Genetics · MU Sofia

24. Prenatal and preimplantation genetic testing.

Inside: 17 sections · 16 labelled pictures · 1 table · 31 flashcards · 8 min

Topic 24 of 79 in the MU Sofia syllabus for Genetics (Medicine, Year 3). The free AceMed note covers it in 17 sections, about 1,043 words (8 min of reading), with 31 flashcards.

In this note

  1. Screening for genetic diseases - general principles. Newborn screening. Prenatal screening (BCS and NIPT). Heterozygote carrier screening.
  2. I. GENERAL PRINCIPLES OF GENETIC SCREENING
  3. II. NEWBORN SCREENING
  4. III. PRENATAL SCREENING
  5. A. BIOCHEMICAL SCREENING (BCS)
  6. B. NON-INVASIVE PRENATAL TESTING (NIPT)
  7. IV. HETEROZYGOTE (CARRIER) SCREENING
  8. V. ROLE OF GENETIC COUNSELING
  9. Preimplantation Genetic Tests.
  10. PREIMPLANTATION GENETIC TESTING (PGT)
  11. Embryo Biopsy
  12. Types of Preimplantation Genetic Testing
  13. III. PRENATAL DIAGNOSIS AND PRENATAL GENETIC TESTING
  14. C. GENETIC ANALYSES IN PRENATAL DIAGNOSIS
  15. IV. INDICATIONS FOR PRENATAL GENETIC TESTING
  16. VI. GENETIC COUNSELING IN PRENATAL TESTING
  17. VII. ETHICAL AND PSYCHOSOCIAL ASPECTS

Screening for genetic diseases - general principles. Newborn screening. Prenatal screening (BCS and NIPT). Heterozygote carrier screening.

Genetic screening is the systematic testing of apparently healthy individuals or populations to identify those at increased risk of a genetic disease.

Screening does not confirm a diagnosis. Its role is to select individuals who need further diagnostic testing.

Screening vs Diagnostic Testing

  • Screening → estimates risk, applied to populations
  • Diagnostic testing → confirms disease, applied to individuals at risk

This distinction is fundamental and frequently tested in exams.

I. GENERAL PRINCIPLES OF GENETIC SCREENING

A genetic screening program is justified when:

  • the disease is serious and clinically significant,
  • the disease has a detectable preclinical phase,
  • early detection improves outcome,
  • effective treatment or intervention exists,
  • the screening test is safe, acceptable, accurate, and affordable,
  • confirmatory diagnostic methods are available.

Key Test Characteristics

Sensitivity

  • Ability of the test to correctly identify affected individuals.

Specificity

  • Ability of the test to correctly identify unaffected individuals.

Predictive Values

  • Positive predictive value (PPV): probability that a positive result is true.
  • Negative predictive value (NPV): probability that a negative result is true.

Predictive values depend on disease prevalence.

Ethical and Social Considerations

  • Informed consent
  • Confidentiality
  • Psychological impact
  • Avoidance of stigmatization or discrimination

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