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MCD Genetics > 1 Mrs. Jones's First Consultation > Flashcards

1 Mrs. Jones's First Consultation Flashcards

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1
Q

Q: What ratio of newborns are born with congenital abnormalities? What percentage of congenital abnormalities are caused by genetic factors?

A

A: 1:50

40

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2
Q

*Q: List the 7 classifications of congenital abnormalities (birth defects). Place in 2 categories.

A

A: Single:

Malformation
Disruption
Deformation
Dysplasia

Multiple:

Sequence
Syndrome
Association

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3
Q

*Q: Describe malformation as a congenital abnormality. Defect type? Examples? (3) Result of? Part of body?

A

A: morphological defect // primary structural defect

eg congenital heart defects, atrial septal defects, cleft lip

resulting from an intrinsically abnormal developmental process

Usually involves single organ showing multi-factorial inheritance.

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4
Q

Q: What is multi-factorial Inheritance? (2)

A

A: many factors are involved in causing the birth defect. Factors are both genetic and environmental.

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5
Q

*Q: Describe disruption as a congenital abnormality. Defect type? Example? Result of? Caused by? 3 step pathway?

A

A: morphological defect // Secondary abnormal structure

e.g. amniotic band causing digital amputation (when the amniotic band wraps around a digit, restricting the blood flow and leading to amputation)

resulting from extrinsic breakdown of/or interference with an originally normal development process.
Caused by ischaemia, infection and trauma. It is NOT genetic but genetic factors can predispose

starts as normal -> something occurs part way (early on) -> something is often not fully formed

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6
Q

*Q: Describe deformation as a congenital abnormality. Deformation type? Examples? (2) Result of? Normalised? Why?

A

A: physical deformation

e.g. club foot, hip dislocation

abnormal form, shape or position of a part of the body caused by mechanical forces

can be normalised (key difference) -> corrective footwear, surgery, physiotherapy because it occurs late in pregnancy
good prognosis because the underlying structure is normal (develops normally first)

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7
Q

*Q: Describe dysplasia as a congenital abnormality. What is it? Example?

A

A: Abnormal organisation of cells into tissue and its morphological result

e.g. thanatophoric dysplasia

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8
Q

Q: What is thanatophoric dysplasia? Caused by? High recurrence risk where? Features?

A

A: type of dysplasia which is a congenital abnormality

Caused by a single gene defect (FGFR3)

High recurrence risk for siblings/offspring

Bowed long bones, narrow thorax, large skull

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9
Q

*Q: Describe sequence as a congenital abnormality. Example?

A

A: pattern of multiple anomalies derived from a single known or presumed prior anomaly or mechanical force

eg potter sequence

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10
Q

Q: What is the ‘potter sequence’? Caused by? 3 step sequence? What could the initial factor be? Features (3).

A

A: congenital abnormality

Caused by Oligohydramnios -

urogenital abnormality eg blocked urethra -> reduced urine output -> Oligohydramnios (reduced volume of amniotic fluid due to failure to produce urine)

Could have a genetic component as the initial factor

potter facies, pulmonary hypoplasia (lungs don’t develop properly), clubbed feet

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11
Q

*Q: Describe syndrome as a congenital abnormality. What is it? (2) Example? Includes?

A

A: multiple anomalies thought to be pathogenetically related and not representing a sequence

Consistent pattern of abnormalities with a specific underlying cause

e.g. Down Syndrome

This includes chromosomal abnormalities

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12
Q

*Q: What is down syndrome also known as? Mental feature? Craniofacial features? (5) Oral features? (3) Limb features? (3) Heart? Muscle tone? Height?

A

A: trisomy 21

mental retardation

broad flat face
short nose
epicanthic eye fold
small ears
brushfield spots (pale spots around iris)

small and arched palate
big wrinkled tongue
dental abnormalities

palm crease
short and broad hands
toes widely spread

congenital heart disease

diminished muscle tone

short

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13
Q

*Q: Describe association as a congenital abnormality. Example? Cause?

A

A: non random occurrence in 2 or more individuals of multiple congenital abnormalities not known to be a polytopic defect, sequence, or syndrome

(Non-random occurrence of abnormalities NOT explained by syndrome)

eg VACTERL assocation

Cause is typically unknown

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14
Q

Q: Describe VACTERL association.

A 
A: Vertebral anomolies
Anal atresia
Cardiac defects
Tracheo-Oesophagal fistula
Renal/radial anomolies
Limb defects
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15
Q

Q: List the levels of genetic organisation (5).

A 
A: base pairs
DNA
gene (code for proteins)
chromosome (genes packed together)
genome (total)
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16
Q

Q: How many chromosomes do we inherit from our parents? Type? Number? Total?

