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Genetics > Genetic Testing > Flashcards

Genetic Testing Flashcards

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1
Q

What happens in the normal pregnancy

A

Positive pregnancy test - no longer confirmed at GP

Book in antenatal care - where you give birth

Nuchal scan - e.g. nuchal translucency, combined test

Anomaly scan at 20 weeks

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2
Q

What happens during a nuchal scan

A

12 weeks of pregnancy

Genetic risk

Blood done

Scan - nuchal fold, measurement at the baby’s neck

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3
Q

What is the aim of the 12 week scan

A

Date pregnancy

Diagnose multiple pregnancy

Major fetal abnormalities

Early miscarraige

Asses the risk of down syndrome

Take into account maternal age, blood hormone, nuchal translucency thickness, nasal bone, blood flow and fetal abnormalities

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4
Q

What is nuchal Translucency

A

Thickness of fluid at back of fetal neck

Increased >3mm can indicate chromosome problem

Chromosome abnormalities (downs)

Birth defects: cardiac anomalies, pulmonary, renal

Skeletal dysplasias

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5
Q

Is NT screening test or diagnostic test

A

NT is a screening test

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6
Q

When is prenatal testing arranged

A

Abnormal findings at nuchal scan or mid trimester scan

Results of combined test which give increased risk of Down Syndrome

Previous pregnancy affected, DS, CF

Parent is carrier of chromosome, DMD, HD

Family history of genetic condition

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7
Q

Aims of Prenatal Testing

A

Inform and prepare parents

In utero treatment

Manage remainder of pregnancy

Prepared for complications of birth

Termination

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8
Q

What other fetal scans can you do

A

Fetal MRI - look at organs clearly

Fetal cardiac scan - flow of blood

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9
Q

What is cell-free fetal DNA

A

Floating around mother’s blood

DNA from baby placenta shed into mother’s bloodstream

Detectable from 4-5 but accurately detected at 9 weeks

Non invasive

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10
Q

What test for NIPD (non invasive prenatal diagnosis)

A

20ml

Achondroplasia, thanatophoric dysplasia, apert syndrome

Male and Female fetus SRY gene on Y chromosome

DMD may have to be organised if boy

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11
Q

What are NIPD offered privately via NHS

A

Autosomal dominant single gene disorders inherited from the father

Test will detect paternal mutation - if inherited go on to do invasive

CF - can test for maternal and paternal

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12
Q

cffDNA testing for Aneuploidy (NIPT)

A

Aneuploidy - extra chromsome 21, 18, 13

Offered privately

Non invasive test

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13
Q

Limitations of NIPD and NIPT

A

Multiple pregnancies

Cell free fetal DNA reduced in women with higher BMI - second sample may be needed

Do women want the information

An invasive test may still be required to confirm an abnormal result

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14
Q

Benefits of NIPD and NIPT

A

Number of invasive test

No increased risk of miscarriage

Less expertise

Offer NIPD earlier than traditional invasive testing

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15
Q

What are the invasive test

A

Chorionic villus sampling (CVS)

Amniocentesis

Molecular, cytogenetic and biochemical tests

Ultrasound guidance

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16
Q

What happens in Chorionic Villus Sampling

A

11-14 weeks

1-2% risk of miscarriage

Transabdominal or transvaginal

Sample of chorionic villi - part of developing placenta - same DNA as fetus

Allows patient to have earlier result that amnio - TOP decision

17
Q

What happens in amniocentesis

A

From 16 weeks

Sample of amniotic fluid

1% risk of miscarriage

Infection

Rh sensitisation

18
Q

What tests are done with the DNA sample

A

Test for genetic disorder in quesiton - CF

Karyotype if chromosomal abnormality in family - 2 week results

QF-PCR - t13, 18 and 21 which are reported in 24-48

19
Q

What is the CGH array

A

Small/arge imbalances in chromosomes

Concerns on 20 week scan

If something is found, we test parents - interpretation

Neurosusceptibility

20
Q

What is trio exome

A

Considered when fetus in previous pregnancy had significant anomalies

Exome region of DNA look - take DNA from baby and parents

May not prduce answer the parents are hoping for

21
Q

Reproductive options

A

Conceive naturally with or without prenatal testing

Egg and sperm donors

Adoption

Pre-implantation genetic diagnosis

22
Q

Facts about egg and sperm donation

A

No longer anonymous, children conceived have right to contact donor when 18

Go through UK HFEA licensed fertility centre - legal standards

Privately find donor

Go abroad

23
Q

Adoption

A

Registration and checks - interest, medical and criminal background, 2 months

Assessment and approval - home visits by social worker, prospective adopters report given to panel, panel review information, 4 months

24
Q

What happens during preimplantation genetic diagnosis

A

Uses IVF which geneticlaly test embryo before implantation

People who don’t want TOP

25
Q

Process of PGD

A

Stimulation of ovaries - hyperstimulation

Egg collection

Insemination

Fertilisation

Embryo biopsy - blastocyte stage, one cell taken away

Embryo testing

Embryo transfer

Pregnancy test

26
Q

What is the process of intracytoplasmic sperm injection

A

Single sperm injected into centre of each egg

no contamination of other sperms

27
Q

Where is PGD avaliable

A

UCH

Guys hospital

13000,12000

28
Q

What is PGD used for

A

Translocation carriers

HD

DMD

CF

29
Q

What is the eligibility criteria for PGD

A

Female under 39

BMI of 19-30

Non smokers

Living together over a year

No living unaffected children

Know risk of having a child affected by genetic condition (10%)

Femal partner hormone levels will respond to treatment

Accurate genetic test is available

No welfare concerns for unborn child

Licence required from HFEA

Funded for three rounds of PGD

30
Q

Role of genetic counselling

A

Arrange CVS, amniocentesis, PGD, cffDNA

Facilitate decision-making

Give results

See patients in clinic

Arrange termination

Discuess recurrence risks and plans for future pregnancies

31
Q

How do you facilitate decision making

A

Previous experience, family situation, religion, personal beliefs, psychosocial situation, balancing miscarriage risk with genetic risk, dealing with indecision

Genetics (9 decks)

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