testing for genetic disorders

Question 1

the purpose of prenatal screening

Answer 1

guides family in decisions around pregnancy

• might involve termination
• facilitate medical and psychological support

Question 2

screening tests

Answer 2

assess risks but not diagnostic test
e.g. maternal serum for down syndrome
are non-invasive, low-risk tests

Question 3

what are diagnostic tests looking for

Answer 3

testing for a specific chromosomal or genetic abnormality
e.g. gene mutation analysis for cystic fibrosis
invasive test, carriers some risks

Question 4

indications for prenatal testing

- for single gene disorders

Answer 4

• family history
• both parent carriers
• female carrier (x-linked)
• one parent has autosomal dominant disorder
  only consider with serious disorders

Question 5

indications for prenatal testing

- for constitutional chromosomal disorders

Answer 5

• older mother pregnant
• previous child with congenital disorder
• exposure to chemical or toxic agent
• abnormal screening test

Question 6

ultrasound scanning

Answer 6

Commonly used for screening test, can be a diagnostic test but rarely
do risk to mother or fetus

Question 7

nuchal translucency

Answer 7

• measured in an ultrasound
• is the depth of fluid at the back of baby’s neck
• is a screening test that calculates the risk of having down syndrome child
• non-invasive test

Question 8

maternal serum testing

Answer 8

looks at placental-related proteins

• non-invasive
• is a screening test that calculates the risk of having down syndrome child or NTDs
• risk prediction test

Question 9

screening tests

Answer 9

• ultrasound
• nuchal translucency
• maternal serum testing

Question 10

when the risk prediction for down syndrome is high what diagnostic tests may be carried out

Answer 10

amniocentesis

karyotype analysis

Question 11

Diagnostic tests

Answer 11

Chorionic villus sampling (CVS)

amniocentesis

Question 12

Chorionic villus sampling

Answer 12

• can be done early in the pregnancy
• done under ultrasound guidance
• obtain fetal cells
• 1% risk of miscarriage

Question 13

Amniocentesis

Answer 13

• later in pregnancy
• done under ultrasound guidance
• collect fluid which contains fetal cells
• may need to culture cells before analysis
• 1% risk of miscarriage

Question 14

differences between CVS and amniocentesis

Answer 14

CVS - get enough cells to analyze (karyotype) straight away, therefore, parents get results early in pregnancy

amniocentesis - fetal cells need to be cultured in lab which can take several weeks

Question 15

issues to consider when testing

Answer 15

non-comprehensive testing

• only tests for common chromosomal disorders
• need to know mutation of single gene disorders
• the risk of error

risk to the fetus

not morally or ethically accepted

Question 16

potential benefits of prenatal testing

Answer 16

• reassurance when results are normal
• psychological preparation for the arrival of affected baby
• advanced warning for medical team
• provide information for parents where termination may be an option

Question 17

preimplantation genetic diagnosis

Answer 17

• where IVF is used to conceive a child

- before being implanted embryos are analyzed, then normal karyotype implanted

Question 18

importance of counseling

Answer 18

• provides up to date information

- opportunity to discuss advantages and disadvantages of having screening or diagnostic test