Genetic Counselling and Genetic Testing - Part 2

Question 1

ultrasound

Answer 1

• ultrasound used to measure the thickness of the fluid buildup under the skin at the back of the baby’s neck
  (nuchal translucency )
• nuchal translucency + two serum markers can detect 90% of trisomy 21 Down syndrome

Question 2

amniocentesis

Answer 2

• under the guidance of an ultrasound, a sterile needle is inserted through the abdominal wall into the amniotic sac
• a small amount of amniotic fluid is withdrawn through the needle
• the amniotic fluid contains fetal cells, which are separated from the amniotic fluid and cultured
• tests are then performed on the cultured cells (chemical analysis, DNA analysis, chromosomal analysis)
• detects ~800 of the 5,000 known conditions

Question 3

chorionic villus sampling (CVS)

Answer 3

• CVS can be performed in early pregnancy
• under the guidance of an ultrasound, a catheter is inserted through the vagina and cervix into the uterus where it is placed into contact with the chorion, the outer layer of the placenta
• suction removes a small piece of the chorion
• cells of the chorion are used directly for many genetic tests, and culturing is not required
• cells that will form the placenta - same genotype as fetus
• karotyped directly, biochemical tests not possible
• slightly less accurate, higher risk of miscarriage (0.8% vs. 0.3% with amniocentesis)

Question 4

fetal cell sorting

Answer 4

• fetal cells can be sorted from maternal cells using fetal-specific cell surface markers and cell sorting
• zero risk to fetus

Question 5

pre-implantation genetic diagnosis (PGD)

Answer 5

individuals who are possible candidates for PGD:
- carriers of sex-linked genetic disorders
- carriers of single gene disorders
- those with chromosomal disorders
- women age 35 and over
- women experiencing recurrent pregnancy loss
- women with more than one failed fertility treatment

benefits:
- can test more than 100 different genetic conditions
- performed before implantation, allowing the couple to decide if they wish to continue with the pregnancy

concerns
- people believe the destruction of an embryo is the destruction of a person
- doesn’t completely eliminate the risk