Genetic Screening

Question 1

contrast targeted screening and population screening

Answer 1

• targeted screening
  
  • screening of populations known to be at risk
  • screening of high risk ethnic groups (Tay-Sach’s, thalassemia)
  • identifying persons at risk of having children w/ disease
• population screening
  
  • adult screening that is presymptomatic/predictive
    
    • PAP, breast, prostate
  • screening all members of a designated population regardless of family history

Question 2

describe what is looked for in first trimester tests

Answer 2

• pregnancy associated plasma protein-A (PAPP-A)
• B-hCG

Question 3

describe what is looked for in second trimester tests

Answer 3

• triple test:
  
  • AFP
  • estriol
  • B-hCG
• quad test:
  
  • inhibin A

Question 4

describe results of first and second trimester screening

Answer 4

• trisomy 21 = increased free B-hCG and increased inhibin A
• trisomy 18 = trisomy 13
• neural tube defect = increased AFP

Question 5

describe fetal DNA fragments

Answer 5

• fetal DNA fragments are matched to a specific chromosome and researchers tally how many gene fragments originated from each chromosome
• women with Down syndrome had more fetal chromosome 21 fragments in their blood than normal

Question 6

describe nuchal translucency

Answer 6

• increased NT thickness associated with chromosome aneuploidy
  
  • trisomy 21, 18. 13. Turner syndrome

Question 7

describe chorionic villus sampling

Answer 7

done at 11-12 weeks

• involves removal of fetal cells by aspiration from inner surface of placenta
• direct chromosomal analysis by FISH allows rapid results

Question 8

describe amniocentesis

Answer 8

15-18 weeks

• aminiotic fluid aspirated trans-abdominally guided by ultrasound
• fetal cells pelleted by centrifugation and used for chromosome analysis

Question 9

describe criteria for neonatal screening

Answer 9

• the disorder produces irreversible damage if untreated early in life
• there is a treatment available for the disorder
• early intervention is effective
• a reliable lab test for detection

Question 10

describe what an amino acid profile from a patient with PKU would look like

Answer 10