What is the diagnostic process for testing an infant for Down syndrome?

From the Guidelines

The most effective way to test an infant for Down syndrome is through karyotyping, a blood test that examines the baby's chromosomes, as it provides a definitive diagnosis. This test is highly accurate and takes about 1-2 weeks for results 1. Prenatally, screening tests like maternal serum screening and ultrasound examinations can identify risk factors, but they are not definitive. Invasive diagnostic tests such as amniocentesis or chorionic villus sampling (CVS) can be conducted prenatally for a conclusive diagnosis, analyzing fetal cells for the presence of an extra chromosome 21 1.

Key Points for Diagnosis:

• Karyotyping is the gold standard for diagnosing Down syndrome in infants, providing a definitive diagnosis by examining the baby's chromosomes 1.
• Prenatal screening tests, including maternal serum screening and ultrasound, can identify risk factors but are not definitive 1.
• Invasive prenatal diagnostic tests like amniocentesis and CVS can provide a conclusive diagnosis by analyzing fetal cells 1.
• Physical characteristics may suggest Down syndrome, but chromosomal analysis is necessary for a definitive diagnosis 1.

Importance of Early Diagnosis:

Early diagnosis of Down syndrome is crucial as it allows for prompt intervention with appropriate developmental support, monitoring for associated health conditions like heart defects, and connecting families with support resources. The American College of Medical Genetics recommends routine chromosome analysis for any child with unexplained developmental delay or mental retardation, even in the absence of dysmorphic facial features or a positive family history 1.

Testing Process:

For children with clinical features suggestive of Down syndrome, cytogenetic analysis should be performed, and the identification of a translocation may affect the family’s recurrence risk 1. High-resolution chromosome analysis is not routinely indicated unless a specific chromosomal region is to be investigated or there is a family history of a particular abnormality 1. If chromosome analysis is normal at 550-band resolution, subtelomere FISH testing may be considered 1.

From the Research

Diagnostic Process for Down Syndrome

The diagnostic process for testing an infant for Down syndrome involves several steps and methods.

• Physical Examination: A score based on eight signs of Down syndrome can be used to evaluate the likelihood of the condition in a newborn 2. These signs include:
  • Abundant neck skin
  • Mouth corners turned downward
  • General hypotonia
  • Flat face
  • Dysplastic ear
  • Epicanthic eye-fold
  • Gap between first and second toes
  • Protruding tongue
• Chromosome Analysis: Confirmation of the diagnosis is typically done through chromosome analysis, which can be performed prenatally or postnatally 3.
• Prenatal Testing: Prenatal testing techniques, such as sonographic features and fluorescence in situ hybridization (FISH), can detect Down syndrome in the first or second trimester of pregnancy 4, 5.
• Postnatal Care: After a diagnosis of Down syndrome is confirmed, pediatricians can provide guidance on the care and health supervision of the child 3.
• Assessment and Care: Newborns with Down syndrome require specific attention to their presentation, clinical features, physical assessment, and family support 6.

Methods of Detection

Different methods can be used to detect Down syndrome, including:

• Sonographic Features: Sonographic imaging of the second-trimester fetus can identify anatomical features associated with an increased risk of Down syndrome 4.
• Fluorescence in Situ Hybridization (FISH): FISH with chromosome 21-specific DNA probe can be used for rapid prenatal diagnosis of Down syndrome in the first trimester of pregnancy 5.
• Maternal Age and Serum Alpha-Fetoprotein: Combining maternal age and serum alpha-fetoprotein levels can identify approximately 40% of fetuses with Down syndrome 4.