What causes intellectual disability?
Intellectual disability can arise when genetic variation, disruptions of prenatal brain development, complications around birth, or injuries and diseases during childhood affect the development of intellectual and adaptive functioning. Some people have a single identifiable genetic or medical condition. Others have several interacting contributors, and in many cases the precise cause remains unknown even after a careful evaluation. The timing, mechanism, and strength of evidence matter: a confirmed disease-causing genetic change is different from a factor associated with elevated population risk, and neither automatically predicts one person's intellectual abilities or future support needs. The American Academy of Pediatrics (AAP) describes this etiologic diversity in its 2025 clinical report on developmental delay and intellectual disability (Rodan et al., 2025).
Intellectual disability itself is defined by significant limitations in intellectual functioning and adaptive behavior beginning during development. Learning, reasoning, and problem-solving are considered alongside conceptual, social, and practical everyday skills. The American Association on Intellectual and Developmental Disabilities (AAIDD) places onset before age 22 in its current operational definition; diagnostic manuals may apply their own developmental-period formulations. The cause of a person's condition and the clinical determination that the person meets criteria for intellectual disability are separate questions (AAIDD, Defining Criteria).
The major categories of causes are chromosomal and single-gene conditions; prenatal infections, toxic exposures, and disruptions of fetal development; certain perinatal and neonatal brain injuries; metabolic, infectious, toxic, and traumatic conditions acquired during development; and combinations of inherited susceptibilities and environmental exposures. Research increasingly identifies molecular explanations, while clinical history and developmental assessment remain indispensable. Etiology may guide medical surveillance and family counseling, but functional assessment determines the supports that make daily participation possible.
Etiology, risk factors, and the meaning of a diagnosis
A cause is more specific than a statistical association
A cause is an event, condition, or mechanism supported by evidence as producing or materially contributing to a developmental outcome. A risk factor identifies a higher probability in a population. For example, a pathogenic variant known to disrupt a crucial neurodevelopmental protein may strongly establish an etiologic diagnosis. Preterm birth, considered alone, describes an increased risk across groups and does not prove that a particular child's developmental difficulties arose from prematurity. Both forms of evidence are useful when interpreted at the right level.
Population studies cannot necessarily separate biological pathways from other correlated influences. Maternal medical illness, prematurity, birth weight, access to healthcare, and socioeconomic conditions may be linked to one another. A 2016 meta-analysis found associations between several prenatal, perinatal, and neonatal characteristics and later intellectual disability, but the underlying studies were observational and often heterogeneous. Some examined social categories that are proxies for structural conditions rather than biologically causal traits. Their associations must not be converted into judgments about individual families (Huang et al., 2016).
Intellectual disability differs from other developmental outcomes
A genetic syndrome may be associated with intellectual disability in some people and with other neurodevelopmental differences in others. Language delay, autism, hearing loss, learning disorders, epilepsy, and cerebral palsy can coexist with intellectual disability, but none is synonymous with it. Likewise, a low test score influenced by inaccessible communication, sensory impairment, language unfamiliarity, or insufficient educational opportunity does not establish intellectual disability on its own. Evaluation requires standardized intellectual and adaptive assessment interpreted in developmental, linguistic, cultural, and clinical context (AAIDD, Defining Criteria; Rodan et al., 2025).
For younger children, clinicians may use the diagnosis of global developmental delay when multiple developmental domains are affected and a reliable formal assessment of intellectual functioning is not yet feasible. Some children later meet criteria for intellectual disability; others follow different developmental trajectories. An etiologic evaluation may begin well before a stable intellectual-disability diagnosis is possible.
Genetic and chromosomal causes
Genetic causes form a large and diverse part of the explanatory landscape. The AAP clinical report distinguishes chromosomal changes, single-gene disorders, imprinting disturbances, and more complex genetic mechanisms. Many arise spontaneously during the formation of reproductive cells or early embryonic development; others are inherited through recognized transmission patterns. Finding a genetic cause does not by itself establish the degree of cognitive limitation, because clinical expression may vary among people with the same diagnosis (Rodan et al., 2025).
