Genetics and Prenatal Screening

1. Genetics and Prenatal Screening

3. 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

5. 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

7. 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

8. 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

9. 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

10. 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

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

12. 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

13. 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.

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

16. 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)

17. 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)