Global developmental delay
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Routine screening for inborn errors of metabolism in children with global developmental delay has a low yield of about 1% but may increase to 5% in certain situations or 14% with stepwise screening. Cytogenetic studies have a yield of 3.7% for identifying abnormalities. Fragile X testing has a yield of 2.6% overall but is higher in males. Rett syndrome should be considered in females with unexplained moderate to severe delays, though evidence for testing in milder or male cases is limited. Subtelomeric rearrangement testing has a 6.6% yield in children with unexplained moderate to severe delays. Lead and thyroid screening may be considered for targeted populations.
Global developmental delay
- 1. Practice parameter: Evaluation of the child with global developmental delay
- 2. AAN evidence classification scheme for a diagnostic article Class I: Evidence provided by a prospective study in a broad spectrum of persons with the suspected condition, using a “gold standard” for case definition, where the test is applied in a blinded evaluation, and enabling the assessment of appropriate tests of diagnostic accuracy. Class II: Evidence provided by a prospective study of a narrow spectrum of persons with the suspected condition, or a well designed retrospective study of a broad spectrum of persons with an established condition (by “gold standard”) compared to a broad spectrum of controls, where test is applied in a blinded evaluation, and enabling the assessment of appropriated tests of diagnostic accuracy.
- 3. AAN evidence classification scheme for a diagnostic article Class III: Evidence provided by a retrospective study where either persons with the established condition or controls are of a narrow spectrum, and where test is applied in a blinded evaluation. Class IV: Any design where test is not applied in blinded evaluation OR evidence provided by expert opinion alone or in descriptive case series (without controls).
- 4. AAN system for translation of evidence to recommendations Translation of evidence to recommendations Rating of recommendations Level A rating requires at least one convincing class I study or at least two consistent, convincing class II studies A = Established as useful/predictive or not useful/predictive for the given condition in the specified population Level B rating requires at least one convincing class II study or overwhelming class III evidence B = Probably useful/predictive or not useful/predictive for the given condition in the specified population
- 5. AAN system for translation of evidence to recommendations Translation of evidence to recommendations Rating of recommendations Level C rating requires at least two convincing class III studies C = Possibly useful/predictive or not useful/predictive for the given condition in the specified population U = Data inadequate or conflicting. Given current knowledge, test, predictor is unproven
- 6. Introduction • Developmental disabilities are a group of related chronic disorders of early onset estimated to affect 5% to 10% of children. • Global developmental delay is a subset of developmental disabilities defined as significant delay in two or more of the following developmental domains: – gross/fine motor – speech/language, cognition – social/personal – activities of daily living • Significant delay is defined as performance two standard deviations or more below the mean on age-appropriate, standardized norm-referenced testing.
- 7. Introduction The term global developmental delay is usually reserved for younger children (i.e., typically less than 5 years of age), whereas the term mental retardation is usually applied to older children when IQ testing is more valid and reliable. Prevalence: • The precise prevalence of global developmental delay is unknown. • Estimates of 1% to 3% of children younger than 5 years of age are reasonable given the prevalence of mental retardation in the general population. • Based on approximately 4 million annual births in the United States and Canada, between 40,000 to 120,000 children born each year in these two countries will manifest global developmental delay.
- 10. Analysis of the Evidence Cytogenetic studies testing for Rett syndrome • Patients with classic Rett syndrome appear to develop normally until 6 to 18 months of age, then gradually lose speech and purposeful hand use, and develop abnormal deceleration of head growth that may lead to microcephaly. • Seizures, autistic-like behavior, ataxia, intermittent hyperventilation, and stereotypic hand movements occur in most patients. • Rett syndrome is believed to be one of the leading causes of global developmental delay/mental retardation in females and is caused by mutations in the X-linked gene encoding methyl- CpG-binding protein 2 (MECP2). About 80% of patients with Rett syndrome have MECP2 mutations.
- 11. Analysis of the Evidence Cytogenetic studies testing for Rett syndrome • The prevalence of Rett syndrome in the general population is approximately 1 to 3 individuals per 10,000 live births and it has been estimated that there are approximately 10,000 individuals in the United States with this disorder. • Currently there are insufficient data to estimate the prevalence of Rett syndrome variants in milder affected females or in males.
