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Genetics and Prenatal Screening

Genetics and Prenatal Screening. Genetics. Each human cell contains 46 chromosomes made up of DNA. Short segments of DNA are called “genes” Dominant and Recessive Genes When one is “dominant” then that expression “trumps” the recessive gene. Carriers?

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Genetics and Prenatal Screening

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  1. Genetics and Prenatal Screening

  2. Genetics • Each human cell contains 46 chromosomes made up of DNA. • Short segments of DNA are called “genes” • Dominant and Recessive Genes • When one is “dominant” then that expression “trumps” the recessive gene. • Carriers? • Table 3.2- Dark Hair/Blond, Curly/Straight, Dimples/no dimples, double-jointed/normal joints

  3. Chromosome and Gene-linked Abnormalities • Chromosome Abnormalities • Down syndrome- trisomy 21 • round face, flattened skull, extra skin over the eyelids, protruding tongue, short limbs, and motor and mental retardation. • 1/1900 @ 20 years; 1/45 @ 42 years

  4. Chromosome and Gene-linked Abnormalities • Chromosome Abnormalities • Down syndrome- trisomy 21 • round face, flattened skull, extra skin over the eyelids, protruding tongue, short limbs, and motor and mental retardation. • 1/1900 @ 20 years; 1/45 @ 42 years • Fragile X- Problem with the X-chromosome: often breaks • typically mental retardation • more frequent in males. Why? • 1/250 females are carriers vs. 1/800 males

  5. Chromosome and Gene-linked Abnormalities • Genetic Abnormalities • PKU- Phenylketonuria- Cannot properly metabolize the substance (phenylalanine). • mental retardation and hyperactivity if untreated. • “Curable” -Nature/nurture • Sickle-cell anemia- Deforms the body’s red blood cells • cells die causing anemia • Early death if left untreated.- Penicillin • 1/400 Af-Am babies born with • <1/10 Af-Am are carriers • 1/5 Africans

  6. Prenatal Screening • Dangerous- Why get it? • <3% of preg genetic abnormalities • 20% of infant deaths • Parents have family history of disease? Is mom/dad carrier? (Dominant”) • Does mother have any diseases? CMV-Cytomegalovirus • Are parents carries of a recessive sickle cell allele

  7. Prenatal Screening • Family History • Blood relatives with disorders • History of previous miscarriages • Children with specific genetic disorders • Members of at-risk group • Mother’s age and Father’s age • Behavior- Do parents use drugs/alcohol

  8. Prenatal detection • HCG-Human Chorionic Gonadotropin- Blood test- similar to a typical pregnancy test • Can determine an ectopic pregnancy • Sometimes combined with….

  9. Prenatal Detection • AFP- Alpha-fetoprotein- (also a Blood test) • looking for AFP being produced amniotic fluid and mothers blood. • Done at 15-20 weeks • Can determine if child has Down Syndrome (Decreased Levels)- though only in about 60% of cases • Can “help” determine neural tube defects such as spina bifida (Increased levels) • Fetal distress

  10. Prenatal Detection • Ultrasound- Standard of Care • Done at about 20-22 weeks • 2-D image using sound waves • Considered low-risk as long as non-repeated exposure- possible low birth weight • Doppler Ultrasound- 1 hour session- Color- Can look for signs of pre-eclampsia, poor blood flow.

  11. Other ultrasounds • http://www.youtube.com/watch?v=uo5gOWzgoaY • 4-D ultrasound

  12. Prenatal Detection • Amniocentesis • Done between 16th and 18th week though used to be done at 20th-22nd week. • Why the change???? • Takes two weeks to month to get results. • Needle through stomach, uterine wall, and amniotic sac, remove small amt of fluid • Avg. range=.3-.5%, but as high as 3-8% fetal loss • Risk of loss is greater than risk of birth defects in older moms • Can detect several hundred diff birth defects (out of 4000)

  13. Prenatal Detection • CVS- Chorionic Villi Sampling • Done at 10-12 weeks • Results take less than 10 days • Using ultrasound, take fetal cells from the chorion (placenta) • between a 0.5% and 1% risk of miscarriage • Slightly higher risk than amnio • Possible birth defects (1/3000)

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