magnus919_agent-skills/dsm5/references/10-neurodevelopmental-intellectual-developmental-disorders.md

Intellectual Developmental Disorders — Neurodevelopmental Disorders Chapter Reference

Part of the neurodevelopmental disorders chapter reference — index: 10-neurodevelopmental-disorders.md

Summarized and paraphrased from DSM-5-TR (American Psychiatric Association, 2022). This file is for orientation and education; verify exact criteria wording, codes, and recording procedures against the official DSM-5-TR before any formal clinical, legal, insurance, or research use.

Intellectual Developmental Disorder (Intellectual Disability)

Core features

A disorder with onset during the developmental period that includes deficits in BOTH intellectual functioning and adaptive functioning in conceptual, social, and practical domains. "Intellectual disability" is the term in common use by educational professions, advocacy groups, and the lay public; "intellectual developmental disorder" aligns with ICD-11 ("disorders of intellectual development"). In the United States, Rosa's Law (Public Law 111-256) replaced "mental retardation" in federal law with "intellectual disability." The condition is heterogeneous, with many genetic and nongenetic causes.

Diagnostic criteria (summarized)

• Criterion A: Deficits in intellectual functions — reasoning, problem solving, planning, abstract thinking, judgment, academic learning, and learning from experience — confirmed by BOTH clinical assessment AND individualized, standardized intelligence testing. On tests with a mean of 100 and SD of 15, this is approximately two SD or more below the population mean including a measurement error margin (generally ±5 points), i.e., a score of 65–75 (70 ± 5).
• Criterion B: Deficits in adaptive functioning that result in failure to meet developmental and sociocultural standards for personal independence and social responsibility. Without ongoing support, the deficits limit functioning in one or more activities of daily life (communication, social participation, independent living) across multiple environments (home, school, work, community). Met when at least one adaptive domain — conceptual, social, or practical — is sufficiently impaired that ongoing support is needed across environments.
• Criterion C: Onset of the intellectual and adaptive deficits during the developmental period (childhood or adolescence).
• Exclusions/rule-outs: A diagnosis must not be assumed because of a particular genetic or medical condition; criteria A–C must be met. IQ alone is insufficient — clinical judgment is required, and adaptive functioning determines needed supports.

Specifiers and severity

Severity (F70 mild, F71 moderate, F72 severe, F73 profound) is defined on the basis of ADAPTIVE functioning, not IQ scores (IQ measures are less valid at the lower end). The DSM-5-TR Table 1 describes each level across three domains:

• Mild: Conceptual — school-age children/adults have difficulties with academic skills (reading, writing, arithmetic, time, money) needing support; adult abstract thinking, executive function, and short-term memory impaired. Social — immature social interactions, difficulty reading peers' social cues, concrete/immature communication, limited risk understanding, gullibility (risk of manipulation). Practical — age-appropriate personal care; support needed for complex daily tasks (shopping, transportation, banking); support for health and legal decisions.
• Moderate: Conceptual — skills lag markedly behind peers; academic development typically at an elementary level; ongoing daily assistance needed. Social — spoken language much less complex than peers'; relationships with family/friends and sometimes romantic relations; caretakers assist with life decisions. Practical — personal care achievable with extended teaching; independent employment in jobs requiring limited conceptual/communication skills possible with considerable support; maladaptive behavior in a significant minority.
• Severe: Conceptual — little understanding of written language or concepts of numbers, quantity, time, money; caretakers provide extensive problem-solving support. Social — quite limited spoken language (single words/phrases, often augmentative); language focused on the here-and-now; understands simple speech and gestures. Practical — support needed for all daily activities and supervision at all times; maladaptive behavior, including self-injury, in a significant minority.
• Profound: Conceptual — skills generally involve the physical world rather than symbolic processes; co-occurring motor/sensory impairments may prevent functional object use. Social — very limited understanding of symbolic communication; desires expressed largely through nonverbal, nonsymbolic communication; enjoys relationships with known family/caretakers. Practical — dependent on others for all aspects of daily physical care, health, and safety; maladaptive behavior in a significant minority.

Onset, prevalence, course

• Onset: Developmental period. Delayed motor, language, and social milestones may be identifiable within the first 2 years in more severe forms; mild forms may not be identifiable until school age. Onset may be abrupt in acquired forms (meningitis, encephalitis, head trauma in the developmental period). Children under 5 who will eventually meet criteria often first meet criteria for global developmental delay.
• Prevalence: Approximately 10 per 1,000 in the general population; about 16 per 1,000 in middle-income and 9 per 1,000 in high-income countries; higher in youth than adults. In the United States, prevalence does not vary significantly by ethnoracial group.
• Course: Generally lifelong and nonprogressive, though severity levels may change over time. Some genetic disorders show worsening then stabilization (Rett syndrome) or progressive worsening (Sanfilippo syndrome, Down syndrome). Persons with Down syndrome are at high risk for neurocognitive disorder due to Alzheimer's disease in adulthood — both diagnoses are then given. Early/ongoing intervention can improve adaptive functioning, sometimes enough that the diagnosis no longer applies; assessment must determine whether improvement reflects stable generalized skill acquisition or is contingent on ongoing supports.

