Intellectual disability is categorized based on the severity—mild, moderate, severe, and profound.
- Although individuals with moderate intellectual disability (IQ: 36 to 49) have delays in their developmental milestones (a set of skills that a child is expected to attain at a particular age), they attain certain basic adaptive skills including communication and self-care abilities. They may even travel to familiar places within their community. They typically perform poorly at school and have difficulty concentrating.
- A person with severe intellectual disability (IQ: 24 to 36), however, requires supervision or support in social situations. They may be able to understand what others wish to communicate but have a hard time expressing themselves to others. They can, however, be taught routines and basic self-care skills and need supervised care such as in a group home.
- Profound intellectual disability (IQ below 25) is the most severe form of intellectual disability. The affected person needs to be supervised all the time. They fail to learn even the most basic self-care and communication skills. They may have very basic nonverbal communication skills. Intellectual disability may make them practically immobile, and they are quite likely to develop chronic medical conditions.
- Many individuals with intellectual disabilities are only mildly affected (IQ: 50 to 75). Such individuals with mild intellectual disability can function independently in society. They can learn how to look after themselves and survive and function in society and may have no obvious signs of intellectual disability. Additionally, they can make social connections and learn reading and math skills up to grade levels three to six.
What is intellectual disability?
Intellectual disability (previously called mental retardation) is a type of developmental disability that impairs a person’s cognitive (relating to reasoning, problem-solving, memory, and thinking) and adaptive (related to communication, self-care, and other skills required to function and live in society) skills.
The American Association of Intellectual and Developmental Disabilities classifies a condition as an intellectual disability if it meets these three criteria:
- Limitations in intellectual functioning (IQ score lower than 70 to 75)
- Behavioral limitations in adapting to environmental needs (having a conversation, using a smartphone, ability to follow rules or laws, etc.)
- Early age onset (before 22 years)
The affected child may find it hard to look after themselves or communicate their needs. Their development appears more restricted and slower than other children of their age.
Intellectual disability may vary in severity, but it invariably starts at an early age, even before the child is born.
What causes intellectual disabilities?
Many people with intellectual disabilities may not have an identifiable cause.
Intellectual disabilities can be due to several causes such as:
- Inherited conditions such as fragile X syndrome and Down syndrome
- Injury to the head during early childhood or delivery
- Infections such as meningitis, whooping cough, and measles during childhood
- Intrauterine exposure to toxic substances such as mercury, alcohol, cocaine, and certain medications
- Certain developmental abnormalities of the brain
- Metabolic conditions such as raised bilirubin levels (hyperbilirubinemia)
- Maternal alcohol syndrome
- TORCH (Toxoplasmosis, Other agents, Rubella, Cytomegalovirus, and Herpes simplex) infections in the mother during pregnancy.
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