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Genes and early embryology > Obstetric genetics > Flashcards

Obstetric genetics Flashcards

1
Q

What are the different types of inheritance

A
  • autosomal dominant
  • Autosomal recessive
  • x-linked recessive
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2
Q

Whats autosomal dominant inheritance

A

Heterozygous with one copy of abnormal gene are affected

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3
Q

Whats autosomal recessive inheritance

A

`homozygous with two copies of the abnormal gene are affected

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4
Q

Whats x-linked recessive inheritance

A

Males which one copy of the abnormal gene on X-chromosome are affected

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5
Q

Who is not affected by x-linked inheritance

A

Carrier women

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6
Q

Who can’t x-linked inherited genes be passed on from-to

A

Male to male

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7
Q

Who are affected by x-linked recessive diseases

A

All men who inherit the mutation

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8
Q

Examples of x-linked diseases

A
  • Haemophilia

- Duchene muscular dystrophy

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9
Q

common examples of recessive inherited diseases

A
  • CF
  • Haemochromatis
  • Beta thaloesemia
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10
Q

What’s the chance of being a carrier when you are not affected, but your sibling is

A

2/3

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11
Q

Formula for risk

A

Risk in A x Risk in B x Probability that child will inherit 2 copies of the mutation

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12
Q

What formula do you use when you don’t know the carrier rate

A

Hardy Weinburg (as long as the gene frequency is in equilibrium)

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13
Q

When is chronic villus sampling done

A

11-13 weeks

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14
Q

How is chronic villus sampling done

A

needle stuck through stomach and chromosomes are tested

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15
Q

risks of chronic villus sampling

A

1% risk of miscarriage

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16
Q

When is amniocentesis done

A

15-16 weeks

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17
Q

Where are amniocytes derived from

A

Fetal tissue and amnion

18
Q

How long does chromosome analysis in amniocentesis take

A

2-3 weeks

19
Q

Negatives of amniocentesis

A

Low yield of fetal DNA, 1% miscarriage

20
Q

What happens in PGD

A

1) stimulation ovulation
2) oocyte retrieval
3) fertilization and culture
4) blastocyst biopsy on day 5

21
Q

When does transfer of embryos occur in PGD

A

embryos are frozen when testing takes place and the transfer of embryo occurs 2 months later

22
Q

What is the live birth rate of PGD

A

35%

23
Q

What gives a persons liability to be affected?

A

Sum of environmental and genetic predisposition

24
Q

What is recurrence risk

A

Empiric figures from population studies

25
Q

Rules for recurrence relation in multifactorial inheritance

A
  • people who have relatives with the condition have curve shifted to the right so more individuals cross the threshold
  • risks bigger for close relatives
  • Risks greater if relative is more severely affected
  • risk higher if more than one relative is affected
  • Someone with a high genetic liability will not be affected if the environment is favorable
  • risk higher if a child of the lower risk gender is affected in the family. (i.e. autism more prevalent in boys so if female in family has it, then you are more likely to get it)
26
Q

What are the screening tests offered in a routine pregnancy

A
  • scans

- trisomy screening

27
Q

When is an ultrasound done

A

8+ weeks

28
Q

When is an NT scan done and what does it detect?

-what does an increased NT caused by

A

Measures width of back of babies neck

increased NT caused by:

  • downs syndrome
  • major congenital heart disease
29
Q

When is biochemical serum screening

A

10-14 weeks detects beta HCG and PAPP-A

second trimester detects afp, estriol and beta HCG

30
Q

Abnormal MSAFP levels and what do they indicate

A

<0.5 = down’s

>2.5+ neural tube defect, missed or threatened miscarriage, multiple pregnancy

31
Q

When is the second ultrasound done

A

18-20 weeks (fetal anomaly scans)

32
Q

Whats cardocentesis

A

Checking the fetal blood (invasive)

33
Q

What does universal newborn screening check for

A
  • CF
  • PKU
  • Sickle cell
  • MCADD
34
Q

What is polygenic inheritance

A

Effect of many genes

35
Q

What affects polygenic inheritance

A

Genes at many loci

36
Q

Example of polygenic inheritance

A

Height

37
Q

What has an impact on all polygenic inheritance

A

environment

38
Q

What are the rules for the effect on environmental polygenic iheritance

A
  • relatives of an affected person have got a greater genetic tendency
  • Risks are greatest for close relatives
  • Risks greater for relatives when the person is more seriously affected
  • Risk higher if more people are affected
  • If there are conditions which affect one gender more (i.e. boy), and a girl in family is affected you are more likely to get it
39
Q

How to reduce recurrence risk of neural tube defects

A

folic acid

40
Q

Congenital example of multifactorial inheritance

A
  • cleft lip
  • congenital heart defect
  • Talipes
41
Q

Adult onset disorders of multifactorial inheritance

A
  • Diabetes mellitus
  • EPilepsy
  • Glaucoma

Genes and early embryology (12 decks)

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