Genetic Testing in Pediatrics

Intro to Pediatric Genetic Testing - Tiny Patients, Big Answers

• Identifies genetic causes for developmental delays, dysmorphic features, metabolic issues, or unexplained syndromes.
• Guides diagnosis, targeted therapy, prognosis, and family recurrence risk counseling.
• Methods range from chromosomal (karyotype, CMA) to molecular (gene panels, WES/WGS).
• Early diagnosis is key for treatable conditions, improving outcomes.
• Integral: Pre-test and post-test genetic counseling.

⭐ Chromosomal Microarray (CMA) is a first-tier test for children with multiple congenital anomalies, unexplained developmental delay, or intellectual disability.

Types of Genetic Tests - The Gene Detective's Kit

• Cytogenetic Tests: Study chromosome structure & number.
  • Karyotyping: Detects aneuploidies (e.g., Trisomy 21), large structural changes. Suspected chromosomal syndromes (e.g., Down, Turner).
  • FISH (Fluorescence In Situ Hybridization): Locates specific DNA sequences. Microdeletions (e.g., 22q11.2), aneuploidy screening.
• Molecular Tests: Examine DNA/RNA at finer resolution.
  • Chromosomal Microarray (CMA): 1st-tier for Developmental Delay/Intellectual Disability (DD/ID), Autism Spectrum Disorders (ASD), Multiple Congenital Anomalies (MCA). Detects Copy Number Variations (CNVs - microdeletions/duplications); higher yield than karyotype for DD/ID.

    ⭐ CMA has a higher diagnostic yield (approx. 15-20%) than karyotyping (approx. 3-5%) for unexplained DD/ID.

  • PCR-based Tests: Amplify specific DNA. Single gene defects (e.g., Fragile X), triplet repeats (e.g., Huntington's).
  • Sanger Sequencing: Specific gene sequence. Confirms single gene mutations.
  • Next-Generation Sequencing (NGS): High-throughput sequencing.
    • Gene Panels: Multiple genes for specific phenotype (e.g., epilepsy, inherited cancers).
    • Whole Exome Sequencing (WES): All protein-coding regions (exome). Complex cases, diagnostic odyssey.
    • Whole Genome Sequencing (WGS): Entire genome. Broader than WES (includes non-coding regions).

Indications for Testing - When to Test Kiddos

• Developmental Delay/Intellectual Disability (DD/ID): Unexplained global delays, ID.
• Multiple Congenital Anomalies (MCA): ≥2 major anomalies or multiple minor ones.
• Dysmorphic Features: Suggestive of a specific genetic syndrome.
• Family History: Known genetic disorder in 1st/2nd degree relatives.
• Parental Consanguinity: Especially for autosomal recessive conditions.
• Neurological Regression: Loss of acquired milestones.
• Ambiguous Genitalia / Disorders of Sex Development (DSD).
• Sensory Deficits: Unexplained hearing or vision loss.
• Growth Disturbances: Significant short stature or overgrowth.
• Positive Newborn Screening: For confirmatory diagnosis.
• Suspected specific syndrome: Based on clinical gestalt.

⭐ Chromosomal Microarray (CMA) is often the first-tier test for children with unexplained Developmental Delay/Intellectual Disability (DD/ID), Autism Spectrum Disorder (ASD), or Multiple Congenital Anomalies (MCA).

Counseling & ELSI - Guidance & Gotchas

• Pre-test Counseling: Crucial for informed consent.

  • Explain test purpose, limitations, implications (medical, psychosocial, financial).
  • Discuss potential results: positive, negative, VUS (Variant of Uncertain Significance).
  • Address autonomy, confidentiality, and potential for genetic discrimination.
  • Explore family implications; cascade testing.

• Post-test Counseling: Interpretation and support.

  • Clearly explain results and their clinical significance.
  • Provide emotional support and resources.
  • Discuss management options, surveillance, and reproductive choices.
  • Address residual risks and follow-up.

• Ethical, Legal, and Social Implications (ELSI):

  • Informed Consent: Mandatory; assent for older children.
  • Confidentiality & Privacy: Protect genetic information.
  • Genetic Discrimination: GINA (USA context, be aware of Indian laws if specified).
  • Testing Minors: Best interest of the child; carrier testing usually deferred.
  • Incidental Findings: Policy for disclosure should be discussed pre-test.

⭐ Non-Directiveness: A core principle in genetic counseling, empowering families to make decisions aligned with their own values, especially for conditions with variable expressivity or adult-onset. Avoid imposing personal views or directing choices. (98 words)

High‑Yield Points - ⚡ Biggest Takeaways

• Karyotyping: For numerical/large structural chromosomal defects (e.g., Trisomy 21, Turner syndrome).
• FISH: Detects known microdeletions/duplications (e.g., 22q11.2 for DiGeorge syndrome).
• CMA: First-tier for unexplained DD/ID, Autism (ASD), & MCA.
• NGS (WES/WGS, panels): For genetically heterogeneous disorders or when clinical diagnosis is unclear.
• Sanger Sequencing: Confirms NGS-found variants or for known single-gene disorders.
• Genetic Counseling: Crucial pre-test and post-test for informed consent.
• Indications: Dysmorphism, family history, DD/ID, MCA, seizures, regression.