Chromosome number and structural changes
A chromosome can be present in an extra copy, absent, or structurally rearranged. Down syndrome, commonly caused by an additional copy of chromosome 21, is a familiar example of a chromosomal condition frequently associated with intellectual disability. Its clinical characteristics vary, and health, communication, education, and individual experience influence the functional profile. Chromosomal microdeletions and microduplications may affect multiple genes, sometimes alongside heart differences, seizures, growth changes, or distinctive physical findings. Their significance depends on the genomic region, the type of change, and its established relationship with disease.
Chromosomal microarray analysis can identify many clinically significant copy-number changes, although it is not designed to find every sequence variant, balanced rearrangement, repeat expansion, or methylation disturbance. A normal microarray result therefore does not exclude a genetic cause. Genomic testing is selected according to clinical findings and the capabilities of the laboratory platform (Rodan et al., 2025).
Single-gene conditions and molecular pathways
Rare pathogenic variants in individual genes can interfere with neuronal signaling, synapse development, gene regulation, protein synthesis, or brain growth. Some associated syndromes have recognizable patterns of movement, behavior, seizures, language development, or medical complications; others are initially identified through broad sequencing rather than a distinctive physical presentation. Fragile X syndrome, associated with an expanded CGG repeat in FMR1, is an important example whose molecular mechanism is not reliably detected by routine exome sequencing. Targeted testing can be necessary when the clinical or family history indicates it.
Molecular findings require classification. A pathogenic or likely pathogenic variant interpreted in an appropriate phenotype has a different clinical meaning from a variant of uncertain significance. A laboratory report listing an unfamiliar change is not enough to say that the change caused intellectual disability. Variant interpretation may change as research and family segregation information accumulate. A clinical genetics team can integrate inheritance, phenotype, disease mechanism, and the laboratory's technical limits (Rodan et al., 2025).
Inherited, de novo, mosaic, and imprinting mechanisms
A variant may be inherited from a parent or may be de novo, meaning it is newly detected in the child and absent from the tested parental samples. Dominant, recessive, and X-linked transmission create different recurrence patterns. Mosaicism occurs when cells within the same person do not all have an identical genetic constitution; blood testing can occasionally miss a relevant mosaic variant present predominantly in another tissue. Imprinting disorders involve parent-of-origin-specific gene expression, commonly through methylation changes or uniparental disomy. Angelman syndrome and Prader–Willi syndrome illustrate why an etiologic investigation sometimes needs methylation or other targeted methods, rather than sequencing alone (Rodan et al., 2025).
Recurrence counseling must follow the actual mechanism. It is scientifically inaccurate to assign the same recurrence probability to all genetic forms of intellectual disability. In particular, identifying a de novo variant may substantially change counseling compared with identifying a recessive inherited condition, yet residual risk may remain because of parental germline mosaicism. Counseling should be individualized and ideally delivered with a genetics professional.
Why genetic diagnosis matters clinically
A molecular diagnosis may clarify prognosis, identify complications to monitor, prevent a succession of low-value investigations, inform reproductive counseling, and occasionally point to a mechanism-specific treatment or trial. It can also help families connect with accurate syndrome-specific resources. At the same time, a genetic result does not replace observation of a child's developmental progress or assessment of communication, learning, and adaptive needs. Clinical management should integrate both (Manickam et al., 2021; Rodan et al., 2025).
Prenatal causes: developmental processes before birth
The fetal brain develops through interconnected stages of cell proliferation, migration, differentiation, organization, and circuit formation. Genetic programs and the prenatal environment jointly influence those processes. Some disruptions leave an identifiable malformation, infection history, or metabolic signature; others are recognized only through later developmental findings. The same prenatal event may have different consequences according to timing, severity, duration, fetal susceptibility, and accompanying conditions.
