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Genetic Testing. Flashcards

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1
Q

What is genetic testing used for?

A

To test embryos for genetic defects.

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2
Q

Who is tested in population screening?

A

These are tests that are given to any adults who are available to have them.

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3
Q

What are examples of population screenings?

A

PAP, breast and prostate exams.

These will test for various cancers and other problems.

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4
Q

What kind of pregnancy scans are included in population screening?

A

Prenatal screening or neonatal screening.

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5
Q

When does prenatal screening take place?

A

Before the baby is born.

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6
Q

When does neonatal screening take place?

A

After the baby is born.

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7
Q

Why does neonatal screening take place?

A

Because metabolic issues only show up after the baby has been born.

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8
Q

Who is tested in targeted screening?

A

All members of a population, regardless of their history.

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9
Q

What does targeted screening look for?

A

Diseases that can be passed down from a carrier to their offspring.

They are often common within certain populations

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10
Q

Tay Sachs disease is common in which population?

A

Ashkenazi Jewish population.

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11
Q

Thalessemia is common in people of what origin?

A

Mediterranean.

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12
Q

Targeted screening helps to identify what?

A

Carriers of a genetic disease.

This allows parents to determine how likely it is that their offspring will get the disease.

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13
Q

What are the 4 abnormalities that prenatal screening is used to detect?

A

Trisomy 21 (down syndrome).

Trisomy 18.

Trisomy 13 (similar to 18).

Neural tube defects.

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14
Q

Trisomy 21 is found in how many live births?

A

1/830 live births.

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15
Q

Trisomy 18 is found in how many live births?

A

1/7500 live births.

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16
Q

Trisomy 13 is found in how many live births?

A

1/22,700 live births.

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17
Q

Neural tube defects are found in how many live births?

A

1/2000 live births.

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18
Q

What is a process that allows for checking of the chromosomes?

A

Karyotyping.

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19
Q

What are non invasive methods of neonatal screening?

A

Maternal serum screening.

First trimester screen.

Second trimester screen.

Ultrasound (foetal anomaly scan).

Nuchal translucency.

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20
Q

What is the optimal time for detecting genetic defects using nuchal translucency?

A

11-14 weeks.

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21
Q

What is the optimal time for detecting genetic defects using ultrasound?

A

18 weeks.

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22
Q

What is the optimal time for detecting genetic defects using 2nd trimester scan?

A

14 weeks + 2 days - 20 weeks.

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23
Q

What is the optimal time for detecting genetic defects using 1st trimester scan?

A

11-14 weeks.

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24
Q

What is the optimal time for detecting genetic defects using maternal serum screening?

A

16 weeks.

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25
Q

If non invasive techniques show some abnormalities, what can couples do?

A

They can decide whether they want to do any further tests which involve invasive testing.

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26
Q

Is invasive testing better than non invasive testing?

A

Yes.

They will be more conclusive in telling whether the baby has any genetic defects.

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27
Q

What are the 2 invasive testing techniques?

A

Amniocentesis (amniotic fluid testing). 15-18 weeks.

Chronic villus sampling (placenta testing). 10-14 weeks.

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28
Q

What is the optimal time for amniocentesis?

A

15-18 weeks.

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29
Q

What is the optimum time for chronic villus sampling?

A

10-14 weeks.

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30
Q

What is amniocentesis?

A

Where 10-20mL of amniotic fluid is removed with a needle and the help of ultrasound.

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31
Q

Is amniocentesis done later or early in the pregnancy?

A

Late.

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32
Q

What are the ethical questions that a couple needs to answer if problems are found?

A

Whether it is ethical to do a late stage abortion.

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33
Q

What are the risks of miscarriage from amniocentesis?

A

0.5-1%.

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34
Q

What is chronic villus sampling?

A

The removal of foetal cells from the inner cell mass by a process called aspiration where a needle removes a part of the placenta with the help of ultrasound.

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35
Q

Which is done earlier, chronic villus sampling or amniocentesis?

A

Chronic villus sampling.

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36
Q

When is chronic villus sampling done?

A

At 11-12 weeks.

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37
Q

How are chromosomes taken via chronic villus sampling analysed?

A

Via FISH.

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38
Q

What is the risk of miscarriage associated with chronic villus sampling?

A

Around 1%.

Higher than amniocentesis.

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39
Q

What is maternal serum screening?

A

Where the pregnant mother will undergo a blood test.