Risk and prognostic factors

• Genetic and physiological (prenatal): Genetic syndromes (sequence variants, copy number variants, chromosomal disorders), inborn errors of metabolism, brain malformations, maternal disease (including placental disease), and environmental influences (alcohol, other drugs, toxins, teratogens).
• Perinatal: Labor- and delivery-related events leading to neonatal encephalopathy.
• Postnatal: Hypoxic-ischemic injury, traumatic brain injury, infections, demyelinating disorders, seizure disorders (e.g., infantile spasms), severe and chronic social deprivation, and toxic metabolic syndromes/intoxications (e.g., lead, mercury).
• Course: Influenced by underlying medical/genetic conditions and co-occurring conditions (e.g., hearing or visual impairments, epilepsy).

Differential diagnosis

• Major and mild neurocognitive disorders: Characterized by LOSS of cognitive functioning rather than developmental deficits; both diagnoses can be given when IDD is present and a neurocognitive disorder develops (see 26-neurocognitive-disorders.md).
• Communication disorders and specific learning disorder: Circumscribed to communication or learning domains without global intellectual/adaptive deficits; both diagnoses are made if full criteria are also met for IDD.
• Autism spectrum disorder: IDD is common in ASD; ASD's social-communication and behavior deficits may complicate intellectual assessment, and IQ in ASD may be unstable in early childhood, so reassessment across development is essential.

Comorbidity

Rates of co-occurring mental disorders, cerebral palsy, and epilepsy are three to four times higher than in the general population. Most common co-occurring conditions: ADHD; depressive and bipolar disorders; anxiety disorders; ASD; stereotypic movement disorder (with or without self-injury); impulse-control disorders; and major neurocognitive disorder. Self-injurious behavior warrants prompt attention and may justify a separate diagnosis of stereotypic movement disorder. Aggression and disruptive behavior may occur, especially in more severe IDD. Individuals with IDD disproportionately have more health problems, including obesity, and often cannot verbalize physical symptoms, so medical illness frequently goes undiagnosed.

Assessment considerations

• Comprehensive evaluation: intellectual capacity and adaptive functioning; genetic and nongenetic etiologies; associated medical conditions (cerebral palsy, seizure disorder); and co-occurring mental, emotional, and behavioral disorders. Components may include pre-/perinatal history, three-generational pedigree, physical examination, genetic evaluation (karyotype, chromosomal microarray), metabolic screening, and neuroimaging.
• Instruments must be normed for the individual's sociocultural background and native language; brief screening tests, group tests, and highly discrepant subtest scores can invalidate an overall IQ. Consider practice effects and the "Flynn effect"; cross-battery profiles are more useful than a single IQ score.
• Adaptive functioning is assessed with clinical evaluation plus individualized, culturally appropriate, psychometrically sound measures completed by knowledgeable informants (parent, teacher, counselor, care provider). When standardized testing is impossible (sensory impairment, severe problem behavior), unspecified intellectual developmental disorder is used. In controlled settings (e.g., prisons), obtain corroborative information from outside those settings.
• Cultural sensitivity required: consider socioeconomic, ethnic, cultural, and linguistic background; cultural beliefs about causation can cause shame and underreporting. Sex ratios: males more often diagnosed (mild ~1.6:1, severe ~1.2:1).
• Suicide risk: Elevated with comorbid mental disorder, higher intellectual and adaptive function, and immediate past stressors; comorbid mental disorder may manifest atypically, so screen for suicidal thoughts and attend to behavioral change. Note associated risks of increased accidental injury (poor risk awareness) and exploitation/gullibility (relevant in criminal and Atkins-type cases).

Conversation guide

For clinicians / practitioners

• Confirm deficits in BOTH intellectual (standardized testing) and adaptive functioning; never diagnose on IQ alone. Ask informants about everyday functioning across the conceptual, social, and practical domains. Distinguish from neurocognitive disorder (decline) and from communication/SLD (circumscribed deficits); reassess after intervention in young children and across development in ASD. Screen for ADHD, mood/anxiety disorders, ASD, stereotypic movement disorder (especially with self-injury), epilepsy, and cerebral palsy; screen for suicidal thoughts. Consider etiology (pedigree, genetic testing, metabolic screening) and record the genetic syndrome as a concurrent diagnosis.

