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Intellectual Developmental Disorders (Developmental Delay)
Definitions
Intellectual disability (ID) has replaced the older term mental retardation (MR), reflecting a more enlightened and progressive attitude toward individuals with disabilities, both physical and cognitive. ID is characterized by significant limitations in intellectual functioning and in adaptive behavior that begin before age 18 years and are expressed in conceptual, social, and practical adaptive skills. The impairments of ID extend beyond what is measured on a standardized test of intelligence and must take into account the context of an individual’s typical environment and their cultural and linguistic backgrounds. Adaptive functioning includes three broad domains: conceptual, social, and practical. The conceptual domain involves academic competence, the acquisition of practical knowledge, and judgment in novel situations. The social domain involves awareness of others’ thoughts and feelings, empathy, friendships, and social judgment. The practical domain involves the ability to manage one’s own affairs, including school and work responsibilities, money management, and recreation ( Table 27.1 ). Although ID is a lifelong condition, it is recognized that “with appropriate personalized supports over a sustained period, the life functioning of the person with intellectual disability generally will improve.” In a long-term study comparing ID and non-ID siblings, those with mild ID (intelligence quotient [IQ] between 64 and 75) were just as likely to find stable employment, to have similar total family incomes, to have stable marriages, and to raise children as their siblings. However, they reported higher rates of psychologic distress and lower rates of participation in formal organizations. Table 27.2 provides descriptions of typical adult functioning in individuals with varying degrees of ID.
TABLE 27.1
Diagnosis of Intellectual Disability
Data from American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders (DSM-V) . 5th ed. Arlington, VA: American Psychiatric Association; 2013.
| Diagnostic Criteria |
| All Three Criteria Must Be Met |
|
| Assumptions |
|
TABLE 27.2
Severity of Intellectual Disability and Adult Age Functioning
From Schum RL. Grand Rounds Presentation at Children’s Hospital of Wisconsin; 2003.
| Level | Mental Age as an Adult ∗ | Adult Adaptation |
|---|---|---|
| Mild | 9–11 yr | Reads at fourth- to fifth-grade level; simple multiplication/division; writes simple letters, lists; completes job applications; basic independent job skills (arrive on time, stay at task, interact with coworkers); uses public transportation, may qualify for driver’s license; keeps house, cooks using recipes |
| Moderate | 6–8 yr | Sight-word reading; copies information, e.g., address from card to job application; matches written number to number of items; recognizes time on clock; communicates; some independence in self-care; housekeeping with supervision or cue cards; meal preparation, can follow picture recipe cards; job skills learned with much repetition; uses public transportation with some supervision |
| Severe | 3–5 yr | Needs continuous support and supervision; may communicate wants and needs, sometimes with augmentative communication techniques |
| Profound | <3 yr | Limitations of self-care, continence, communication, and mobility; may need complete custodial or nursing care |
∗ International Statistical Classification of Diseases and Related Health Problems. 10th revision. World Health Organization; 2010.
The term developmental disability includes a diverse group of lifelong physical and mental impairments that negatively affect an individual’s ability to function as well as their peers. These conditions begin during childhood (before 22 years of age) and interfere with mobility, acquisition of self-care ability, communication skills, social skills, general learning ability, and independent living. The specific types of conditions and categories of disabilities vary widely. The National Institute for Child Health and Development (NICHD) includes the following conditions: neurologic disorders: cerebral palsy, muscular dystrophy, epilepsy, genetic syndromes, autism, and degenerative disorders; sensory disorders: blindness and deafness; metabolic disorders: phenylketonuria (PKU); and cognitive disorders: intellectual impairment, learning disabilities, and attention-deficit/hyperactivity disorder (ADHD). Developmental disabilities may be isolated, as in a child with impaired vision, or may be multiple, as in a child with delays in motor, cognitive, language, and social functioning. There may be considerable overlap in specific disorders in terms of the affected functions ( Fig. 27.1 ). In young children, developmental delays may result from a wide range of causes, including early environmental understimulation, chronic physical illness, neuromuscular disorders, central nervous system (CNS) abnormalities, and genetic syndromes ( Tables 27.3 and 27.4 ). Some etiologies are fully or partly amenable to early educational and medical interventions, while others may lead to permanent intellectual impairment or progressive deterioration of functioning. Therefore, until a young child has had the benefit of early intervention services and has matured to the point where formal cognitive, language, and adaptive measures are stable and predictive of future functioning, the descriptive term global developmental delay (GDD) is preferred.