Drs will look for markers that are abnormal such as human chorionic gonadotropin.

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40
Q

Is there more than 1 maternal serum screening?

A

Yes.

They will look for different factors and determine whether they are normal or abnormal.

Abnormal levels could indicate a difficulty in pregnancy.

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41
Q

What is tested for via maternal serum screening in the 1st trimester tests?

A

Pregnancy associated plasma protein.

Human chorionic gonadotropin.

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42
Q

When do the 1st trimester tests take place?

A

11-14 weeks + 1 day.

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43
Q

What are the 2 maternal serum screening tests in the 2nd trimester test?

A

Triple test.

Quad test.

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44
Q

What does the triple maternal serum screening test test for in the 2nd trimester test?

A

AFP (Alpha Foetal Protein). (Usually indicates neural tube defects).

Estriol. (Unconjugated estriol.)

Human chorionic gonadotropin.

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45
Q

What does the quad maternal serum screening test test for in the 2nd trimester test?

A

Inhibin A.

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46
Q

When is AFP detectable in foetal serum and when is it at peak levels?

A

At 6 weeks.

With peak levels at 12-14 weeks.

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47
Q

When is AFP detectable in the maternal blood and when are peak levels found?

A

After 14 weeks.

It will peak at around 16 weeks.

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48
Q

Where is AFP synthesised?

A

In the yolk sac.

Foetal GI tract.

Liver.

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49
Q

Lower than normal levels of AFP indicate what?

A

Down syndrome.

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50
Q

Higher than normal levels of AFP indicate what?

A

Spina bifida.

Very high levels indicate ancephaly.

51
Q

What are the abnormal levels of a 1st trimester scan if a baby has trisomy 21?

A

Nuchal translucency test = Raised.

PAPP-A = Raised.

HCG = Raised.

52
Q

What are the abnormal levels of a 1st trimester scan if a baby has trisomy 18?

A

Nuchal translucency test = Raised.

PAPP-A = Lower.

HCG = Lower.

53
Q

What are the abnormal levels of a 1st trimester scan if a baby has trisomy 13?

A

Nuchal translucency test = Raised.

PAPP-A = Lower.

HCG = Lower.

54
Q

What are the abnormal levels of a 1st trimester scan if a baby has neural tube defects?

A

Nuchal translucency test = Not detectable.

PAPP-A = Not detectable.

HCG = Not detectable.

55
Q

What are the abnormal levels of a 2nd trimester scan if a baby has trisomy 21?

A

Estriol (UE3) = Lower.

Alpha foetal protein. (AFP) = Lower.

HCG. (Human chorionic gonadotropin) = Raised.

Inhibin A = Raised.

56
Q

What are the abnormal levels of a 2nd trimester scan if a baby has trisomy 18?

A

Estriol (UE3) = Lower.

Alpha foetal protein. (AFP) = Lower.

HCG. (Human chorionic gonadotropin) = Lower.

Inhibin A = Not detectable.

57
Q

What are the abnormal levels of a 2nd trimester scan if a baby has trisomy 13?

A

Estriol (UE3) = Lower.

Alpha foetal protein. (AFP) = Lower.

HCG. (Human chorionic gonadotropin) = Lower.

Inhibin A = Not detectable.

58
Q

What are the abnormal levels of a 2nd trimester scan if a baby has neural tube defects?

A

Estriol (UE3) = Raised.

Alpha foetal protein. (AFP) = Not detectable.

HCG. (Human chorionic gonadotropin) = Not detectable.

Inhibin A = Not detectable.

59
Q

Low serum AFP, estriol and PAP A with high HCG indicates a risk for what?

A

Trisomy 21.

60
Q

Low serum AFP, estriol and PAPPA and HCG indicates a risk for what?

A

Trisomy 18 (Edwards syndrome) or trisomy 13 (Patau syndrome).

61
Q

Why is testing foetal DNA fragments in the mothers blood a good test?

A

It eliminates some of the risks of invasive testing.

62
Q

Where are foetal DNA fragments found for foetal DNA fragment testing?

A

In the mothers blood.

63
Q

What are foetal DNA fragments?

A

They are 25-30 base pairs long and can be matched to a specific chromosome.

64
Q

How do researchers detect an abnormality via foetal DNA testing?

A

They will count how many gene fragments came from each chromosome.

If there are more counts from chromosome 21, the baby has down syndrome.