- 12. Cytogenetic studies Molecular screening for subtelomeric chromosomal rearrangements • The accumulated data suggest that cytogenetic studies will be abnormal in 3.7% of children with global developmental delay, a yield that is likely to increase in the future as new techniques are employed. • In mixed populations (both males and females), a yield of between 0.3% and 5.3% (average yield of 2.6%) has been demonstrated for fragile X testing. The higher range of this yield exists for testing amongst males. • There is a suggestion that clinical preselection for the fragile X syndrome amongst males may improve diagnostic testing beyond routine screening.
- 13. Conclusions • After Down syndrome, Rett syndrome is believed to be the most common cause of developmental delay in females. • Although milder variants in females and more severe phenotypes in males recently have been recognized, estimates of their prevalence are not currently available. • Subtelomeric chromosomal rearrangements have been found in 6.6% (0-11.1%) of patients with idiopathic moderate to severe developmental delay.
- 14. Recommendations 1. Given the low yield of about 1%, routine metabolic screening for inborn errors of metabolism is not indicated in the initial evaluation of a child with global developmental delay provided that universal newborn screening was performed and the results are available for review. Metabolic testing may be pursued in the context of historical (parental consanguinity, family history, developmental regression, episodic decompensation) or physical examination findings that are suggestive of a specific etiology (or in the context of relatively homogeneous population groups) in which the yield approaches 5% (Level B; class II and III evidence). If newborn screening was not performed, if it is uncertain whether a patient had testing, or if the results are unavailable, metabolic screening should be obtained in a child with global developmental delay.
- 15. Recommendations 2. Routine cytogenetic testing (yield of 3.7%) is indicated in the evaluation of the child with developmental delay even in the absence of dysmorphic features or clinical features suggestive of a specific syndrome (Level B; class II and III evidence). 3. Testing for the fragile X mutation (yield of 2.6%) particularly in the presence of a family history of developmental delay, may be considered in the evaluation of the child with global developmental delay. Clinical preselection may narrow the focus of who should be tested without sacrificing diagnostic yield. Although screening for fragile X is more commonly done in males because of the higher incidence and greater severity, females are frequently affected and may also be considered for testing. Because siblings of fragile X patients are at greater risk to be symptomatic or asymptomatic carriers, they can also be screened (Level B; class II and class III evidence).
- 16. Recommendations 4. The diagnosis of Rett syndrome should be considered in females with unexplained moderate to severe mental retardation. If clinically indicated, testing for the MECP2 gene deletion may be obtained. Insufficient evidence exists to recommend testing of females with milder clinical phenotypes or males with moderate or severe developmental delay (Level B; class II and class III evidence). 5. In children with unexplained moderate or severe developmental delay, additional testing using newer molecular techniques (e.g. FISH, microsatellite markers) to assess for subtelomeric chromosomal rearrangements (6.6%) may be considered (Level B; class II and class III evidence).
- 17. Clinical Question What is the role of lead and thyroid screening in children with global developmental delay?
- 18. Analysis of the Evidence Lead Screening • Lead is the most common environmental neurotoxin. Studies over several decades have shown a relation between marked elevations in serum lead levels, clinical symptoms and cognitive deficits (but not definitively mental retardation). • Average blood lead levels in the United States have fallen dramatically from 15µg/dL in the 1970s to 2.7µg/dL in 1991 through 1994. • It is estimated that there are still about 900,000 children in the United States between the ages of 1 and 5 years who have blood lead levels equal to or greater than 10 µg/dL.
- 19. Analysis of the Evidence Lead Screening The recently published guidelines of the American Academy of Pediatrics, candidates for targeted screening include children 1 to 2 years of age living in housing built before 1950 situated in an area not designated for universal screening, children of ethnic or racial minority groups who may be exposed to lead-containing folk remedies, children who have emigrated (or been adopted) from countries where lead poisoning is prevalent, children with iron deficiency, children exposed to contaminated dust or soil, children with developmental delay whose oral behaviors place them at significant risk for lead exposure, victims of abuse or neglect, children whose parents are exposed to lead (vocationally, avocationally, or during home renovation), and children of low-income families.
