low intellectual capacity based on IQ scores below average so that they experience various adaptive or self-adjustment barriers such as communication to self-help skills as a result of obstacles or organic disturbances in the nerve center (brain).



Traits of Mental Disability

According to Marlina (2015, p. 17) mentally retarded children can be identified by the following characteristics.


Unbalanced physical appearance, for example the head is too small or large.

Unable to take care of self for age

Delayed speech/language development.

There is no or very little attention to the environment (blank gaze).

Poor coordination of movements (movements are often uncontrollable).

Frequent saliva (liquid) from the mouth (drooling).

Characteristics of Mental Disability

According to Gunadi (2011, p. 139) mentally retarded children have the following characteristics.


Having difficulty learning new things and abstract knowledge, mentally retarded people also quickly forget what they are learning if they are not trained continuously.

Have physical disabilities and lack in the development of their movements. The majority of people with mental retardation in the severe category have limitations in physical movement, such as being unable or unable to walk smoothly.

Have difficulty taking care of yourself. The average mentally retarded person from the brand cannot take care of their own needs, such as dressing, eating, and taking care of their own hygiene.

Their lack of ability to interact with the surrounding environment. People with mild mental retardation can still play with their friends, but those with severe mental retardation cannot do these things.

People with mental retardation sometimes behave unnaturally continuously, like to twirl their fingers in front of their faces by banging their heads or biting themselves.

Classification of mentally retarded

According to AAMD (in Lisinus & Sembiring, 2020, p. 90) the classification of mental retardation is divided into three groups, some of which are as follows.


Mild mental retardation (able to educate)

With mild mental retardation, they have intelligence with an IQ ranging from 50-70, mild mental retardation has the ability to be able to develop in the areas of academic studies, social adjustment, and work ability, able to adapt to the environment, able to do semi-skilled work, and simple work.

Moderate mental retardation (able to train)

The IQ level of intelligence possessed by mentally retarded people is in the range of 30-50, they are learning school skills for functional purposes, able to perform self-care skills, able to adapt to the environment, able to do routine work carried out under the supervision of the closest person.

Severe and Very Severe Mental Disability (Capable of Treating)

Severe mental retardation is a mental retardation that has almost no ability to be trained in taking care of itself, and the level of intelligence IQ possessed by severe mental retardation is less than 30. With severe mental retardation they are still able to be trained in taking care of themselves, communicate simply, and can adapt to the environment but very limited.

Classification of mental retardation based on clinical type

According to Asori (2020, p. 91) based on the causes of intelligence disorders in terms of organic abnormalities or clinical types, mentally retarded can be classified into three types, which include the following.


Down Syndrome

Down syndrome can be recognized based on certain physical characteristics, such as a small round head (brachicephaly) and flat, imperfect. The fontanel does not close quickly, becomes hard and often never closes at all. The shape of the teeth is abnormal, the ribs and spine are often deformed. Thick or cleft lip, very large or very small ears. The skin is dry and rough, but often soft and tender like a baby’s skin. Her cheeks are rosy. His hands were soft, big and wide as if they contained water. The soles of the feet are flat, the belly is distended and the navel is protruding. The joints and muscles are stiff (Semiun in Asrori, 2020, p. 92).


Causes of Down’s Syndrome

Down syndrome is characterized by an extra chromosome or third chromosome on the 21st chromosome, causing the number of chromosomes to be forty-seven instead of forty-six as in normal individuals. Down syndrome occurs in about one in eight hundred births. This condition usually occurs in the 21st chromosome pair in the egg or sperm fails to divide normally so that it can result in extra chromosomes.


Certain chromosomal abnormalities can result in metabolic abnormalities which further negatively affect brain development and lead to mental retardation. An example is down syndrome or mongolism. Called mongolism because sufferers often have slanted eyes, like Mongolians. The cause is an abnormality in the chromosomes (the presence of trisomy on chromosome 21). The advanced age of the father and mother, namely over 40 or even 50 years when the baby is conceived or born, has an effect on the occurrence of these chromosomal abnormalities.



Therefore, couples who are in their mid-30s or older, who are expecting a baby, often undergo prenatal genetic testing to detect Down syndrome and genetic abnormalities. Down syndrome can be traced through damage to the mother’s chromosomes in about 95% of cases, while the rest is damage to the father’s sperm (Zenal et al in Asrori, 2020, p. 91).


Congenital hypothyroidism

Congenital hypothyroidism is a condition of decreased or non-functioning thyroid gland that is acquired from birth (Asrori, 2020, p. 92). Symptoms and signs that may appear: lethargy (decreased activity), jaundice (yellow), macroglossy (big tongue), umbilical hernia (bulging), flat nose, constipation, dry skin, skin mottling (mottling), easy choking, hoarseness, hypotonia (decreased muscle tone), enlarged fontanel, distended stomach, cold easily (cold intolerance), myxedema (swollen face) (Mranani in ASrori, 2020, p. 92).


Causes of Congenital Hypothyroidism

Hypothyroidism occurs due to anatomic abnormalities or metabolic disorders in the formation of thyroid hormone or iodine deficiency. Thyroid hormone, namely thyroxine which consists of Triiodotironine (T3) and Tetra-iodotironine (T4), is a hormone produced by the thyroid gland (thyroid glands). Its formation requires the micronutrient iodine. This hormone functions to regulate body heat production, metabolism, bone growth, heart, nerves, and brain growth and development. This hormone is very important role in infants and children who are growing. Deficiency of thyroid hormone in infancy and early life, can inhibit growth (dwarf / stunted), and mental retardation mental retardation.