For patients and family members

• Intellectual developmental disorder (intellectual disability) means a person has significant, early-onset difficulty with learning, reasoning, and everyday practical skills. It is not a measure of worth, and with the right supports many people live full, active lives. Only qualified professionals can diagnose it, using standardized testing plus history. Ask: "What testing was used, and what does it show about strengths and support needs?", "What supports and therapies help most at home, school, and work?", and "What other conditions should we watch for?" Do not assume a genetic finding alone determines potential, that behavioral problems mean "bad behavior" (they often reflect communication difficulty, pain, or mental illness), or that improvement with good teaching means the diagnosis was wrong.

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Global Developmental Delay

Core features

A diagnosis reserved for individuals UNDER age 5 when clinical severity cannot yet be reliably assessed. It is used when an individual fails to meet expected developmental milestones in several areas of intellectual functioning and cannot undergo systematic assessment of intellectual functioning — including children too young for standardized testing.

Diagnostic criteria (summarized)

• Failure to meet expected developmental milestones in several areas of intellectual functioning, in a child under age 5 who cannot yet undergo systematic assessment (severity cannot be reliably assessed).
• Requires reassessment after a period of time; some children later meet criteria for intellectual developmental disorder.

Specifiers and severity

• No severity specifier (severity cannot be reliably assessed in this age range).

Onset, prevalence, course

• Onset by definition before age 5; course depends on underlying etiology; the diagnosis is a placeholder pending reliable assessment, and reassessment is mandatory.

Risk and prognostic factors

• Same etiologic spectrum as intellectual developmental disorder; early intervention may change the trajectory, which is why reassessment is required.

Differential diagnosis

• Intellectual developmental disorder: Definitive diagnosis deferred until systematic assessment is possible.
• Communication disorders and ASD: Global delay involves multiple domains of intellectual functioning, not a circumscribed deficit.
• Hearing/vision impairment and neurological conditions should be excluded.

Comorbidity

• Delays in multiple developmental domains frequently co-occur with the same medical/genetic conditions that cause intellectual disability.

Assessment considerations

• With standardized intellectual assessment not feasible, use milestone history, informant report, direct observation, and developmental tools; rule out sensory impairment; plan a formal reassessment window.

Conversation guide

For clinicians / practitioners

• Do not over-diagnose from a single delay — "global" requires several areas to be affected. Investigate medical/genetic causes early (hearing, vision, neurology, genetics) because some are treatable, and set a documented reassessment plan.

For patients and family members

• Global developmental delay means your young child is not yet meeting expected milestones in several areas of learning and development and will be re-evaluated later. It is an early "let's help now and keep watching" label, not a final verdict. Ask: "What can we do now at home and in early intervention?", "What medical tests should we consider?", and "When will we reassess?" Do not assume the delay is permanent or that it means a specific diagnosis.

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Unspecified Intellectual Developmental Disorder (Intellectual Disability)

Core features

Reserved for individuals OVER age 5 when assessment of the degree of intellectual developmental disorder by locally available procedures is rendered difficult or impossible because of associated sensory or physical impairments (e.g., blindness or prelingual deafness), locomotor disability, or severe problem behaviors or co-occurring mental disorder.

Diagnostic criteria (summarized)

• Symptoms characteristic of IDD with impairment, but the degree of intellectual disability cannot be quantified with locally available procedures for the reasons above.
• Used only in exceptional circumstances; requires reassessment after a period of time.

Specifiers and severity

• No severity specifier is assigned (severity cannot be reliably assessed).

Onset, prevalence, course

• Onset in the developmental period; used for individuals over age 5 when IDD is present but unquantifiable.

Risk and prognostic factors

• Same etiologic spectrum as IDD; inability to test usually reflects co-occurring sensory, motor, or behavioral factors.

Differential diagnosis

• IDD with specified severity: used when reliable assessment is possible.
• Neurocognitive disorders: distinguished by developmental-period onset and absence of decline from a prior level (see 26-neurocognitive-disorders.md).

Comorbidity

• Severe sensory/physical impairments, severe problem behaviors, and co-occurring mental disorders are the reasons this category is used; each should be managed and treated.

Assessment considerations

• Attempt the best available assessment with accommodations (nonverbal measures, adapted administration); document why standardized testing was impossible; plan reassessment.

Conversation guide

For clinicians / practitioners

• Use sparingly, only when testing is genuinely impossible; document the reason, set a reassessment plan, and consider adapted instruments and specialist consultation.

For patients and family members

• When standard intellectual assessment is not possible (e.g., because of a sensory impairment), clinicians may use a broad label while gathering information. Ask what alternative ways of assessing learning and daily skills exist and what the reassessment plan is. Do not assume that inability to take a standard test means a person's abilities are permanently unknown.

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