- 20. Analysis of the Evidence Thyroid Screening • Unrecognized congenital hypothyroidism is a potentially treatable cause of later developmental delay. Delay in diagnosis and treatment beyond the newborn period and early infancy has been clearly linked to later often substantial, neurodevelopmental sequelae. • Implementation of newborn screening programs has been extremely successful in eliminating such sequelae. • In some countries, where comprehensive newborn screening programs are not yet in place, congenital hypothyroidism has been found to be responsible for 17/560 (3.8%) cases of cognitive delay evaluated in a pediatric neurology clinic (class II Study). Many of these children also had prominent systemic symptoms.
- 21. Conclusions • Low-level lead poisoning is associated with mild cognitive impairments but not with global developmental delay. • Approximately 10% of children with developmental delay and identifiable risk factors for excessive environmental lead exposure may have an elevated lead level. • In the absence of systematic newborn screening, congenital hypothyroidism may be responsible for approximately 4% of cases of cognitive delay.
- 22. Recommendations 1. Screening of children with developmental delay for lead toxicity may be targeted to those with known identifiable risk factors for excessive environmental lead exposure as per established current guidelines (Level B; class II evidence). 2. In the setting of existing newborn screening programs for congenital hypothyroidism, screening of children with developmental delay with thyroid function studies is not indicated unless there are systemic features suggestive of thyroid dysfunction (Level B; class II evidence).
- 23. Clinical Question What is the diagnostic yield of EEG in children with global developmental delay?
- 24. Analysis of the Evidence EEG • Although the yield on routine testing is negligible, if there is a suspected epileptic syndrome that is already apparent from the history and physical examination (e.g., Lennox- Gastaut syndrome, myoclonic epilepsy, Rett syndrome), the EEG has confirmatory value.
- 25. Conclusions • Available data from two class III and one class IV study determined an epilepsy- related diagnosis in 11 of 250 children (4.4%). However, the actual yield for a specific etiologic diagnosis occurred in only 1 patient (0.4%).
- 26. Recommendations 1. An EEG can be obtained when a child with global developmental delay has a history or examination features suggesting the presence of epilepsy or a specific epileptic syndrome (Level C; class III and IV evidence). 2. Data are insufficient to permit making a recommendation regarding the role of EEG in a child with global developmental delay in whom there is no clinical evidence of epilepsy (Level U; class III and IV evidence).
- 27. Clinical Question What is the diagnostic yield of neuroimaging in children with global developmental delay?
- 28. Conclusions • Available data primarily from class III studies show that CT contributes to the etiologic diagnosis of global developmental delay in approximately 30% of children, with the yield increasing if physical examination findings are present. • MRI is more sensitive than CT, with abnormalities found in 48.6% to 65.5% of children with global delay with the chance of detecting an abnormality increasing if physical abnormalities, particularly cerebral palsy, are present.
- 29. Recommendations 1. As the presence of physical findings (e.g., microcephaly, focal motor findings) increases the yield of making a specific neuroimaging diagnosis, physicians can more readily consider obtaining a scan in this population (Level C; class III evidence). 2. If available, MRI should be obtained in preference to CT scanning when a clinical decision has been made that neuroimaging is indicated (Level C; class III evidence). Neuroimaging is recommended as part of the diagnostic evaluation of the child with global developmental delay (Level B; class III evidence).
- 30. Clinical Question Are vision and hearing disorders common in children with global developmental delay?
- 31. Conclusions • Several class III studies have shown that children with global developmental delay are at risk to have primary sensory impairments of vision and hearing. Estimates of vision impairment or other visual disorders range from 13% up to 50% whereas significant audiologic impairments occur in about 18% of children based on data in one series of patients.
- 32. Recommendations 1. Children with global developmental delay may undergo appropriate vision and audiometric assessment at the time of their diagnosis (Level C; class III evidence). 2. Vision assessment can include vision screening and a full ophthalmologic examination (visual acuity, extra-oculo- movements, fundoscopic) (Level C; class III evidence). 3. Audiometric assessment can include behavioral audiometry or brainstem auditory evoked response testing when feasible (Level C; class III evidence). Early evidence from screening studies suggest that transient evoked otoacoustic emissions should offer an alternative when audiometry is not feasible (Level A; class I & II evidence).
- 33. To view the entire guideline and additional AAN guidelines visit: AAN.com/Guidelines