Markers of intellect include problem solving, reasoning, logical and abstract reasoning, planning, learning from experience, etc. Intellectual Disability(ID) is deficits in these markers of intellect.
Intelligence is measured using standardized intelligence tests. These tests result in Intelligence Quotient (IQ) which is based on comparative data from the entire population for which the test is valid.
There are levels of severity of ID. Normally, IQ below 70-75 qualifies for the diagnosis of ID. However, IQ is not the sole marker of ID. As IQ lowers, validity decreases.
Hence, adaptive functioning is used as the marker for severity of ID as it determines the quality of support required for functioning. Levels of severity include Mild, Moderate, Severe and Profound.
There are numerous causes of ID including genetic and psychosocial influences. Genetic causes include Down Syndrome, Lesch-Nyhan syndrome, Fragile X syndrome. High levels of phenylketonuria (PKU) is also associated with development of seizures causing ID.
Environmental neglect, abusive parenting, malnutrition coupled with biological influences, traumatic brain injuries, delivery related accidents, hypoxia may lead to development of ID.
Common Signs and Symptoms
DSM-5 characterises intellectual deficits in three domains: conceptual, social and practical. Conceptual deficits include difficulties in areas such as language, reasoning, knowledge and memory.
Social deficits include problems in social judgement and ability to make and retain friendships. Practical deficits are difficulties managing job responsibilities and personal care.
Common signs include:
- Slow or lack of developmental milestones such as language skills, toilet training, self help, etc.
- Continued infant-like behaviour
- Failure to adjust to new situations
- Academic problems or lagging behind in school
- Difficulty understanding and following social rules
These difficulties may range from mild to severe.
Various genetic syndromes such as fragile X syndrome, fetal alcohol syndrome, down syndrome, etc. Brain malformations, inborn errors in metabolism, traumatic brain injury are all related to Intellectual Disability.
Delivery related complications causing encephalopathy, seizure disorders, hypoxic ischemic injury, mercury or lead intoxications, etc may cause ID. Intake of drugs and alcohol by the mother also affects brain chemistry in children.
DSM-5 lists the following criteria for the diagnosis of ID:
- Deficits in intellectual functioning such as difficulty with reasoning, problem solving, planning, judgement, abstract thinking, learning from experience, etc.
- Adaptive functioning deficits displayed through result failure to meet developmental and sociocultural standards for personal and social responsibility. Limited functioning in one or more activities of daily life, such as communication, social participation, and independent living, across multiple environments, such as home, school and work.
A developmental psychologist, child psychologist or a clinical psychologist is able to diagnose ID with the help of clinical assessment and standardised intelligence testing. They are required to note the severity of the disability.
There is no cure for ID. The basic goal for treatment of ID is to help them learn to take care of themselves and be responsible members of the society, be able to read and write and hold jobs. But the outcomes vary depending on the severity of the disability.
In case of mild and moderate ID, treatment is often along the lines of helping them learn and adapt to take care of themselves, hold a job and learn to read and write. In case of severe and profound ID, they often need more supportive care and the goal is to identify their needs and help them with their day to day activities.
A developmental child psychologist or a clinical psychologist often provides the diagnosis and the treatment for ID.