Alcohol exposure and fetal alcohol spectrum disorders
Prenatal alcohol exposure can directly disrupt fetal development. Fetal alcohol spectrum disorders (FASDs) comprise a range of outcomes affecting behavior, learning, attention, executive functioning, physical development, and, for some affected individuals, intellectual and adaptive functioning. A diagnosis within the FASD spectrum does not imply that every affected person has intellectual disability. Public health guidance states that there is no known safe amount or safe time for alcohol consumption during pregnancy (CDC, FASD; CDC, Alcohol Use During Pregnancy).
Clinical interpretation should consider documented exposure, validated diagnostic criteria, developmental observations, and alternative or coexisting explanations. A history of possible exposure alone is not an intellectual-disability diagnosis. Prevention advice and healthcare support are most effective when accessible, practical, and free of moralized assumptions about families.
Congenital infections
Certain infections acquired during pregnancy can affect fetal brain development. Congenital cytomegalovirus (CMV) can be associated with microcephaly, seizures, motor and developmental difficulties, vision impairment, and hearing loss. Many infants with congenital CMV remain well, while others develop complications, some recognized after the newborn period. Hearing loss itself can change language acquisition and test performance, making careful differential assessment essential (CDC, Congenital CMV).
Congenital rubella syndrome can produce hearing and vision loss, congenital heart differences, and intellectual disability when infection occurs during pregnancy, particularly early in gestation. Rubella vaccination programs exemplify prevention of an established infectious developmental hazard. Other infections may require targeted assessment when supported by maternal, neonatal, imaging, or neurological findings; the mere possibility of prenatal infection is insufficient to establish its involvement in a specific case (CDC, Rubella).
Nutrition, endocrine conditions, and metabolic disturbances
Adequate nutrition and maternal metabolic stability support fetal growth and nervous-system development. Severe iodine deficiency and related thyroid-hormone disturbances can impair neurodevelopment; public health nutrition and appropriate management of thyroid disease are established preventive approaches. Maternal diabetes and other medical conditions can be associated with adverse developmental outcomes, but the clinical significance depends on severity, treatment, associated complications, and additional influences. A statistical association cannot be read as evidence of an avoidable parental action in any one family.
Some inborn metabolic disorders begin affecting brain development prenatally or shortly after birth, and several are amenable to specific treatment when recognized promptly. Their clinical importance exceeds their relative frequency. A diagnostic strategy should therefore prioritize treatable or urgent conditions when symptoms and examination findings point toward them (Rodan et al., 2025).
Medications, toxicants, and prenatal exposure assessment
Certain medicines and environmental toxicants carry established fetal risks, but effects are substance-specific and depend on exposure conditions. The clinical question is the identity, timing, dose, and indication of the exposure, together with what rigorous evidence shows about developmental outcomes. Pregnant patients should consult qualified clinicians before starting, discontinuing, or changing medication; abrupt cessation of necessary treatment can itself create significant risks. Observational drug-exposure studies may be confounded by the underlying illness for which treatment was prescribed.
Prenatal brain development also depends on placental function, fetal growth, and adequate oxygen and nutrient delivery. Placental insufficiency or major vascular events may contribute to developmental injury in selected circumstances. An abnormal ultrasound finding, low birth weight, or complicated pregnancy may warrant further evaluation, but does not uniquely identify the mechanism of later intellectual disability (Rodan et al., 2025).
Perinatal and neonatal contributors
Prematurity and complications around birth
Children born very preterm, especially those who experience substantial neonatal medical complications, have higher rates of some later neurodevelopmental difficulties at the population level. Very low birth weight is also associated with increased risk. These factors are not specific causes in every individual and do not imply that intellectual disability is inevitable after preterm birth. Longitudinal studies must account for illness severity, family context, access to care, and the considerable variation in individual outcomes. Associations reported in the prenatal and neonatal literature are informative for follow-up planning but cannot substitute for case-specific investigation (Huang et al., 2016).
Hypoxic–ischemic and hemorrhagic brain injury
Severe interruption of oxygen delivery or blood flow to the developing brain can cause hypoxic–ischemic injury. Intraventricular hemorrhage, stroke, or other serious neonatal neurological complications may likewise alter developmental trajectories. Evidence that a particular event produced lasting impairment depends on contemporaneous clinical records, examination, imaging, timing, and subsequent development. A brief low Apgar score or nonspecific account of a difficult delivery is not sufficient to attribute a person's intellectual disability to birth injury.