TABLE 27.3
Prevalence of Select Conditions Associated with Developmental Delay
| Condition | Prevalence/100,000 | Comments |
|---|---|---|
| Cerebral palsy | 250–270 | Represents many causes |
| Significant hearing loss | 150 | In neonatal period |
| Down syndrome | 98–125 | Prevalence at birth |
| Fragile X syndrome | 117 | Predominantly in boys |
| Meningomyelocele | 60–100 | Prevalence at birth |
| Klinefelter syndrome | 100 | 15% have intelligence quotient (IQ) <80 |
| Fetal alcohol syndrome | 60–800 | Present at birth |
| Congenital HIV infection | 5–50 | Preventable with maternal and neonatal therapy |
| Blindness | 41–88 | Syndromic, genetic, prematurity risks |
| Infantile hydrocephalus | 64 | Prevalence at birth |
| Neurofibromatosis | 33 | 5% have intellectual disability |
| Trisomy 18 | 30 | Prevalence at birth |
| Trisomy 13 | 20 | Prevalence at birth |
| Turner syndrome | 20 | IQ may be normal |
| Prader-Willi syndrome | 13–20 | In childhood |
| Galactosemia | 14 | In infancy |
| Phenylketonuria | 6–12 | In infancy |
| Anophthalmia | 6 | Consider other anomalies |
| Rett syndrome | 4–5 | In females 2–18 yr of age |
| Histidinemia | 3 | At birth |
| Acrocephalosyndactylia (Apert syndrome) | 1–2 | Present at birth |
TABLE 27.4
Identification of Cause in Children with Significant Intellectual Disability
From Kliegman RM, St. Geme J. Nelson Textbook of Pediatrics . 21st ed. Vol 1. Philadelphia: Elsevier; 2020:284, Table 53.1 .
| Cause | Examples | % of Total |
|---|---|---|
| Chromosomal disorder | Trisomies 21, 18, 13 Deletions 1p36, 4p, 5p, 11p, 12q, 17p Microdeletions Klinefelter, 47,XXX, and Turner syndromes |
∼20 |
| Genetic syndrome | Fragile X, Prader-Willi, Angelman, and Rett syndromes | ∼20 |
| Nonsyndromic autosomal mutations | Variations in copy number; de novo mutations in SYNGAP1 , GRIK2 , TUSC3 , oligosaccharyl transferase, and others | ∼10 |
| Developmental brain abnormality | Hydrocephalus ± meningomyelocele; schizencephaly, lissencephaly | ∼8 |
| Inborn errors of metabolism or neurodegenerative disorder | Phenylketonuria, Tay-Sachs disease, various storage diseases | ∼7 |
| Congenital infections | HIV, toxoplasmosis, rubella, cytomegalovirus, syphilis, herpes simplex, Zika virus | ∼3 |
| Familial intellectual disability | Environment, syndromic, or genetic | ∼5 |
| Perinatal causes | Hypoxic-ischemic encephalopathy, meningitis, intraventricular hemorrhage, periventricular leukomalacia, fetal alcohol syndrome | 4 |
| Postnatal causes | Trauma (abuse), meningitis, hypothyroidism | ∼4 |
| Unknown | 20 |
Epidemiology
Intellectual Disability
The overall prevalence of ID varies from 1% to 3%, depending on the criteria used and the age of the individual at the time of evaluation. Standardized tests of intelligence have a mean of 100 and standard deviation of 15 points. Statistically, 2.5% of individuals should have an IQ score below 2 standard deviations (70 points) and fit the cognitive criterion for ID. However, because the standard error of measurement is approximately 5 points, extending the IQ score upward to 75 points would almost double the prevalence of ID. This might be countered by secondary criteria involving deficits in adaptive behaviors, since many children with IQ scores in the mildly low range (55–70) will not qualify for a diagnosis of ID because they have adequate adaptive functioning. Many studies have documented a higher rate of mild ID in economically disadvantaged children that stems from a few highly significant sociodemographic risk factors.