A

A: from each parent we inherit:
22 autosomes
1 sex chromosome (X or Y)

haploid number

diploid number= 46

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17
Q

Q: Describe the structure of chromosomes. 3 types?

A

A: Chromosomes have a short arm and a long arm. They are sometimes referred to as the P (petite) arm and the Q arm.

each chromosome has 2 arms that are joined at the centromere

Telomere are the longer arms
Chromatids are the shorter arms (can be replaced by satellites)

Type of chromosomes depends on the location of the centromere:

Centromere in the middle = Metacentric

Centre more towards one side = Submetacentric

Don’t have short arms (Satellites) = Acrocentric

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18
Q

*Q: Describe the human karyotype. Visualised by?

A

A: the chromosome set of an individual or species described in terms of both the number and structure of the chromosomes. The representation of the chromosomes set in a diagram.

The human karyotype is visualised by staining with Giemsa (fluorescent dye) and are numbered essentially by size

19
Q

*Q: How are parts of chromosomes identified? Example.

A

A: Chromosome Banding: There is a standard human banding pattern due to the staining which is the same for everyone. The centromere is the start point. You number out from the centromere starting from 11.

It can be written in short hand in the following sequence:

  1. Chromosome number
  2. P or Q arm
  3. Band number

NOTE: Different stains will give different numbers of bands.

CFTR 7q31.2 (7th chromosome, long arm, band 31.2)

20
Q

Q: What are the 3 types of chromosome abnormalities?

A

A: structural
numerical
mosaicism

21
Q

Q: How are structural chromosome abnormalities seen? Examples? (5)

A

A: under a microscope

translocations, deletions, insertions, inversions, rings (ends join together)

22
Q

*Q: What are numerical chromosome abnormalities?

A

A: aneuploidy, loss or gain of chromosomes (abnormal number of chromosome)

23
Q

Q: Describe mosaicism as a chromosome abnormalities. Expression? Example? What determines how many cells are affected?

A

A: different cell lineages do not contain identical chromosomes - a condition in which the cells of an individual do not all contain identical chromosomes; there may be two or more genetically different populations of cells.

In affected individuals the chromosome defect is usually not fully expressed.’

eg if trisomy 21 developed part way -> some cells are affected only

How early the mitotic non-disjunction happens will determine how many tissues and which tissues the genetic abnormality might affect.

24
Q

Q: What is a translocation?

A

A: exchange of genetic material between 2 chromosomes

25
Q

*Q: 3 ways to describe chromosomes that have (not got) translocations.

A

A: There could be translocations (structural abnormalities) of certain parts of the chromosomes.

NORMAL - when no translocation takes place

BALANCED - when there is a straight switch of the sections of DNA - no genetic material lost

UNBALANCED - when part of the chromosome is lost - GENETIC MATERIAL IS LOST - if an important gene is lost, it could result in a non-viable embryo

26
Q

*Q: What can happen when someone has a balanced translocation? Diagram.

A

A: When someone with a balanced translocation is undergoing meiosis, their chromosomes will form a quadravalent whereas it would normally be a bivalent.

When this happens you can get some strange exchanges of genetic material and odd outcomes which can cause disease (phenotype eg leukaemia)

REFER

27
Q

Q: What is a derivative? Abbreviated?

A

A: chromosome which looks like it has had a translocation. Abbreviated to der.

28
Q

*Q: What are the 4 ways to describe aneupleudy

A

A: monosomy- loss of a single chromosome (always lethal)

disomy- normal

trisomy- gain of 1 chromosome (can be tolerated for specific chromosomes)

tetrasomy- gain of 2 chromosomes (can be tolerated for specific chromosomes)

29
Q

*Q: What are the 3 chromosomes that are viable in trisomy form?

A

A: 13, 18, 21

Trisomy 13 - Patau Syndrome

Trisomy 18 - Edwards Syndrome

Trisomy 21 - Down Syndrome

30
Q

*Q: List Patau syndrome’s 3 features.

A

A: (trisomy 13)

  • Heart Defects (septal, patent ductus arteriosus)
  • Holoprosencephaly (cleft lip/palate, hypotelorism)
  • Mental Retardation
31
Q

*Q: List Edwards syndrome’s 4 features.

A

A: (trisomy 18)

  • Heart Defects (septal, patent ductus arteriosus)
  • Kidney Malformation (horseshoe kidney)
  • Digestive Tract Defects (omphalocele, oesophageal atresia)
  • Mental Retardation
32
Q

*Q: What are the 3 newborn features of down syndrome?

A

A: excess nuchal skin
lethargy
hypotonia- floppy/limp

33
Q

*Q: What explains down syndromes association with maternal age?