Where major neonatal encephalopathy or brain injury is documented, follow-up should address cognition alongside movement, hearing, vision, feeding, communication, and seizures. Early recognition of medical and communication needs can alter participation and quality of life even when the original injury cannot be reversed. Genetic contributors may also coexist with an apparently acquired neurological presentation, so a birth-related history should not prematurely close diagnostic investigation (Rodan et al., 2025).
Neonatal infections and metabolic emergencies
Severe neonatal meningitis, encephalitis, uncontrolled metabolic crises, and other serious illnesses may cause brain injury during a particularly vulnerable developmental period. The possibility of a treatable metabolic disease is especially important when episodes of developmental regression, seizures, unusual movements, recurrent illness, unexplained metabolic acidosis or hypoglycemia, or distinctive multisystem findings occur. The 2025 AAP clinical report discusses targeted metabolic testing when such red flags are present. A broad list of rare disorders is less useful than a medically informed evaluation matched to the observed phenotype (Rodan et al., 2025).
Conditions and exposures acquired in childhood
Central nervous system infections, trauma, and other injuries
During childhood, severe meningitis, encephalitis, traumatic brain injury, stroke, prolonged medical crises, and certain forms of toxic exposure can interfere with ongoing cognitive and adaptive development. Etiologic reasoning must establish the onset and course of developmental difficulty. If significant limitations clearly preceded an injury, that injury cannot explain the original condition, although it may increase support needs. If a child loses previously acquired abilities or changes abruptly, clinicians must consider an acquired neurological disorder, active illness, or neurodegenerative process rather than assuming a stable developmental difference.
Lead and other neurotoxic exposures
Lead is a preventable neurotoxin that can affect children's learning, attention, and development. The CDC emphasizes that no safe blood lead level has been identified in children. Exposure control and medically guided testing are important public-health and clinical practices. Lead exposure can contribute to developmental impairment, but an individual's specific cognitive and adaptive profile cannot be explained solely by the fact that a blood lead level was once above a reference value. A detailed developmental and medical assessment remains necessary (CDC, Childhood Lead Prevention).
Environmental adversity, opportunity, and the interpretation of impairment
Adversity, chronic deprivation, unequal healthcare access, and disrupted opportunities for learning can influence developmental outcomes and the measurement of skills. Their effects may interact with biological vulnerabilities. However, poverty or a family's social circumstances cannot be treated as an automatic etiologic diagnosis, and a lack of educational opportunity may distort an intelligence test without establishing a global developmental impairment. Assessment should be culturally appropriate, include multiple sources of information, and evaluate the supports and opportunities a person has actually had. AAIDD's framework explicitly recognizes biomedical, social, behavioral, and educational risk factors operating across developmental periods (AAIDD, Interrelated Causes of IDD).
The causal distinction is clinically important. A child's difficulty performing an unfamiliar school task in a second language may reflect accessibility and instruction; limitations appearing across varied settings and domains may suggest a broader developmental condition. Both deserve attention, but they require different kinds of evidence. A valid assessment avoids reducing disability to a social category or to an isolated IQ score.
How genetic and environmental mechanisms interact
A binary division into genetic and environmental cases obscures biological reality. Genes influence the formation, maturation, and maintenance of neural systems, while developmental conditions influence how those systems function. A chromosomal disorder and a prenatal infection can coexist. A rare genetic variant may affect vulnerability to seizures or metabolic stress. A child's medical condition can shape educational access, and accessible education can improve practical and communicative skills regardless of the underlying etiology.
Several distinct claims must be kept separate. A gene–environment interaction means an environmental effect differs by genotype in a specified design; a gene–environment correlation describes an association between inherited propensities and experienced environments; epigenetic regulation refers to mechanisms controlling gene expression without changing DNA sequence. These are legitimate research constructs but are often overextended in public explanations of intellectual disability. Clinical proof of a specific causal pathway requires corresponding molecular, developmental, and epidemiologic evidence. An untested epigenetic story should not be substituted for a diagnosis.