Developmental Disability
Developmental disabilities affect approximately one in six children in the United States (16.9%). The prevalence rates vary by specific condition: ADHD (9.54%), learning disability (7.86%), autism (2.49%), and ID (1.17%) are the most common, while epilepsy, deafness, cerebral palsy, and blindness each affect <1%. Males have more than twice the prevalence of any developmental disability, and children insured by Medicaid have a prevalence of disability that is approximately 1½ times greater than those with private insurance. The overall prevalence of disability increased by 9.5% between 2009–2011 and 2015–2017, mostly due to a 122.3% increase in autism (from 1.12% to 2.49%). In addition, the prevalence of ID increased 25.8% (from 0.93% to 1.17%).
Table 27.3 lists the prevalences of selected conditions.
Diagnosis
Identification of a specific cause for delayed development in a child is important and may provide insight into prognosis, recurrence risk, therapies, counseling, and linkage with a supportive group. Identification of the child’s functional abilities, strengths and weaknesses, overall physical health, and environmental factors is critical for optimizing the child’s health, development, and functioning. In addition, the origin of developmental disability is not apparent in many children, or there may be multiple possible causal factors or multiple disabilities present. For example, 23% of children with developmental disabilities have two disabilities, and 6% have three or more. Even if a specific diagnosis cannot be made, early identification of developmental delay can lead to a program of early intervention or remediation that may improve the child’s ultimate functioning. To identify those disorders that are amenable to intervention, an international consortium has developed both a web-based tool and a mobile application (app) to assist practitioners in the evaluation and management of children with ID ( http://www.treatable-id.org/ ).
Identification
Children who experience significant complications in the perinatal period or who are born with obvious congenital anomalies are at risk for developmental disabilities. In addition, newborn screening programs may identify children with rare but significant problems who require early treatments and interventions. Children with no apparent risk factors or obvious physical or neurologic symptoms may be identified through a process of surveillance and screening during routine child health care visits.
Developmental Risk Factors
Young children’s development may be adversely affected by biologic and/or sociocultural risk factors ( Table 27.5 ). Many risk factors can be graded according to severity (e.g., degree of prematurity, intracranial hemorrhage, intrauterine growth restriction), but it is often the cumulative effect of multiple factors that ultimately determines a child’s developmental outcome, even when one or more “severe” risks are present. It has been shown that low 5-minute Apgar scores, in the absence of other symptoms of neonatal encephalopathy, may correlate poorly with long-term neurologic dysfunction. Sociocultural risks also can have profound effects on development and may interact with biologic risk factors to create a greater effect than any single factor alone (so-called “double jeopardy”).
TABLE 27.5
Risk Factors for Developmental Disabilities
| Biologic | Sociocultural |
|---|---|
|
|
Developmental Protective Factors
During the process of developmental surveillance, the clinician should identify and acknowledge the influence of protective and supportive factors that may contribute to positive outcomes. Barring catastrophic circumstances, child-rearing conditions that support and enrich early development may compensate for biologic deficits. Sociocultural factors, such as small family size, higher level of parental education, and fewer changes in residence, have a more powerful positive effect than many biologic risks and seem to be important predictors of developmental functioning beyond infancy. The brains of infants and young children are remarkably resilient and normal cognitive and language outcomes are often seen, even in the face of perinatal stroke or similar focal brain injuries. Neural plasticity also extends to situations of extreme environmental deprivation, providing interventions occur early enough. In addition, preschool early intervention programs that are designed to mitigate the factors that place children at risk for poor outcomes have been shown to have significant short- and long-term educational, behavioral, and economic benefits.
Screening for Specific Abnormalities
Deficits in vision, hearing, and language can have devastating effects on development; early intervention to ameliorate these problems can improve outcomes. All children should be screened on a regular basis for these conditions.
