Mild intellectual disability is a form of intellectual disability. It affects a person's intellectual abilities and adaptation skills to a mild extent. Mild intellectual disability is also called mild ID or mild intellectual developmental disorder, and was formerly called mild mental retardation. Mild ID affects about 1% of the population worldwide and is often inherited. It can also be caused by environmental factors and by other medical conditions and disorders (such as Down syndrome). Many children with mild ID seem like they are developing typically until they start school. In school, children with mild ID often learn more slowly than their peers and may have trouble memorizing facts and thinking abstractly. Children with mild ID may also have delayed social skills and often need assistance with activities of daily living. Adults with mild ID usually have academic abilities similar to a typically-developing person who has gone to school for 7-8 years. Many adults with mild ID can work and live alone. However, they may need help with more complex activities of daily living, including preparing food, managing their money, and organizing social events. Mild ID is comorbid with many disorders, particularly developmental disorders. Disorders that are comorbid with mild ID include attention-deficit/hyperactivity disorder, autism spectrum disorder, developmental coordination disorder, and cerebral palsy.
Signs and symptoms
In early childhood, children with mild ID may develop similarly to typical children. They can usually understand concepts such as time, distance, money, and avoiding danger. However, they often struggle with memorizing things like the days of the week or phone numbers. They may need help understanding theory of mind, but can usually be polite to other people and play with other children. They generally also need support in activities of daily living including brushing their teeth, using the toilet, and taking a bath.
School-aged children and teenagers with mild ID often struggle to solve abstract problems. They may take longer than their peers to understand arithmetic, reading, and writing. They may also have difficulty maintaining sustained attention for longer than 30 minutes. Children and adolescents with mild ID often understand social situations in a more concrete way than most of their peers. They may need support to understand social cues or initiate conversation. By this age, most people with mild ID will be able to complete most activities of daily living on their own.
Adults with mild ID usually have academic skills similar to a typical person who has gone to school for 7-8 years. Mildly intellectually disabled adults may struggle with executive functioning. They may have trouble with complex activities of daily living, such as managing their money, preparing their own food, and shopping. Many adults with mild ID can work and live alone. Some can even raise a family with support from other people. People with mild ID have similar recreational habits to people with normal intelligence. Adults with mild ID may have trouble regulating their emotions and behavior in conversations. In social situations, they may act younger than their age. They also have a higher risk of being manipulated by their peers.
Many people with mild ID have an IQ between 55 and 70. However, the Diagnostic and Statistical Manual of Mental Disorders (DSM) states that someone should be diagnosed with a level of intellectual disability, such as "mild", based on their ability to adapt, not based on their IQ test scores.
Causes
A specific biological cause of intellectual disability is less likely to be found for people with mild intellectual disability than for people with more severe forms of intellectual disability. Mild ID is also more likely to be inherited than other forms of ID, which often come from de novo mutations. About 21% of cases of mild ID are caused by small genetic errors called genetic microdeletions and duplications. The prevalence of mild ID varies between different populations based on environmental factors, such as access to education and access to healthcare. More severe forms of ID have the same prevalence in most different places. Mild ID is also more less likely to be caused by another medical condition than more severe forms of ID.
A girl with Down syndrome competing at a gymnastics competition in Chesterland, Ohio. Down syndrome is commonly comorbid with mild ID.
Mild ID can also be caused by another medical condition. About 20-50% of adults with Down syndrome (DS) have mild intellectual disability. People with DS usually have milder levels of intellectual disability if they are female, do not have epilepsy, and have lower levels of a protein called C-reactive protein. Young children with DS are also more likely to have mild ID than adolescents with DS. Other genetic disorders can also lead to mild ID. For example, most children with Williams syndrome also have mild ID. Microcephaly is also considered a risk factor for mild ID. One study found that 14.7% of children withdevelopmental disabilities and microcephaly had mild ID, while only 9.5% of children with developmental disabilities and normal skull size had mild ID.
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