Severity, intellectual-test profiles, and daily support needs do not map one-to-one onto any single causal category. The same condition may be accompanied by different language abilities, medical needs, family resources, and environments. Etiologic classification therefore informs the clinical formulation but does not determine educational placement, independence, legal capacity, or an individual's goals (AAIDD, Defining Criteria; Rodan et al., 2025).
How clinicians investigate the cause
Developmental history and physical examination come first
The etiologic workup begins with the pattern of development: when concerns emerged, which domains are affected, whether skills have progressed, plateaued, or regressed, and whether there are associated motor, language, sensory, or behavioral features. Clinicians review pregnancy, birth and neonatal history; past illnesses; growth; seizures; medicines and exposures; three-generation family history where available; and hearing and vision status. Examination may reveal neurological signs, congenital differences, skin findings, or growth patterns that make targeted testing more informative.
Developmental assessment and etiologic investigation should proceed in parallel with needed supports. Families should not have to await molecular confirmation before receiving speech-language, educational, communication, occupational, psychological, or health-related assistance indicated by the individual's functioning (Rodan et al., 2025).
Genetic testing: sequencing, microarray, and targeted assays
Clinical exome sequencing evaluates protein-coding regions of many genes; genome sequencing examines much more of the genome, subject to analytical limitations. Chromosomal microarray identifies certain missing or extra DNA segments, while targeted testing can identify repeat expansions, methylation abnormalities, or specific variants that are inadequately resolved by broad tests. Choice depends on the phenotype, previously completed studies, clinical urgency, laboratory methodology, insurance or health-system access, and shared decision-making.
The American College of Medical Genetics and Genomics strongly recommended in 2021 that exome or genome sequencing be considered as a first- or second-tier test for children with congenital anomalies or developmental delay/intellectual disability. The AAP's 2025 report favors exome/genome sequencing early in most unexplained pediatric GDD/ID evaluations and continues to use chromosomal microarray alongside it where appropriate. These are guidelines for clinical assessment, not a recommendation for unsupervised commercial genome testing (Manickam et al., 2021; Rodan et al., 2025).
What diagnostic yield can and cannot tell us
Diagnostic yield is the proportion of tested people in whom a study identifies a reportable causal or likely causal finding under its defined criteria. It is not the proportion of all intellectual disability caused by genes. Yield varies with cohort selection, severity, additional congenital or neurological features, previous testing, variant interpretation, platform coverage, and access to parental samples. The 2025 AAP report explains that molecular yield can be especially high in some severe or syndromic presentations and lower in many mild presentations; these are population patterns rather than individual predictions (Rodan et al., 2025).
A negative genetic test means that the investigation did not find an explanation using the tested method and available knowledge. It does not establish a purely environmental cause. Exome sequencing may miss some structural changes, repeat expansions, epigenetic abnormalities, mitochondrial mechanisms, and variants in difficult genomic regions. Reanalysis can sometimes identify new information as gene–disease associations become better understood. The appropriate interval and method for further investigation depend on the individual case and current specialist guidance.
Additional examinations are selected by clinical findings
Hearing and vision assessments can reveal reasons for apparent difficulties in communication or testing. Neuroimaging may help when there are focal neurological findings, abnormal head growth, seizures, regression, or suspected structural brain anomalies. Metabolic laboratory testing is especially important if treatable disease is plausible, including a child with regression or episodic illness. Routine indiscriminate testing across every possible mechanism can expose people to incidental findings and unnecessary cost; targeted and broad approaches should be chosen through a coherent clinical plan (Rodan et al., 2025).