A

A: 90% maternal origin of extra chromosome

34
Q

*Q: What are 95% of all Down Syndrome cases caused by?

A

A: non-disjunction during meiosis I (75%) and meiosis II (25%)

NON-DISJUNCTION = FAILURE TO SEPARATE

35
Q

*Q: What are 4% of all Down cases caused by? Special case? 2/3? 1/3?

A

A: TRANSLOCATIONS

ROBERTSONIAN TRANSLOCATION

2/3 de novo translocations in child - has happened during meiosis or in early mitosis (embryo genesis stage)- no evidence of inheritance - parents don’t have it at all.

1/3 of parents are carriers of translocation - have high risk of further downs.

36
Q

*Q: Describe the robertsonian translocation?

A

A: Breakage at the centromere of the 2 chromosomes 21 which are acrocentric. -> fusion of their long arms to form one new derivative chromosome -> get chromosome which has additional genetic material

results in down syndrome

37
Q

*Q: What is mosaicism caused by? What can it affect? what percentage of cases? Effect on children? What determines severity?

A

A: mitotic non-disjunction

has an effect on Down Syndrome - 1% of cases

Children are less severely affected because the non-disjunction has occurred during mitosis

The type of cells and the time at which the non-disjunction occurred will determine severity (if v late may not even be clinically noticeable)

38
Q

*Q: Turner’s syndrome. Caused by? Phenotypical sex? 2 prenatal features? 2 features? Intelligence? Height? Fertility? Treatment?

A

A: monosomy X

80% due to loss of X or Y chromosome in paternal meiosis
20% other causes (ring chromosome, single arm deletion, mosaicism)

female

Generalised oedema and swelling in neck region can be detected in 2nd trimester.

webbed neck, aorta defect in 15% of cases

Normal Intelligence

In adults: short statue (without GH treatment), ovarian failure (infertility)

Treatment - oestrogen replacement for secondary sexual characteristics and prevention of osteoporosis.

39
Q

*Q: Kleinfelter’s Syndrome. Cause? Rare variations? (2) Phenotypical sex? 3 physical features? 2 characteristics? Fertility? Increased risk? (3)

A

A: 47, XXY

X chromosome from either mother or father

48, XXXY and 49, XXXXY are very rare

male

Taller than average, long lower limbs, 30% - moderately severe gynaecomastia (enlargement of man’s breasts)

Clumsiness, verbal learning disability

All infertile

Increased risk of leg ulcers, osteoporosis and breast carcinoma in adult life

40
Q

*Q: What dosage compensation ensure? 3 mechanisms?

A

A: equivalent gene expression in both sexes (explains why men are fine with 1 X chromosome while women suffer Turners)

  1. random inactivation of a single X chromosome in females (most mammals)- lyonization, formation of Barr bodies) -> see a clump of genetic material at edge which is basically the X chromosome)
  2. increased (x2) expression of X chromosome genes in males
  3. decreased expression of both X chromosome genes in hermaphrodites
41
Q

*Q: How can you be chromosomally one gender and phenotypically the other gender?

A

A: because of translocation.

The Y chromosome has a SEX DETERMINING REGION ON THE Y (SRY) - this is what makes males male- codes for a transcription factor which causes gonads to develop as testes and degeneration of female ducts

If there is a translocation of the SRY from the Y to the X you can get an X chromosome with a male determining factor and a Y which has LOST the male determining factor so phenotypically the XX will be male and the XY will be female.

42
Q

*Q: What are genomic disorders caused by? 2 types? Karyotype?

A

A: loss/gain of DNA

  1. Deletion Syndrome - e.g. Di George Syndrome
  2. Duplication Syndrome - e.g. Charcot-Marie-Tooth disease type 1A

These may not be visible in the karyotype because they are micro-deletion syndromes

43
Q

*Q: Di George Syndrome. Is? Diagnostic features? (5)

A

A: Micro-deletion of 22q11.2 region containing the gene TBX1

Diagnostic Features:

-Cardiac abnormalities (e.g. tetralogy of Fallot)
-abnormal facies (low set ears, widely spaced eyes)
-Hypoplastic Thymus
-Hypocalcaemia (parathyroid hypoplasia)
-cleft palate
22

44
Q

Q: Charcot-Marie-Tooth disease type 1A. Is? Diagnostic features? (6) Adolescence? Treatment (2).

A

A: Micro-duplication of PMP22 gene on Chr 17

Diagnostic Features:

  • Foot drop
  • Distal muscle wasting/weakness
  • Foot deformities - high arches or flat feet
  • Absent reflexes
  • Lack of sensation in upper/lower limbs
  • Slow nerve conduction velocity

demyelinating peripheral neuropathy in adolescence

physiotherapy, corrective surgery

MCD Genetics (7 decks)

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