Definitions:

1. Significant Developmental Delay?3 2 SD’s below the mean performance in any one category on Denver Developmental Scale
2. Global Developmental Delay?significant delay (by at least 2 SD’s) in 3 2 developmental categories (gross/fine Motor, Speech, Cognition, Social/Personal, activities of daily living)
3. The term "GDD" is usually reserved for children less than 5 yo; the term Mental Retardation is applied to older children, when MR severity is quantifiable with IQ testing

Developmental disabilities are relatively common in children, with 5-10% prevalence. GDD is estimated to be prevalent in 1-3% children < 5 yo. There are many possible causes for the clinical picture of GDD and some causes are treatable. Therefore, early recognition and diagnosis is important. In addition, some of the etiologies are genetically transmitted and may affect future family members..

Differential Diagnosis

1. Chromosomal

1. Down syndrome(trisomy 21)
2. Fragile X syndrome(FMR1 gene, CGG triplet repeat expansion): arguably the most common cause of male GDD/MR, but female sibs may also be affected; typical phenotype includes MR, prominent ears, shyness, poor eye contact
3. Rett syndrome( MECP2 gene mutation): arguably the most common cause of female GDD/MR; typical history includes normal development up to 6-18 mo, then gradual loss of speech and purposeful hand use, deceleration of head growth/microcephaly, seizures, ataxia, autistic behavior, stereotypic hand movements.

1. Metabolic

1. Hypothyroidism?usually picked up on neonatal screen
2. Glycogen storage diseases

4. Environmental deprivation

5. Language and Autistic spectrum disorders
6. Vision and hearing sensory impairments

Stepwise Diagnostic approach: (see summary flowchart below)

1. History is very important! Find out: pattern of development, any loss of milestones/decompensation, family history of MR, history of miscarriages in mother, consanguinity in family
2. Physical exam?look for dismorphic features, organomegaly, abnormal tone, autistic features in behavior

1. Do NOT order metabolic screen routinely, obtain records of neonatal metabolic screen instead (amino and organic acids, thyroid function tests), especially if history is positive for loss of milestones, consanguinity in family
2. Do NOT order Lead level routinely, instead screen children with risk factors for lead exposure (low SES, housing built before 1950, developmentally delayed with oral affinity, children whose parents are exposed)
3. Do NOT order EEG routinely but only if suspect epilepsy

 

 
 
 
 
 
 
 
 
 

4. Cytogenetic testing and karyotype to check for Down, Rett, Fragile X syndromes
5. FISH/microsatellite array tests to detect subtelomeric chromosomal rearrangements.
6. Imaging?MRI is better than CT in detecting cerebral malformations
7. Auditory and Ophthalmologic screening?should be ROUTINE for GDD children as they are more likely to have deficits than healthy kids, and these sensory deficits are likely to confound the picture of GDD
8. Autism/language disorder screening

References:

Shevell, M. et al. Practice Parameter: Evaluation of the child with global developmental delay. Neurology 60, February 1(2003): 367-80.
Roberts,G et al. A rational approach to the medical evaluation of a child with developmental delay. Contemporary Pediatrics March 2004
Committee on Genetics.  Clinical Genetic Evaluation of the Child with Mental Retardation or Developmenbtal Delays.  Pediatrics June 2006
Srour,M et al.  Analysis of Clinical Features Predicting Etiologic Yield in the Assessment of Global Developmental Delay. Pediatrics july 2006