Antenatal and Postnatal Screening

Question 1

What is a screening test ?

Answer 1

-Used to detect signs and symptoms associated with a certain condition or disorder.

-If signs are found, the probability that the individual is suffering the condition can be assessed as a degree of risk.

-A variety of techniques can be used to monitor the health of the mother and developing foetus and baby.

Question 2

What are the types of screening ?

Answer 2

1) Antenatal screening
2) Postnatal Screening

Question 3

What is antenatal screening ?

Answer 3

-Pre-birth (in pregnancy) screening, identifies the risk of a disorder so that further tests and a prenatal diagnosis can be offered.

Question 4

What is postnatal screening ?

Answer 4

Postnatal screening is after birth screening which can diagnose metabolic or genetic disorders in the baby

Question 5

What are the antenatal screening techniques ?

Answer 5

1) Ultrasound Imaging
2) Biochemical Tests
3) Diagnostic Tests

Question 6

What is ultrasound imaging ?

Answer 6

An antenatal screening technique - high frequency (20,0000 MHz) sound waves bounce off foetus, converted into an ultrasound image on a computer screen.

Question 7

What types of ultrasound scans are pregnant women given ?

Answer 7

1) A dating scan
2) An anomaly scan

Question 8

What is the purpose of the dating scan ? and state the timing of this scan.

Answer 8

-Dating scan determines the stage of pregnancy and due date.
-Takes place between weeks 8-14 of pregnancy.

Question 9

What is the purpose of the anomaly scan ? and state the timing of this scan.

Answer 9

-Anomaly scan detects serious physical abnormalities in the foetus.
-Takes place between weeks 18-20 of pregnancy.

Question 10

What is biochemical testing ?

Answer 10

An antenatal screening techniques - (blood and urine tests)
-Routine blood and urine tests are carried out throughout pregnancy to monitor the concentration of marker chemicals.
-The results of these tests are used alongside dating scans to check whether the concentration of marker chemicals follow the typical changes expected during a pregnancy.

An atypical chemical concentration can lead to diagnostic testing to determine if the foetus has a medical condition.

Question 11

What can cause as false positive result (biochemical testing) ?

Answer 11

Measuring a chemical at the wrong time could lead to a false positive result.

Question 12

What is a false positive result (biochemical testing) ?

Answer 12

False-positive test results indicated that person has a specific condition when the persona actually does not have it.

Question 13

What are the consequences of sharing a false positive result ?

Answer 13

1) Causes anxiety.
2) Additional diagnostic tests carry risks of miscarriage.
3) Parents may unnecessarily terminate the pregnancy.

Question 14

What is diagnostic testing ?

Answer 14

-An antenatal screening technique

-A definitive test that produces results that can be used to establish without doubt if the person is suffering from the condition or not (Amniocentesis & CVS)

Question 15

When should a woman be offered diagnostic tests ?

Answer 15

1) Potential problems detected in early screening tests.
2) Family history of a harmful genetic disorder.
3) Woman belongs to a high-risk category (>35 years old)

Question 16

What does a karyotype show ?

Answer 16

-Diagram showing chromosomes lined up in their homologous pairs.
-Cells from tissue samples can be cultured to obtain sufficient cells to produce a karyotype to diagnose a range of conditions.

(Used as diagnostic testing)

Question 17

How are the cells needed to obtain a karyotype gained ?

Answer 17

1) Amniocentesis
2) Chronic villus sampling (CVS)

(Used as diagnostic screening)

Question 18

What is amniocentesis ?

Answer 18

A method to gain the cells needed to obtain karyotype (used as diagnostic testing)
-Foetal cells are extracted from the amniotic fluid.
- Foetal cells are cultured, stained and their karyotype examined.

Question 19

What is chronic villus sampling ?

Answer 19

A method to gain the cells needed to obtain karyotype (used as diagnostic testing)
- Foetal cells are extracted from the placenta.
-Foetal cells are cultured, stained and their karyotype examined.

Question 20

What are advantages and disadvantages of amniocentesis ?

Answer 20

Advantages = Test carries a lower risk of miscarriage (0.5%)

Disadvantages = Test carried out between weeks 14-16, results take longer to obtain (2 weeks)

Question 21

What are advantages and disadvantages of chronic villus sampling ?

