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2nd year > Missing X chromosomes and triple repeat disorders > Flashcards

Missing X chromosomes and triple repeat disorders Flashcards

1
Q

what regulates sex determination?

A

gene on short arm of Y chromosome - SRY gene

without it all embryos would develop as female

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2
Q

what regulates sex determination?

A

gene on short arm of Y chromosome - SRY gene

without it all embryos would develop as female

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3
Q

SRY gene expression

A

at 7 weeks gestation

causes production of androgens leading to development of male embryo

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4
Q

what is karyotype?

A

an individuals collection of chromosomes

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5
Q

XX male karyotype

A

SRY gene has been translocated onto the X chromosome by crossing over
causing a male embryo to develop but with 2 X chromosomes

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6
Q

clinical features of XX male

A

small testes
sterile
ambiguous internal and external genitalia
male phenotypes

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7
Q

SRY mutation

A

XY genotype with female phenotype

due to inactivation of SRY gene

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8
Q

pseudoautosomal regions on X and Y chromosomes

A

2 regions
PAR 1 and 2 on X and Y chromosomes
help the 2 chromosomes align in meiosis and pair to allow recombination

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9
Q

X chromosome aneuploidies affecting males

A

klinefelter syndrome
XYY syndrome
Y chromosome rearrangements

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10
Q

X chromosome aneuploidies affecting females

A

Turner syndrome

Trisomy X syndrome

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11
Q

Klinefelter syndrome karyotype

A

XXY

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12
Q

clinical features of Klinefelter syndrome

A 
taller and thinner than average
poor beard growth 
gynaecomastia
infertile 
defective spermatogenesis
small testes
reduced testosterone production 
reduced IQ
mostly lead a normal life
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13
Q

epidemiology of Klinefelter syndrome

A

common - 1/1000
extremely rare forms = XXXY or XXXXY
common live birth
50% miscarriage risk

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14
Q

Karyotype for XYY syndrome

A

XYY

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15
Q

Karyotype for Y chromosome rearrangements

A

X del (Yq)

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16
Q

Karyotype for Turner Syndrome

A 
X
Xdel(Xp)
Xi(Xq)
X mar 
missing X chromosome
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17
Q

Karyotype for Trisomy X syndrome

A

XXX

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18
Q

clinical features of Turner Syndrome

A 
short
no puberty
webbed neck
underdeveloped breasts
infertile
broad chest
widely spaced nipples
low IQ
normal life expectancy 
presents in mosaic form
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19
Q

epidemiology of Turner syndrome

A

1/2500

spontaneous abortion is high

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20
Q

what is mosaicism?

A

different cells in the body have different chromosome composition
this rescues missing X chromosome phenotype
the cells replicate the single X chromosome in some cells then form a normal line of cells

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21
Q

SRY gene expression

A

at 7 weeks gestation

causes production of androgens leading to development of male embryo

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what is karyotype?

A

an individuals collection of chromosomes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

XX male karyotype

A

SRY gene has been translocated onto the X chromosome by crossing over
causing a male embryo to develop but with 2 X chromosomes

24
Q

clinical features of XX male

A

small testes
sterile
ambiguous internal and external genitalia
male phenotypes

25
Q

SRY mutation

A

XY genotype with female phenotype

due to inactivation of SRY gene

26
Q

pseudoautosomal regions on X and Y chromosomes

A

2 regions
PAR 1 and 2 on X and Y chromosomes
help the 2 chromosomes align in meiosis and pair to allow recombination

27
Q

X chromosome aneuploidies affecting males

A

klinefelter syndrome
XYY syndrome
Y chromosome rearrangements

28
Q

X chromosome aneuploidies affecting females

A

Turner syndrome

Trisomy X syndrome

29
Q

Klinefelter syndrome karyotype

30
Q

clinical features of Klinefelter syndrome

A 
taller and thinner than average
poor beard growth 
gynaecomastia
infertile 
defective spermatogenesis
small testes
reduced testosterone production 
reduced IQ
mostly lead a normal life
31
Q

epidemiology of Klinefelter syndrome

A

common - 1/1000
extremely rare forms = XXXY or XXXXY
common live birth
50% miscarriage risk

32
Q

Karyotype for XYY syndrome

33
Q

Karyotype for Y chromosome rearrangements

A

X del (Yq)

34
Q

Karyotype for Turner Syndrome

A 
X
Xdel(Xp)
Xi(Xq)
X mar 
missing X chromosome
35
Q

Karyotype for Trisomy X syndrome

36
Q

clinical features of Turner Syndrome

A 
short
no puberty
webbed neck
underdeveloped breasts
infertile
broad chest
widely spaced nipples
low IQ
normal life expectancy 
presents in mosaic form
37
Q

epidemiology of Turner syndrome

A

1/2500

spontaneous abortion is high

38
Q

what is mosaicism?

A

different cells in the body have different chromosome composition
this rescues missing X chromosome phenotype
the cells replicate the single X chromosome in some cells then form a normal line of cells

39
Q

what is X inactivation?

A

most of the genes on the second X chromosome become inactivated in females = dosage compensation

40
Q

what is dosage compensation?

A

random process occurring early in embryogenesis, occurs by coating the X chromosome with RNA molecule so it becomes condensed and cannot produce any protein

41
Q

x chromosome vs Y chromosome

A

X contains 800 genes, but Y is gene poor

42
Q

what causes X inactivation?

43
Q

x-linked diseases

A

no male to male transmission
predominantly affects males, as females protected by second normal X chromosome
dominant conditions can affect females

44
Q

examples of x-linked diseases

A

Haemophilia A and B

Duchenne muscular dystrophy

45
Q

x-linked dominant inheritance

A

no male-to-male transmission
females can be more often affected than males
females less severely affected

46
Q

examples of x-linked dominant inherited conditions

A

Rett syndrome

fragile X syndrome

47
Q

Rett syndrome

A 
delayed development from 1 year
autism
absent speech
lose ability to walk
de novo mutation
predominantly affects girls because it is lethal in males
48
Q

Fragile X syndrome

A 
causes developmental delay 
diagnosed early in childhood
attention deficit 
autism
seizures
females less severely affected
trinucleotide repeat disorder
49
Q

fragile X syndrome

A

trinucleotide repeat in FMR1 gene
CGG repeats cause methylation of CGG and inactivates the FMR 1 gene
looks like broken X chromosome under microscope

50
Q

number of CGG repeats

A

<55 healthy - 30 most common

fragile X syndrome = >200 repeats

51
Q

FMR 1 gene

A

on end of long arm of x chromosome

52
Q

what are trinucleotide repeat disorders?

A

unstable expansion during meiosis
number of repeats increases with reproduction
can be mediated by DNA, RNA or protein

53
Q

features of trinucleotide repeat disorders

A

some affect coding region

show anticipation

54
Q

CAG repeats

A

polyglutamine in proteins

55
Q

disorders caused by trinucleotide repeats

A

myotonic dystrophy
huntington’s
>30 disorders

56
Q

what is anticipation?

A

increased clinical severity or younger age of onset in successive generations of disease - fragile X is an exception to this

57
Q

myotonic dystrophy

A

symptoms more severe and occur earlier further down the generations

2nd year (48 decks)

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