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GEN > Genetics in Clinical Practice 2 > Flashcards

Genetics in Clinical Practice 2 Flashcards

1
Q

What are the 2 types of genetic consultation?

A
  1. Diagnostic

2. Pre-symptomatic testing (Predictive)

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2
Q

What does diagnostic genetic consultation involve?

A

Clinical assessment, investigations, counselling, implications for affected person and family members

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3
Q

Who is predictive testing for?

A

Indiv at risk based on family history, usually for adult onset cond

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4
Q

What is genetic counselling?

A

Comm of nature of genetic disorder

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5
Q

Why is genetic counselling important?

A

Discuss risks of transmission/inheritance/penetrance of future pregnancies on basis of family history and support in making informed decisions

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6
Q

What is clinical diagnosis based on?

A

Clinical (dysmorphic) features

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7
Q

List the genetic tests

A
  • Standard chr analysis
  • FISH
  • Array CGH
  • Single gene testing
  • Next Gen Sequencing
  • Methylation analysis (imprinting disorders)
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8
Q

What are the indications for genetic tests?

A
  • Multiple problems (structural abn, dev delay)

- Often unusual combo, unless recognised syndrome

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9
Q

What have basic genetic tests been replaced by?

A

Array CGH

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10
Q

What is VACTERL association?

A

Non-random association of birth defects that affects multiple body systems

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11
Q

What does VACTERL association stand for?

A 
Vertebral
Anal Atresia
Cardiac
Tracheo-oEsophageal atresia/phistula
Renal abnormalities
Limb (radial ray defect)
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12
Q

What does Array CGH identify?

A

V. small genomic imbalances which may have effect on indiv’s health + dev/inc susceptibility to certain cond e.g. ASD, psychiatric disease, congenital abnormalities

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13
Q

What disorders can deletion of chr 16 lead to?

A

Learning diff
Bipolar
Obesity in young adults
Lower IQ

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14
Q

What is single gene testing used for and why?

A

Diagnosis/conformation of genetic disorders
Test (carrier/pre-symp) for at risk relatives
Can facilitate management + get accurate recurrence risk

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15
Q

What rep options can be considered from results of single gene testing?

A
  • Prenatal diagnosis

- Pre-implantation genetic diagnosis

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16
Q

What are the recurrence risks for achondroplasia for affected and unaffected parents?

A

Unaffected - 1%

Affected - 50%

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17
Q

What is Next Generation Sequencing?

A

Test whole genome for no. of genes that may be rel to phenotype

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18
Q

What does genetic diagnosis allow?

A
  • Confirm clinical diagnosis
  • Dec need for other investigations to get diagnosis
  • Only diagnostic in some cases
  • May help prognostication
  • Gene based therapies (rare)
  • RR assessment
  • Informed choice in future pregnancies
  • Pre-symptomatic testing
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19
Q

Why are chr rearrangement tests needed?

A

Need tests to detect rearrangements at diff level res

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20
Q

What are aneuploidies and 3 e.g.s?

A

Chr no. not div by 23

E.g. Down’s (trisomy 21), Patau (13), Edwards (18)

21
Q

What are polyploidies?

A

Multiple sets of 23 chr

22
Q

What are balanced chr structure (translocations)?

A

2 chr break + swap places without losing gen material/interfering with gene at specific break point

23
Q

Name e.g.s of unbalanced chr structure

A
  • Deletions
  • Duplications
  • Inversions
  • Translocations
24
Q

Define Deletions

A

Part of chr missing

E.g. Cri du Chat (chr 5 missing)

25
Q

Define Duplications

A

Part of chr duplicated/present in 2 copies

26
Q

Define Inversions

A

Chr breaks + rearranges itself so segment is reversed

27
Q

Define Translocations

A
  • 2 types:
    1) Reciprocal = 2 diff chr exchanged segments
    2) Roberstonian = entire chr attaches at centromere to another chr
28
Q

What are the complications of Turner Syndrome?

A
  • Peripheral oedema at birth
  • Short stature
  • 1 degree amenorrhoea (streak ovaries)
  • Normal intelligence
29
Q

What is a risk figure needed for?

A

Adult onset cond

Offspring and family member risk

30
Q

What does accurate estimation of risk require?

A

Confirmation of diagnosis

Accurate family tree

31
Q

What do genetic tests help to do?

A

Refine risk
Give options
Management

32
Q

What is risk to offspring (RR) of autsomal dom cond of affected M + unaffected F?

A
  • 1 in 2 with equal probab from carrier parent
33
Q

What is neurofibromatosis 1 an e.g. of?

A

A cond where various phenotype which abnormalities characterise cond are v. variable

34
Q

How is risk of affected child calc for autosomal dom cond with incomplete penetrance?

A

Probab of inheriting mutant allele x penetrance

35
Q

In e.g. of retinoblastoma (dom) with penetrance: 0.8/80% (meaning 80% dev cond), what is risk of affected child?

A

1/2 x 0.8(4/5) = 0.4 (4/10)

36
Q

What is risk of affected sons, daughters being carriers, and unaffected sons of X-linked cond with normal M + carrier F parents?

A
  • 1 in 4 affected sons
  • 1 in 2 daughters carriers
  • 1 in 2 sons unaffected
37
Q

Why are only M affected in X-linked inheritance?

A

M don’t have spare X

38
Q

What is risk of affected offspring and carrier risk of unaffected siblings of autosomal rec cond and why?

A
  • affected: 1 in 4

- carrier risk is 1 in 2 at conception but becomes 2 in 3 if siblings of rec cond clinically unaffected

39
Q

What does the Hardy-Weinberg equation help to explain?

A

Gene freq in pop + useful for calc risks of autosomal rec disorders

40
Q

What does p + q mean in HWE?

A

p = freq of wild type allele
q = freq of rec allele
- rep prop of chr which have allele not no. of people who carry allele

41
Q

If we have 2 alleles A + a, what are the ratios of the diff genotypes and their freq?

A

AA - p2
Aa - 2pq (2 bc there are 2 offspring with Aa in punnet square)
aa - q2

42
Q

What does allele freq at a locus add up to and the equation?

A

1

p + q = 1

43
Q

What does genotype freq sum to and the equation?

A

1

p2 + 2pq + q2

44
Q

How do you calc allele freq for rec allele?

A

disease incidence = q2

freq of rec allele = square root of q2 = q

45
Q

What does carrier freq (2pq) not equal and when does it change?

A

Rec allele freq (q) but approx to 2q when q small (most cases

46
Q

Calc risk of CF to couple’s offspring (e.g. from lecture)

CF incidence: 1 in 2500

A

q2 = 1 in 2500
q = square root 1/2500 = 1/50
carrier freq = 2pq so 2 x 1/50 - 1/25 (only use q as it is small)
Offspring risk = prob both parents carriers x risk of affected offspring
2/3 (carrier risk of unaffected sibling of affected) x 1/25 (if no family history, use pop carrier risk) x 1/4 = 2/30 = 1/150

47
Q

What does calc using HWE allow?

A

prenatal diagnosis + cascade testing - testing rel at risk for common genetic disorders esp if pop screening available

48
Q

What is risk of offspring affected by X-linked cond of unaffected parents? (using diagram from lecture)

A

Carrier risk of consultant = 1/2
Risk of passing on gene = 1/2
Prob of having M offspring = 1/2
1/2 x 1/2 x 1/2 = 1/8

GEN (6 decks)

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