Intellectual disability’s DSM-5 debut

The newest and fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, the DSM-5, makes an important change in terminology — from mental retardation to intellectual disability — for those with intellectual impairments.

But more important is the DSM-5’s greater reliance on adaptive functioning, defined as intellectual function in daily life, or the capacity to function independently and with a sense of social responsibility — for example, understanding time and the value of money; perception and interpretation of social cues; and care for personal needs such as eating and dressing.

The DSM-5 relies more on adaptive functioning than the DSM-IV did,both for diagnosing intellectual disability and for determining its level of severity.

In terms of diagnosis, the DSM-5 requires at least one domain that includes several skill areas of adaptive functioning versus two or more skill areas in the DSM-IV. The DSM-5 also describes a new social domain that has important consequences for individuals with autism.

An individual who needs ongoing support in social adaptive functioning, without necessarily having any impairment in conceptual or practical adaptive functioning, could be diagnosed as having intellectual disability if deficits in general mental abilities are also present.

For instance, an individual who uses spoken language for social communication in a simpler way than peers do, but has difficulties interpreting social cues, may be diagnosed with autism. If the individual also shows problems with reasoning, problem-solving, abstract thinking and learning at school (deficit in intellectual functioning), a clinician would alsomake a diagnosis of intellectual disability.

The DSM-5 recommends applying clinical judgment to interpret tests of intelligence quotients (IQ), rather than relying exclusively on IQ scores, for assessing deficits in intellectual functions. This may result in an individual with an IQ of 80 to 85 and autism spectrum disorder being diagnosed with both intellectual disability and autism spectrum disorder. Under the DSM-IV, however, this individual would have only been diagnosed with autism.

In this case, clinical judgment would advise labeling this individual as having mild intellectual disability (based on IQ), rather than a more severe level, even if his or her social functioning impairment is substantial.

The DSM-5 also describes the types of deficits in the social domain to be considered (such as level of language or communication skills), which may help to not overemphasize social deficits in determining the severity of intellectual disability.

There are other features of the revised diagnostic criteria for intellectual disability — for example, referring to “the developmental period” rather than a specific age of onset — that may have fewer consequences for individuals with autism.

Overall, under the DSM-5, more people with autism spectrum disorder, particularly those with borderline intellectual functioning, are likely to be diagnosed with both intellectual disability and autism spectrum disorder.

Walter Kaufmann is director of the Rett Syndrome Program at Boston Children’s Hospital and a member of the DSM-5 Neurodevelopmental Disorders Work Group.