What the research establishes—and where uncertainty remains
There is strong clinical evidence that intellectual disability has heterogeneous etiologies; that certain chromosomal and monogenic disorders can be causally associated with impaired cognitive development; that prenatal alcohol exposure can cause FASD; and that defined infections, toxic exposures, and serious neurological injury can affect development. Evidence also supports a meaningful diagnostic role for genomic evaluation in appropriately selected patients. These claims are established in clinical guidelines and official public-health sources (AAIDD, Interrelated Causes of IDD; Manickam et al., 2021; Rodan et al., 2025).
A second evidence category comprises population associations. Prematurity, low birth weight, certain maternal conditions, and neonatal complications correlate with higher rates of developmental difficulties in some studies, but effect sizes vary and confounding can be substantial. The observational meta-analysis by Huang and colleagues is useful for mapping risk categories, yet it does not demonstrate that each recorded characteristic caused intellectual disability in an individual. Its reliance on older studies also limits direct application to current neonatal care and contemporary diagnostic practice (Huang et al., 2016).
A third category includes mechanisms that remain preliminary, incomplete, or contested. Many rare variants have uncertain significance; some cases involve multiple molecular changes or incompletely characterized gene–environment pathways; and causation may remain unresolved even after advanced testing. Broad claims that one everyday exposure, parenting style, screen habit, diet, or social characteristic explains intellectual disability generally are unsupported without disorder-specific evidence. Scientific uncertainty should be located precisely: it concerns the particular etiologic claim, not whether the person deserves assessment and support.
Why estimates differ between studies
Studies enroll different populations and use different thresholds for intellectual disability, developmental delay, or referral to genetic clinics. Some include primarily infants with congenital anomalies; others assess school-aged children with mild difficulties. Testing technologies, genomic variant classifications, gestational-age distributions, health systems, and access to hearing and developmental services also differ. Referral-center results cannot automatically be generalized to all people with intellectual disability. Measures of prevalence, diagnostic yield, causal contribution, and recurrence are distinct and must be reported separately.
Prevention, early recognition, and the limits of prevention
Public-health measures can prevent particular developmental harms: recommended vaccinations can prevent congenital rubella; prenatal alcohol avoidance prevents alcohol-related fetal exposure; lead mitigation reduces a recognized neurotoxic hazard; adequate nutrition and appropriate prenatal care reduce some preventable risks; and newborn screening enables early identification of selected treatable metabolic and endocrine disorders. These actions target known mechanisms and are supported by the corresponding public-health evidence (CDC, Rubella; CDC, FASD; CDC, Lead).
Prevention has defined limits. Many pathogenic variants arise without a recognizable exposure or modifiable precursor, and some genetic conditions are inherited in ways that cannot be inferred from routine pregnancy care. A person can have intellectual disability even when the pregnancy and delivery appeared uncomplicated. Counseling grounded in the actual mechanism is more useful than retrospective blame. Public health, healthcare access, disability inclusion, and personalized supports remain relevant throughout life regardless of whether a cause was preventable.
When a child has persistent global developmental concerns, early developmental and medical evaluation is appropriate. Rapid loss of previously acquired abilities, new seizures, altered consciousness, or other acute neurological changes require urgent medical assessment. These situations call for investigation of potentially active disease rather than a routine wait-and-see approach (Rodan et al., 2025).
What a known cause changes for the person and family
An etiologic explanation may change medical monitoring, screening for additional problems, treatment of specific complications, and family planning. It can improve communication among pediatricians, geneticists, educators, and other professionals. For some families it also supplies language for understanding a previously uncertain developmental course. Yet genetics and medical history are only components of the person's identity and needs. Clinical care should be guided by the individual's goals, consent and supported communication, cultural circumstances, and changing abilities across development.
Intellectual functioning and adaptive behavior are shaped in part by available opportunities and supports. Accessible communication, inclusive instruction, reliable healthcare, assistive technology, and supported choices can improve participation, reduce preventable barriers, and promote well-being even when the underlying cause persists. Determining causation and building a good life are complementary clinical and social tasks, linked through accurate assessment and person-centered planning (AAIDD, Defining Criteria).
Frequently asked questions
Is intellectual disability always inherited?
