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Man with intellectual disability at desk colouring and writing
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Mild intellectual disability

A complete overview of Mild intellectual disability, answering frequently asked questions about this diagnosis, provided by Elisabeth Fernell and Ida Lindblad.

Definition

Mild intellectual disability (previously known as mild mental retardation) refers to deficits in intellectual functions pertaining to abstract/theoretical thinking. Mild intellectual disability occurs in approximately 1.5 percent of the population. Other cognitive functions are usually affected as well, which leads to deficits/disorders in other areas. For example, people with mild intellectual disability also often meet the criteria for ADHD. Intellectual disability affects adaptive functioning, i.e. the skills needed to navigate everyday life, which calls for tailored support. This in turn means that follow-up of individuals with intellectual disability must assess not only their cognitive and intellectual functions but also their need for support.

Authors

Ida Lindblad & Elisabeth Fernell

Prevalence

Prevalence studies in various geographic and demographic areas have shown that approximately 0.5-1.5 percent of the population meet criteria for mild intellectual disability. Studies show major variation in the prevalence of mild intellectual disability, depending on which definition has been used and the demographic and socioeconomic factors of the studied area.

Causes

In all neurodevelopmental disorders, possible or certain causes can be categorised according to when the brain injury/disorder originally arose. There is usually a distinction between the prenatal period (the period before birth), the perinatal period (the first week, including the birth itself) and the postnatal period, where the injury/disorder occurred after the perinatal period. Genetic factors dominate among prenatal causes and include both inherited conditions and de novo (new) mutations. This group includes a large number of known syndromes. The term syndrome refers to several simultaneously occurring and clinically observable signs or symptoms that collectively indicate an underlying medical condition.

As with other neurodevelopmental disorders, medical causes of intellectual disability can usually be traced to the prenatal period. However, there are many children with mild intellectual disability for whom we cannot define the exact medical cause. The underlying medical cause is much more frequently identified for children with more severe forms of intellectual disability.

Various genetic/chromosomal syndromes can cause mild intellectual disability, for example DiGeorge syndrome and Klinefelter syndrome (boys with XXY chromosomes). Thanks to CGH (comparative genomic hybridisation) arrays, capable of detecting very small genetic abnormalities (like deletions and duplications), genetic diagnostics have improved even further. One study was able to identify such a genetic abnormality as the underlying cause in 21% of children with mild intellectual disability.

Given the current rate of development in genetic testing, we will be able to map out more and more causes in the future. Among acquired prenatal causes, foetal alcohol spectrum disorder (FASD) is the most widely known. Perinatal causes can be related to risks associated with the immature brain, i.e. if the child is born very or even extremely prematurely (earlier than 32 weeks or 27-28 weeks, respectively).

Mild intellectual disability can sometimes also be an expression of the variation in human abilities and aptitude relative to society’s demands.

Diagnosis

According to DSM-5, mild intellectual disability is defined by three criteria (A-C):

Intellectual functioning is assessed by testing the individual’s cognitive functions using standardised psychometric test instruments. Common assessment tools include Leiter, the Wechsler scales, and Snijders-Oomen (SON-R). The Wechsler scales are most frequently used, but some cases might require non-verbal tests like Leiter and SON-R.

Adaptive functioning is assessed by collecting information about the child’s development and functioning from parents/guardians, child health care services and school (including school health care services) and – in the case of adults – other loved ones. Adaptive functioning encompasses skills needed in everyday life, so part of the assessment involves determining how much support the patient requires. Scoring scales are often used to supplement and solidify the assessment process, and in such cases the Vineland Adaptive Behaviour Scales or ABAS (Adaptive Behaviour Assessment Scales) are the ones most commonly used.

Any diagnosis of intellectual disability ultimately hinges on these three criteria. One must also determine whether the cognitive and adaptive deficits might be due to some other disorder, for example major attention deficits or language difficulties, rather than the result of intellectual disability.

Diagnosing intellectual disability is crucial not only to inform and educate the child and their parents/guardians about what the disorder entails, but also in order to give them access to whatever supportive measures the school and society at large can provide.

If the assessment is inconclusive, the individual is followed up with psychological assessment and renewed medical examination after about a year.

Symptoms

Mild intellectual disability involves deficits in theoretical thinking/learning. This means that the person perceives their surroundings in a more concrete manner, making it harder to interpret and deal with e.g. abstract words, symbols and descriptions. This hinders their learning, especially their ability to absorb theoretical (as opposed to more practical) knowledge, which in turn makes things more difficult at school.

The deficits in theoretical/abstract thinking affect adaptive functioning, so most people with mild intellectual disability need support all their lives just to get by in everyday life. Adapting to your environment and the demands of adult life like managing your job, home and finances can be a major challenge. Adaptive functioning is usually divided into three domains: cognitive, social and practical. Reading, writing, arithmetic and concepts like time and money all rely on cognitive functioning. Deficits in social functioning make it hard to navigate social relationships in an age-appropriate manner, due to impaired communication skills, difficulties understanding signals from peers and poor social judgment that might lead to manipulation by others (gullibility). Limitations in practical functioning lead to an inability to handle daily routines, taking care of a household and making decisions about legal and health-related issues – in other words, the kind of things that everyday life requires. DSM-5 specifies that support is needed in the event of parenting children.

Concurrent cognitive difficulties/disorders

Concurrent cognitive difficulties are common among individuals with mild intellectual disability. These difficulties often relate to concentration, motor control, language/communication, social interaction, sight and hearing, and present additional problems that need to be recognised. All individuals should be examined from a comprehensive ESSENCE perspective, taking any co-existing difficulties into account. Moreover, every examination process must also remember to consider the fact that children with other disorders like cerebral palsy or epilepsy might also have intellectual disability.

Intervention/support and follow-up

After the examination process is complete and mild intellectual disability has been diagnosed, the patient is entitled to support from habilitation services. Follow-up information about the diagnosis is crucial in this context, because it helps the individual understand the difficulties they face and the support they need. This includes information about parenthood and what that entails when an intellectual disability is involved.

Individuals diagnosed with intellectual disability are also entitled to support through The Swedish Act Concerning Support and Service for Persons with Certain Functional Impairments (LSS). This includes access to a contact person, short stays away from home and short periods of supervision for schoolchildren over 12 years of age. Adults can get assistance in daily activities or be offered a residence with special services (or other specially adapted housing).

The school must also take appropriate measures by providing the person with support and tailored efforts. Individuals with intellectual disability are entitled to a tailored curriculum – the special school curriculum. In some cases, the special school curriculum can be implemented in a regular school environment, but it is usually only taught in special schools.

If a child is diagnosed with mild intellectual disability, it is very important to monitor their development and perform follow-up examinations as necessary.