Visual Deficits
Children at high risk for development of deficits in vision (see Chapter 43 ) include those with strabismus (especially after 4 months of age), hydrocephalus, congenital infection, neonatal encephalopathy, congenital anomaly of the CNS, prematurity with exposure to oxygen, and family history of a childhood onset of visual impairment. All neonates should routinely undergo an evaluation of their fundi for the presence of a red reflex, which can be obscured by cataract or tumor, as well as inspection of the globe, which may be enlarged by congenital glaucoma. Infants with nystagmus who do not follow (tract) visually by 3 months of age, who have dissociation between visual behavior and motor behavior, or whose parents express concern about their vision should undergo a formal ophthalmologic evaluation.
Preschool children should undergo periodic evaluations of extraocular movements to rule out strabismus and amblyopia; the evaluation should include visual inspection of the child’s eyes, the Hirschberg light test, and the cover-uncover test. As early in the child’s development as possible, specific tests of monocular and binocular vision such as Allen cards (3–5 years), the Snellen chart (>5 years), or the Titmus test (>4 years) should be performed.
Loss of Hearing
Early detection of hearing loss is critical for optimizing the language development of these children. Universal newborn hearing screening programs (UNHSPs) can detect infants born with moderate, severe, or profound bilateral hearing impairment. Although the prevalence of congenital deafness is low in the general population (1–3/1,000 infants), it is higher in infants who require neonatal intensive care services (2–4/100 infants). More than half of babies with permanent congenital hearing impairment do not have prospectively identifiable risk factors and would be missed without UNHSPs. They would not receive hearing intervention within the first 6 months of life, a period that is critical for speech, language, and later learning development. Hearing loss can be acquired during infancy or childhood from infection (cytomegalovirus [CMV], meningitis), trauma (particularly basal skull and temporal bone fractures), ototoxic drugs (aminoglycosides, furosemide), or damaging noise levels. A number of genetic syndromes are associated with deafness (Waardenburg, Alport, Pendred, and Jervell and Lange-Nielsen), and progressive or late-onset hearing loss can occur in neurofibromatosis, Usher syndromes, Hunter syndrome, Friedreich ataxia, or Charcot-Marie-Tooth syndrome ( Table 27.6 ). Children with one or more “risk factors” should have hearing screening again at 24–30 months, even if they passed the newborn screening test. In addition, parental concern about hearing loss has a sensitivity of approximately 44%. If parents express concern about their child’s ability to hear and if the child has had recurrent episodes of otitis media, mastoiditis, or one of the perinatal or familial risk factors, a formal audiometric screening should be performed. Table 27.7 lists the latest acceptable age (“limit ages”) for the appearance of skills related to hearing; absence of these milestones may indicate a disorder of hearing. Deaf infants may smile, coo, and babble; however, their vocalizations usually cease after 8 months of age.
TABLE 27.6
Risk Indicators Associated with Permanent Congenital, Delayed-Onset, and/or Progressive Hearing Loss in Children
From American Academy of Pediatrics, Joint Committee on Infant Hearing. Pediatrics . 2007;120(4):898–921.
|
CMV, cytomegalovirus; ECMO, extracorporeal membrane oxygenation.
∗ Risk indicators that are of greater concern for delayed-onset hearing loss.
TABLE 27.7
Latest Acceptable Age for Skills Related to Hearing ∗
Modified from the Arizona Speech, Language, Hearing Association.
| Age (mo) † | Activity |
|---|---|
| 3 | Not startling to loud sounds |
| 6 | Not smiling to voice; not vocalizing |
| 9 | Does not localize speech or other sounds |
| 12 | Not babbling multiple sounds and syllables |
| 18 | No words |
| 24 | <50% of speech understandable |
∗ A child who does not demonstrate the activity by the stated age should have formal audiometry performed.
Speech and Language Disorders
Disorders of speech and language development, prevalent in 3–20% of preschool children, are the most common reason for referral to early intervention programs and are correlated with subsequent learning problems. Speech refers to the mechanics of oral communication (sound production); language includes the understanding, processing, and production of communication (words). Speech problems may include articulation (pronunciation) deficits (phonologic or apraxic speech disorders), fluency disorders (stuttering), or unusual voice quality. Language delays may be confined to expression with normal receptive abilities or may involve both expressive and receptive abilities. Language delays may be a feature of GDD/ID, autism spectrum disorders (ASDs), or hearing impairment, or may be the result of an isolated disorder (specific language impairment).