No. Some causal variants are inherited, some occur de novo, and other cases involve prenatal infections, harmful exposures, acquired neurological injury, or more complex and currently unexplained mechanisms. The likelihood of recurrence in a family depends on an established diagnosis and inheritance pattern. A geneticist or genetic counselor can assess it in the context of personal and family history (Rodan et al., 2025).
Can an uncomplicated pregnancy still result in intellectual disability?
Yes. Genetic and other developmental mechanisms can be present without obvious pregnancy or birth complications. Conversely, a complicated pregnancy does not mean a child will develop intellectual disability. Clinical attribution depends on an evaluation of the developmental profile, medical history, and available evidence.
Can prematurity or lack of oxygen at birth cause intellectual disability?
Serious neurological injury related to oxygen deprivation can contribute to later intellectual and adaptive limitations. Prematurity is associated with increased risk in some populations, particularly with serious complications, but prematurity alone is not a causal diagnosis. A documented sequence of medical findings is needed before attributing an individual outcome to a birth event (Huang et al., 2016; Rodan et al., 2025).
Does identifying a genetic variant always explain the condition?
No. Laboratories classify variants by evidence, and variants of uncertain significance should not be presented as proven causes. Even a confirmed genetic diagnosis may explain only part of a person's presentation. Clinical genetics specialists assess the relationship between the variant, known disease mechanisms, inheritance, and observed features.
Can an individual have intellectual disability without a known cause?
Yes. An unrevealing genetic or medical investigation does not negate well-established intellectual and adaptive limitations. Diagnostic evaluation and individualized supports can proceed while the etiology remains unexplained. Advances in testing may later clarify some cases, but certainty about cause is not a precondition for care.
Does a particular cause determine severity or independence?
No single etiologic label reliably defines an individual's abilities or future participation. Some conditions have characteristic medical or developmental patterns, but within-condition variation can be substantial. Adaptive skills, health, communication, education, environment, and personally chosen supports require direct assessment (AAIDD, Defining Criteria).
Related Articles
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Autism and Intellectual Disability in Adults: Differences and Support — understanding a common co-occurrence without confusing two distinct diagnostic questions.
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Adaptive Functioning in Intellectual Disability: Conceptual, Social, and Practical Skills — Explain diagnostic adaptive skills with everyday functional examples.
References
American Association on Intellectual and Developmental Disabilities. (2022). Interrelated causes of intellectual and developmental disabilities. https://www.aaidd.org/news-policy/policy/position-statements-2/interrelated-causes-of-IDD
American Association on Intellectual and Developmental Disabilities. (n.d.). Defining criteria for intellectual disability. https://aaidd.org/intellectual-disability/definition/
Centers for Disease Control and Prevention. (2024). Congenital CMV and long-term developmental outcomes. https://www.cdc.gov/cytomegalovirus/congenital-infection/index.html
Centers for Disease Control and Prevention. (2025). Rubella symptoms and complications. https://www.cdc.gov/rubella/signs-symptoms/index.html
Centers for Disease Control and Prevention. (2026). About fetal alcohol spectrum disorders. https://www.cdc.gov/fasd/about/
Centers for Disease Control and Prevention. (2026). About alcohol use during pregnancy. https://www.cdc.gov/alcohol-pregnancy/about/index.html
Centers for Disease Control and Prevention. (2026). Why CDC avoids the term elevated for blood lead levels. https://www.cdc.gov/lead-prevention/news/why-we-avoid-the-term-elevated-for-blood-lead-levels.html
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Manickam, K., McClain, M. R., Demmer, L. A., et al. (2021). Exome and genome sequencing for pediatric patients with congenital anomalies or intellectual disability: An evidence-based clinical guideline of the American College of Medical Genetics and Genomics. Genetics in Medicine, 23, 2029–2037. https://doi.org/10.1038/s41436-021-01242-6
Rodan, L. H., Stoler, J., Chen, E., and Geleske, T. (2025). Genetic evaluation of the child with intellectual disability or global developmental delay: Clinical report. Pediatrics, 156(1), e2025072219. https://doi.org/10.1542/peds.2025-072219