Alzheimer’s disease, or an individual with intellectual disability who loses further cogni- tive capacity following a head injury). In such cases, the diagnoses of intellectual disability and neurocognitive disorder may both be given.
Communication disorders and specific learning disorder. These neurodevelopmental disorders are specific to the communication and learning domains and do not show defi- cits in intellectual and adaptive behavior. They may co-occur with intellectual disability.
Both diagnoses are made if full criteria are met for intellectual disability and a communi- cation disorder or specific learning disorder.
Autism Spectrum disorder. Intellectual disability is common among individuals with autism spectrum disorder. Assessment of intellectual ability may be complicated by so- cial-communication and behavior deficits inherent to autism spectrum disorder, which may interfere with understanding and complying with test procedures. Appropriate as- sessment of intellectual functioning in autism spectrum disorder is essential, with reas- sessment across the developmental period, because IQ scores in autism spectrum disorder may be unstable, particularly in early childhood.
Co-occurring mental, neurodevelopmental, medical, and physical conditions are frequent in intellectual disability, with rates of some conditions (e.g., mental disorders, cerebral palsy, and epilepsy) three to four times higher than in the general population. The prognosis and outcome of co-occurring diagnoses may be inﬂuenced by the presence of intellectual disability. Assessment procedures may require modifications because of associated disor- ders, including communication disorders, autism spectrum disorder, and motor, sensory, or other disorders. Knowledgeable informants are essential for identifying symptoms such as irritability, mood dysregulation, aggression, eating problems, and sleep problems, and for assessing adaptive functioning in various community settings.
The most common co-occurring mental and neurodevelopmental disorders are atten- behavior); impulse-control disorders; and major neurocognitive disorder. Major depres- sive disorder may occur throughout the range of severity of intellectual disability. Self- agnosis of stereotypic movement disorder. Individuals with intellectual disability, partic- ularly those with more severe intellectual disability, may also exhibit aggression and disruptive behaviors, including harm of others or property destruction.
Relationship to Other Classifications
ICD-ll (in development at the time of this publication) uses the term intellectual develop- mental disorders to indicate that these are disorders that involve impaired brain functioning early in life. These disorders are described in ICD-11 as a metasyndrome occurring in the developmental period analogous to dementia or neurocognitive disorder in later life.
There are four subtypes in ICD-ll: mild, moderate, severe, and profound.
The American Association on Intellectual and Developmental Disabilities (AAIDD) also uses the term intellectual disability with a similar meaning to the term as used in this manual. The AAIDD’s classification is multidimensional rather than categorical and is based on the disability construct. Rather than listing specifiers as is done in DSM-5, the
AAIDD emphasizes a profile of supports based on severity.
315.8 (F88)
This diagnosis is reserved for individuals under the age of 5 years when the clinical severity level cannot be reliably assessed during early childhood. This category is diagnosed when an individual fails to meet expected developmental milestones in several areas of intellec- tual functioning, and applies to individuals who are unable to undergo systematic assess- ments of intellectual functioning, including children who are too young to participate in standardized testing. This category requires reassessment after a period of time.
This category is reserved for individuals over the age of 5 years when assessment of the degree of intellectual disability (intellectual developmental disorder) by means of locally available procedures is rendered difficult or impossible because of associated sensory or physical impairments, as in blindness or prelingual deafness; locomotor disability; or pres- ence of severe problem behaviors or co-occurring mental disorder. This category should only be used in exceptional circumstances and requires reassessment after a period of time.