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Diagnostic Testing and Evaluation

Down syndrome may be suspected by prenatal screening or by physical findings at the time of birth. The diagnosis is confirmed by chromosome studies (karyotype).

Diagnostic Criteria

A complete or partial extra copy of chromosome 21 confirms the diagnosis.

First Steps


  • Genetic counseling to review suspected diagnosis and risks/benefits of testing
  • Amniocentesis or umbilical cord blood sampling for karyotype


  • Obtain blood (or other tissue) for karyotype. (2007)

Testing Strategy

Karyotype analysis of cultured blood, amniocytes, chorionic villus or other tissue

  • Highly accurate, provides detailed results
  • Takes 1-2 weeks (2007)

Other techniques are more rapid (24-48 hours), but should be confirmed by standard karyotype.
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  • Fluorescence in situ hybridization (FISH) analysis of uncultured amniocytes or chorionic villus cells
  • Array comparative genome hybridization (CGH) of cultured blood, amniocytes, or chorionic villus cells
    • Can miss more subtle chromosomal rearrangements, including balanced translocations
      (Kirchhoff, Rose et al. 2001; Korbel, Tirosh-Wagner et al. 2009; Fruhman and Van den Veyver 2010; Tan, Palmer et al. 2010)

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 If karyotype normal but clinical presentation still suspicious, evaluate for mosaic Down Syndrome

  • Extended analysis of 30 cells
  • Analysis of different tissue (usually skin fibroblasts)

Tests that are NOT helpful


Subsequent Evaluation

Lifestyle/Environmental Contributors to Disease


Differential Diagnosis

Conditions With Similar Clinical Exams

Similar presentation (Hypotonia, developmental delay, dysmorphic features and congenital malformations) also occur in:

  • Other chromosomal disorders, including complete and partial trisomy or monosomy of other chromosomes and translocations/rearrangements.
    • Karyotype, FISH, CGH and other test methods are of potential value. Genetics consultation is recommended.
  • Peroxisomal disorders

Consensus Statements and Guidelines

None for diagnosis

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