65
Q

What can maternal serum screening detect?

A

80% of down syndrome cases.

80% of trisomy 18 cases.

80% of cases of spina bifida.

Over 90% of causes of anencephaly.

66
Q

If trisomy 21 or 18 are detected, how are they reported to the parents?

A

As a risk factor and not a diagnosis.

67
Q

Ultrasonography provides images of what?

A

The developing foetus and allows Drs to see any visible defects.

68
Q

What are 4 defects that can be detected by ultrasonography?

A

Neural tube defects.

Structural defects.

Rocker bottom foot.

Enlarged nuchal translucency.

69
Q

How are neural tube defects best detected?

A

By high levels of maternal AFP combined with ultrasonography.

70
Q

What are structural defects that can be detected by ultrasonography?

A

Missing digits, limbs etc.

Or defects such as cri du chat syndrome (micrognathia).

71
Q

What is rocker bottom foot often a sign of?

A

Edwards syndrome (trisomy 18).

72
Q

What is enlarged nuchal translucency?

A

Increased thickness is associated with chromosome aneuploidy and trisomy 21, 13 and 18 and also Turners syndrome.

73
Q

What is Turners syndrome?

A

When women are born with only 1 X chromosome.

74
Q

Where is the nuchal area?

A

Behind the neck of the foetus.

75
Q

What do prenatal genetic counsellors do?

A

Help and advise parents who have found out that their baby may have genetic defects.

Advise parents who are carriers of a certain disease about having children.

Warn about possible defects a person may carry thanks to origins.

Advise couples who have a history of infertility, miscarriages or stillbirths.

Advise couples older than 35.

Advise women with abnormal serum results.

Advise couples who have a child with a birth defect such as a neural tube defect.

Advise couples who have a child with a chromosomal abnormality or genetic disorder.

76
Q

Sickle cell anaemia is associated with people from what region?

A

Caribbean/Africa.

77
Q

Cystic fibrosis is associated with people from what region?

A

Northern Europe.

78
Q

Preimplantation genetics involves using what?

A

Artificial reproductive technology (ART).

79
Q

How does preimplantation genetics work?

A

The egg is fertilised via in vitro fertilisation.

The embryo is tested for genetic defects by removing and testing a cell.

If everything is ok, the cell is inserted into the mother.

80
Q

In preimplantation genetics, when is the cell removed for genetic testing?

A

At the 8-16 cell stage.

81
Q

Other than an embryonic cell, what else can be tested by preimplantation genetics?

A

Polar body’s.

82
Q

What are 9 common disorders that are tested for using preimplantation genetics?

A

Thalassemias.

Charcot Marie Tooth.

Cystic Fibrosis.

Huntingtons disease.

Myotonic dystrophy.

Rh.

Sickle cell anaemia.

Spinal muscular atrophy.

Tay Sachs disease.

83
Q

What are 8 less common disorders that are tested for using preimplantation genetics?

A

Adenomatosis polyposis coli (APC).

Epidermolysis bullosa.

Franconi anaemia.

Fragile X syndrome.

Gaucher disease.

Marfan syndrome.

Osteogenesis imperfecta.

Sanhoff disease.

84
Q

Why do scientists only have a limited amount of time when testing for disorders via preimplantation genetics?

A

They only have time to look for a limited number of disorders as the embryo needs to be inserted into the mother so it can implant.

85
Q

What does newborn screening look for?

A

Autosomal recessive disorders.

86
Q

Why is newborn screening done after birth?

A

As the baby will start to use its own metabolism.

87
Q

What do scientists look for in new born screening?

A

Direct biomarkers that are associated with a genetic illness.

88
Q

Give an example of an amino acid that can be tested for via neonatal screening?

A

High levels phenylalanine can indicate that it is not being metabolised.

If a baby tests positive for this test then Drs will remove phenylalanine from its diet.

89
Q

What is the main idea of newborn screening?

A

To look for diseases that Drs can fix before the disease starts to affect the infant.

90
Q

Many of the diseases tested for in newborn screening will create what in later life if they are left untreated?

A

Irreversible damage.

91
Q

What are the 4 criteria for neonatal testing?

A

Drs will look for a disorder that produces irreversible damage if left untreated.

There must be treatment available for the disorder.

Early intervention against the disease must be effective.

Tests for detection must be reliable and positive tests are always re-tested.

92
Q

New born screening skips what parts of normal medicine?

A

The identification of symptoms.