Children with speech and language delays often experience emotional and social adjustment difficulties related to their inability to communicate effectively with parents and peers. In general, children with normal comprehension of language and normal nonverbal cognitive abilities have an excellent prognosis, while those with receptive delays are at risk for language-based learning disabilities (reading comprehension and writing disorders) ( Table 27.8 ).
TABLE 27.8
Speech-Language Screening for Pediatricians
From Schum RL. Language screening in the pediatric office setting. Pediatr Clin North Am . 2007;54:425–436.
| Refer for a Speech-Language Evaluation If: | ||
|---|---|---|
| At Age | Receptive | Expressive |
| 15 mo | Does not look/point at 5–10 objects/people named by a parent | Not using three words |
| 18 mo | Does not follow simple directions (“Get your shoes”) | Not using Mama, Dada, or other names |
| 24 mo | Does not point to pictures or body parts when they are named | Not using 25 words |
| 30 mo | Does not verbally respond or nod/shake head to questions | Not using unique two-word phrases, including noun-verb combinations |
| 36 mo | Does not understand prepositions or action words; does not follow two-step directions | Vocabulary <200 words; does not ask for things by name; echolalia to questions; regression of language after acquiring two-word phrases |
Prenatal and Newborn Screening Programs
Prenatal Screening
Prenatal screening has undergone significant changes with the advent of next-generation sequencing (NGS) technologies. The traditional screening takes the form of biochemical and ultrasound tests, which may detect fetuses at high risk for chromosome anomalies and neural tube defects. In the first trimester (11–14 weeks’ gestation), measurement of maternal serum levels of human chorionic gonadotropin (hCG) and pregnancy-associated plasma protein A (PAPP-A) and a sonogram measurement of the fluid underneath the skin along the back of the fetus’s neck (nuchal translucency) may identify Down syndrome, trisomy 13, or trisomy 18. In the second trimester (15–22 weeks’ gestation), a quad screen (α-fetoprotein, hCG, estriol, and inhibin A levels) may identify Down syndrome and neural tube defects (spina bifida, encephalocele). An abnormal result on these screenings is typically followed by high-resolution ultrasonography, chorionic villus sampling or amniocentesis, genetic testing (chromosome analysis or microarray), and genetic counseling. NGS technologies allow for noninvasive prenatal screening (NIPS) on maternal blood samples, also called cell-free fetal DNA prenatal screening. These technologies identify possible chromosomal and microdeletion disorders through maternal blood screening. If an abnormality is detected, a confirmatory test is still required through more invasive techniques such as amniocentesis. In addition, prenatal genetic carrier screening can be performed for a large number of disorders; at present, these are the only standard of care for individuals at high risk for certain genetic conditions (e.g., Tay-Sachs).
Newborn Screening
Uniform newborn screening is highly successful in identifying children with rare but serious conditions who can benefit from early intervention. All 50 states, U.S. territories, and the U.S. military routinely test for inborn errors of metabolism (IEMs), congenital hypothyroidism, congenital adrenal hyperplasia, severe T-cell immunodeficiency (SCID), cystic fibrosis, and hemoglobinopathies. Test samples should be collected between 24 and 48 hours of age, but results may be influenced by a variety of maternal and infant factors. Tests for congenital adrenal hyperplasia are sensitive to the weight of the infant and the use of steroids. Screening for hypothyroidism (thyroid-stimulating hormone [TSH]) may be falsely low in premature or low birthweight infants. The use of antibiotics and total parenteral nutrition (TPN) may interfere with interpretation of newborn metabolic screening tests. While all states screen for a “core panel” of 29 conditions, they vary in testing for other conditions. An additional 26 conditions have been recommended for inclusion in the U.S. Health and Human Services Recommended Uniform Screening Panel. Normal newborn screening test results do not eliminate the possibility that a clinically symptomatic child could have one of the disorders in the state’s panel.
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