Hydrocephalus is an increase in the volume of cerebrospinal fluid in the ventricular and subarachnoid spaces (Asrori, 2020, p. 93). In children under six years, including neonates, an enlarged head (macrocephaly) will be seen. Percussion of the child’s head gives a distinctive sensation. This illustrates the widening of the sutures. The veins on the scalp are very prominent, especially when the baby cries. The eyes of people with hydrocephalus show a distinctive picture, namely the setting-sun sign (the sclera that appears above the iris) (Afdhalurrahman in Asrori, 2020, p. 93).


Causes of Hydrocephalus

The condition of hydrocephalus can be caused by an imbalance in the production and absorption of cerebrospinal fluid (Asrori, 2020, p. 93). Hydrocephalus is congenital, usually appearing in infancy. Hydrocephalus that appears after 6 months of age is usually not congenital. Cases of hydrocephalus were described by Hippocrates, Galen, and Muslim doctors in the early Middle Ages, they believed that this disease was caused by accumulation of extracerebral fluid. Approximately 40-50% of infants with grades 3 and 4 intraventricular hemorrhage will develop hydrocephalus. Hydrocephalus that arises from complications of bacterial meningitis often occurs in infants, usually the bacteria that cause it are still difficult to identify because patients often come after their sepsis has been treated.


Causes of Mental Disability

There are various things that can cause a child to become mentally retarded, starting from infection, physical trauma, genetic disorders, premature birth, and so on. However, broadly speaking, the main causes of mental retardation come from outside, such as exposure to X-Rays, the influence of toxic substances, brain damage at birth, or infection with a disease virus and originates from within, such as abnormalities in the formation of chromosomes. As stated by Lisinus & Sembiring (2020, pp. 96-98) that the factors that cause mental retardation are as follows.


Heredity Factor

Based on research conducted on mentally retarded children, it was explained that around 5% of mentally retarded children are caused by hereditary factors, this is caused by inherited abnormalities in genes, such as fragile X syndrome, damage to one of the genes such as phenylketonuria.

Before Birth

Some mentally retarded children are caused by their parents when they were pregnant at 12 weeks of gestation, their mothers drank alcohol, besides that the rubella virus is also the cause of mental retardation in children.

Damage At Birth

This damage can be caused by a difficult birth process, so in this case equipment is needed to help the child be born.

Metabolism and Nutrition Disorders

Failure in metabolism and failure to meet nutritional needs can result in physical and mental disorders in individuals. Symptoms that can be seen from the presence of metabolic and nutritional disorders are nerve spasms, as well as behavioral abnormalities, large skull, wide and short palms, short neck, large and protruding tongue, stiff joints, abnormal height , disproportionate body frame, etc.

Trauma and Radioactive Substances

Brain trauma that occurs in the head can cause intracranial bleeding resulting in defects in the brain, usually caused by difficult births that require assistive devices. X-ray radiation or radiation while the baby is in the womb causes microcephaly mental retardation. Fetuses that are exposed to radioactive substances in the first three to six weeks of pregnancy often cause abnormalities in various organs, because at this time the embryo is easily affected.

Problems at Birth

Birth accompanied by hypoxia (seizures and shortness of breath) ensures that the baby to be born suffers from brain damage.

Environmental factor

Lack of personal contact with children, for example by not talking to them, smiling, playing which results in tense, cold and self-closing attitudes. This condition will have a bad influence on the development of children both physically and mentally intellectually.

Biochemical Damage

According to Waiman and Gerritsen (in Lisinus & Sembiring, 2020, pp. 96-98), currently there are more than 90 diseases that can cause metabolic abnormalities since birth, these can be inherited genetically in the sense that they are inherited in nature.

Impact and Problems of Mental Disability

According to Amin (in Muhtar & Lengkana, 2019, pp. 43-44) there are several impacts of problems experienced by mentally retarded persons, which include the following.


Problems in everyday life

This problem is related to health and self-maintenance in everyday life. Problems that are often encountered in the way they eat, brush their teeth, wear shoes, worship, and so on.

The problem of learning difficulties

The intellectual limitations of mentally retarded students cause them difficulty in thinking, so it is possible that they always experience difficulties in learning.

Adjustment Problems

Adaptation to the environment is strongly influenced by one’s intelligence, mentally retarded students themselves have intelligence that is below average so that in terms of adaptation to the environment mentally retarded students have difficulty adapting.

Disorders and personality problems

In this condition it can be seen from their behavior, such as they will be silent for quite a long time, the movements they make tend to be hyperactive, irritable, and also easily offended.

Problems with channeling to the workplace

The lives of children with special needs for mental retardation tend to still depend on other people, especially on their families and there are still very few people with mental retardation who are able to live independently. Although it is possible that there are some who are already living independently, this is not proportional to the number of mentally retarded people who are still dependent. The lack of provisions that they get makes it difficult for them to get the job they want.

The problem of using free time

It is normal for mentally retarded students in their behavior to often display bad behavior. Actually, some of them tend to like to stay silent and distance themselves from the crowds of society, but this can be fatal for mentally retarded people because this can foster their desire to commit suicide. Thus, it is necessary to have activities for mentally retarded people in their free time, so that they can distance themselves from dangerous conditions, and not disturb peace in society and in the family.

Problems in language development

Mentally retarded students have difficulty being able to express their thoughts and feelings in words, so they cannot express their situation through words. Mentally retarded students who do not understand what other people express to them, will cause them to experience frustration and feel lonely.

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