Answer 21

Advantages = Test carried out as early as 8 weeks, results established quickly

Disadvantages = test carries a higher risk of miscarriage (2%)

Question 22

Describe decision making in diagnostic testing

Answer 22

In deciding to proceed with these tests (amniocentesis and CVS), the element of risk will be assessed, as will the decisions the induvial concerned are likely to make if a test is positive.

Question 23

What is a postnatal screening technique ?

Answer 23

A postnatal screening technique is diagnostic for metabolic disorders.
-Phenylketonuria (PKU) is a metabolic disorder caused by a substitution mutation, leads to a build up of phenylalanine (toxin) to affect brain cells and limits mental development.
-The enzyme cannot break down phenylalanine to tyrosine.
-In the UK, babies are routinely checked for excess phenylalanine in the first few days of birth using a heel-prick test.

Question 24

How are PKU suffered treated ?

Answer 24

Individuals who suffer from PKU are placed om a restricted, low-protein, diet.

Question 25

What are the categories of postnatal genetic disorders ?

Answer 25

Sex-linked or autosomal

Question 26

What is a sex-linked disorder ?

Answer 26

Type of postnatal genetic disorder
-Associated with sex chromosomes (pair 23) (X or Y)

Question 27

What is an autosomal disorder ?

Answer 27

Type of postnatal genetic disorder
-Associated with autosomes (pairs 1-22)

Question 28

What is a pedigree chart ?

Answer 28

A family tree which can reveal a pattern of inheritance. Phenotypes are known then genotypes calculated.

Question 29

What is genetic counselling ?

Answer 29

-A genetic counsellor would construct a pedigree chart to reveal patterns of inheritance - this is done when a couple are worried about the possibility of passing on a genetic disorder to their children.

Question 30

How do you know is you are at risk of a particular genetic disorder ?

Answer 30

-DNA sequences that increase the risk of a particular disease can be identified using genetic sequencing.
-The results obtained may differ from the predicted results as fertilisation is a random process with an element of chance.

Question 31

What are the traits of an autosomal recessive disorder ?

Answer 31

1) Relatively rare (may skip generations)
2) Individuals can carry the condition without being affected
3) Effects males and females in equal numbers.

Sufferers must be homozygous recessive

An example of an autosomal recessive disorder is Cystic Fibrosis

Question 32

What are the traits of an autosomal dominant disorder ?

Answer 32

1) Relatively common (affects every generation)
2) Individuals cannot carry the condition without being affected.
3) Effects males and females in equal numbers.

Sufferers only need one dominant allele to be affected (Homozygous dominant/Heterozygous)

An example of an autosomal dominant disorder is Huntington’s chorea

Question 33

What is an autosomal incomplete dominant disorder ?

Answer 33

-Neither allele is completely dominant over the other.
-A heterozygous individual person will have a blend of the two homozygous types.

Question 34

What are the traits of an autosomal incomplete dominant disorder ?

Answer 34

1) Full expression of the disease is rare
2) Partial expression of the disease is more common
3) Effects males and females in equal numbers.

Sickle cell anaemia is an example of a human disorder controlled by incompletely dominant alleles.

Question 35

What rules can the geneticist apply when adding genotypes to a family tree for autosomal dominant inheritance ?

Answer 35

-All non-sufferers must be homozygous recessive (hh)
-Sufferers are homozygous dominant (HH) or heterozygous (Hh)

Question 36

What rules can the geneticist apply when adding genotypes to a family tree for autosomal incomplete dominant inheritance ?

Answer 36

-All non-sufferers must be homozygous for one incompletely dominant allele (e.g AA)
-Sufferers are homozygous of other dominant allele (e.g SS)
-Partial must have one of each (e.g AS)

Question 37

What are the traits of a sex-linked disorder

Answer 37

1) Associated with genes found only on the X chromosome.
2) Males cannot pass the condition to their son.
3) Effects more males than females.

Question 38

What are alleles

Answer 38

Different forms of a gene

Question 39

What does homozygous mean, in terms of genotype?

Answer 39

The genotype of a homozygous individual consists of two identical alleles e.g HH or hh

Question 40

What does heterozygous mean, in terms of genotype?

Answer 40

The genotype of a heterozygous individual consists of two dissimilar alleles e.g Hh