Diagnosis.

Treatment.

93
Q

What do Drs need to take from the baby for newborn screening?

A

A drop of blood.

94
Q

What machine is used for newborn screening?

A

An MS/MS system (tandem mass spectrometer).

95
Q

What is an old test used for newborn screening?

A

Guthries inhibition assay.

96
Q

How is an abnormal amount of an amino acid detected using Guthries inhibition assay?

A

There will be a large spike indicating the abnormal amino acid.

97
Q

What happens to the blood spot as it goes through the mass spectrometer?

A

It is ionised and placed inside the 1st spectrometer which will fragment selected ions.

These are separated by the 2nd mass spectrometer and amino acids are detected.

98
Q

How are the amino acids detected in the spectrometer?

A

By their signature fragment pattern.

99
Q

Phenylketonuria is caused by what?

A

High levels of phenylalanine in the bloodstream.

100
Q

What are the symptoms of untreated phenylketonuria?

A

Mental retardation, behaviour problems and convulsions.

101
Q

What are the 5 ways that can be used to detect Sickle Cell anaemia?

A

Haemoglobin electrophoresis.

DNA testing.

Southern blot technique.

RFLP.

ASO.

102
Q

What causes sickle cell anaemia?

A

A point mutation in beta-globin.

103
Q

How is sickle cell treated?

A

by preventing a sickling crisis and by blood transfusions of hydroxyurea.

104
Q

Alpha and beta thalassemia show what form of inheritance?

A

Autosomal recessive inheritance.

105
Q

How can alpha and beta thalassemia be detected?

A

By calculating the mean corpuscular haemoglobin.

By haemoglobin electrophoresis.

106
Q

Screening for carriers has significantly reduced alpha and beta thalassemia in what countries?

A

Cyprus and Greece.

107
Q

What causes cystic fibrosis?

A

A mutation in the CF transmembrane conductance regulator (CFTR).

108
Q

How is cystic fibrosis detected?

A

By inserting an immune reactive trypsinogen (IRT) into the blood, followed by a DNA test.

109
Q

What is the confirmatory test for cystic fibrosis?

A

The sweat chloride test.

110
Q

How many mutations of cystic fibrosis are due to delta F508 mutations?

A

70-80%.

111
Q

How can cystic fibrosis be managed?

A

With antibiotics to combat respiratory infections.

It can be managed further by gene therapy and by managing associated malabsorption.

112
Q

When do most couples learn that they are carriers of a disorder?

A

After they have given birth to an affected child.

113
Q

Ashkenazi Jewish populations are high carriers of what disease?

A

Tay Sachs/Gaucher disease (1/29 carrier frequency).

114
Q

Caucasians are high carriers of what disease?

A

Cystic fibrosis.

115
Q

Mediterranean/Asian are high carriers of what disease?

A

Thalassemia.

116
Q

Africans are high carriers of what disease?

A

Sickle cell.

117
Q

What are the options for a couple who are both carriers?

A

Choose not to have children.

Artificial insemination or egg donation.

Prenatal diagnosis and termination of an affected pregnancy.

Prenatal diagnosis and planning for the care of an affected child.

No prenatal testing (potluck).

118
Q

Can a carrier of a disease be designated as a non carrier?

A

Yes, if they are carrying a rare mutation.

119
Q

What does genetic counselling help families to do?

A

Understand and adapt to the medical, psychological and familial implications of genetic contributions to disease

120
Q

What do genetic counsellors do if a person has a genetic disorder?

A

Inform the infected individual and their family.

Tell the individual about the characteristics of the disorder.

Identify the risk of the individual passing the disorder on to their children.

Tell sufferers how to live as best they can.

121
Q

What are the most common issues in genetics?

A

Autonomy.

Informed choice.

Informed consent.

Confidentiality.

122
Q

What is the idea of genetic counselling?

A

Not to tell patients what to do, but to give them enough information so that they can make an informed decision.

123
Q

What do genetic counsellors do?

A

Interpret family and medical histories to asses the chance of disease occurrence in offspring.

Educate people about the importance of inheritance, testing, management, prevention, resources and research.

They will help people to make informed choices and adapt to life with a condition.

124
Q

What are some ethical dilemmas associated with genetic testing?

A

Abortion.

Expensive surgeries.

Health insurance increase.

Refusal of health insurance.

Children not being covered by insurance.

Developmental Biology. (21 decks)

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