Genetic Tests Overview - Gene Clue Spectrum
Genetic testing: Analyzes biomolecules (DNA, RNA, chromosomes, proteins, metabolites) to detect heritable/acquired genetic variations or their effects. Aims: Diagnosis, risk assessment, carrier identification, prenatal/newborn screening, pharmacogenomics.
| Test Type | Indication |
|---|---|
| Diagnostic | Symptomatic; confirm/rule out suspected genetic condition. |
| Predictive | Asymptomatic; assess future disease risk (e.g., Huntington's, BRCA). |
| Carrier | Identify unaffected carriers for family planning (e.g., CF, Tay-Sachs). |
| Prenatal | Fetus at risk for genetic disorders (e.g., Down syndrome, NTDs). |
| Newborn Screening | All newborns for early detection of treatable conditions (e.g., PKU, CH). |
| Pharmacogenomic | Optimize drug selection/dosage based on genetic makeup. |
Testing Techniques - Lab Detective Kit
Genetic testing employs various lab methods to identify chromosomal or gene-level alterations.
| Technique | Principle | Detects | Sample | Key Application/Limitation |
|---|---|---|---|---|
| Karyotyping | Visualizes whole chromosomes (Giemsa) | Aneuploidies, large deletions/duplications | Blood, amniotic fluid, CVS | Down syndrome; Low resolution |
| FISH | Fluorescent probes bind specific DNA | Microdeletions, -duplications, translocations | Blood, tissue, amniocytes | DiGeorge syndrome (22q11); Targeted |
| PCR | DNA amplification | Specific gene mutations, pathogens | Blood, saliva, tissue | CFTR gene test; Target known |
| DNA Microarray | Hybridization to chip oligos | Copy Number Variants (CNVs), SNPs | DNA from various sources | Detects CNVs; Misses balanced translocations |
| NGS | Massively parallel DNA sequencing | Wide range of mutations, novel variants | DNA/RNA from various sources | Exome/genome; Variants of Unknown Significance (VUS) |
⭐ Sanger sequencing remains the gold standard for confirming single nucleotide variants (SNVs) identified by NGS, especially in Mendelian disorders.
Prenatal Diagnosis - Womb's Genetic Peek
- Goal: Detect fetal abnormalities (chromosomal, genetic, structural) before birth.
- Screening Tests: Assess risk; non-invasive.
- Diagnostic Tests: Confirm diagnosis; invasive.
| Feature | Chorionic Villus Sampling (CVS) | Amniocentesis |
|---|---|---|
| Timing | 10-13 weeks | 15-20 weeks |
| Risk (Miscarriage) | ~0.5-1% | ~0.2-0.5% |
| Sample | Chorionic villi (placental) | Amniotic fluid (fetal cells) |
| Tests | Karyotyping, FISH, DNA | Karyotyping, FISH, DNA, AFP |
| NTD Detection | No | Yes (AFP, AChE) |
⭐ Maternal serum alpha-fetoprotein (MSAFP) is ↑ in open neural tube defects (e.g., anencephaly, spina bifida) and ↓ in Down syndrome (Trisomy 21) & Trisomy 18.
- Non-Invasive Prenatal Testing (NIPT): Analyzes cell-free fetal DNA (cffDNA) in maternal blood from 10 weeks; high sensitivity for common aneuploidies (e.g., Trisomies 21, 18, 13).
Genetic Counseling & ELSI - Ethical Gene Guide
- Genetic Counseling Components:
- Pre-test: Assess patient understanding; discuss test purpose, benefits, risks, limitations, alternatives, and potential psychological impact.
- Post-test: Interpret results clearly; discuss implications for patient & family, management options, emotional support, and further testing or referrals.
- Non-directive Approach: Facilitate informed patient choices, respecting autonomy; avoid imposing personal biases or directing decisions.
- ELSI (Ethical, Legal, Social Implications):
- Informed Consent: Voluntary, documented agreement after full disclosure.
- Privacy & Confidentiality: Strict protection of sensitive genetic information.
- Genetic Discrimination: Guard against unfair treatment (e.g., employment, insurance).
- PCPNDT Act: Mandates against sex determination and sex-selective abortions.
⭐ The Pre-Conception and Pre-Natal Diagnostic Techniques (PCPNDT) Act, 1994, is crucial in India to combat female foeticide by regulating the use of prenatal diagnostic tests.
High‑Yield Points - ⚡ Biggest Takeaways
- Pre-test and post-test counseling are mandatory for informed consent and understanding results.
- Karyotyping detects chromosomal aneuploidies; FISH identifies microdeletions/duplications.
- Next-Generation Sequencing (NGS) enables broad genetic screening like exome/genome sequencing.
- Newborn screening is vital for early detection of treatable inherited disorders.
- Prenatal diagnosis (CVS, amniocentesis) is invasive; NIPT offers non-invasive aneuploidy screening.
- Recognize autosomal dominant, recessive, and X-linked inheritance patterns for pedigree analysis.
- Address Ethical, Legal, and Social Implications (ELSI), including genetic discrimination.
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