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AUDE 5310 Embryology & Genetic Conditions > Chromosomal Disorders (Congenital Monogenetic HL) > Flashcards

Chromosomal Disorders (Congenital Monogenetic HL) Flashcards

1
Q

what is cytogenetics

A

branch of genetics that studies structure and function of the cell, especially chromosomes

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2
Q

what is a characteristic of chromosomal abnormalities?

A

intellectual disabilities
abnormal growth patterns & multiple systems involved

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3
Q

what is aneuploidy

A

numerical aberration of whole chromosome

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4
Q

only ____ autosomal trisomies and ___ sex trisomy can survive

A

3, 1

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5
Q

what are the trisomies that are survivable

A

13, 18, 21, X

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6
Q

why do we think that with advanced maternal age you run the risk of trisomies? (oogenesis)

A

amount of time the egg spends in the diplotene stage
egg doesn’t complete meiosis stage until fertilization
by time is age is older, the egg has been in diplotene stage for this long

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7
Q

what causes an increase in incidence of chromosomal trisomies

A

advanced maternal age

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8
Q

what is trisomy 13

A

Patau syndrome

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9
Q

what are the clinical findings of trisomy 13

A

patau syndrome
brain, heart, difficulty breathing, cleft lip/palate vision problems, extra digits, deformed tectorial membrane - why they dont worry about hearing

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10
Q

rare chromosomal disorder and generally exhibits the most severe birth defects

A

trisomy 13, Patau syndrome

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11
Q

what are the audiological findings in Patau syndrome

A

abnormal helices
low set ear
most show severe to profound bilateral SNHL or deafness

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12
Q

what is trisomy 18

A

edwards syndrome

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13
Q

all trisomies have

A

heart defects, low infertility, intellectual abilities

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14
Q

what are the clinical findings of edwards syndrome

A

profound intellectual disability with seizures
clenched hands with overlapping fingers
high arched palate & small mouth
heart defects

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15
Q

audiologic findings in Edwards syndrome

A

malformed & low set pinnae
most probably severe HL or deaf

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16
Q

___ fetus have higher rates of miscarriage

A

males

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17
Q

what is the most common chromosome defect in humans

A

trisomy 21

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18
Q

what is trisomy 21

A

down syndrome

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19
Q

only ____ of Down’s are born, _____ are fatal

A

30%, 70%

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20
Q

why are people with downs living longer now

A

advancements in medicine, better able to understand what is going on and how to treat them

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21
Q

The incidence of births of children with Down syndrome increases with

A

the age of the mother

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22
Q

what are clinical features in down syndrome

A

flat face (zygomatic bone) and long tongue and short limbs
hypotonia - poor muscle tonew

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23
Q

audiologic findings of trisomy 21

A

low set pinna
stenoic ear canals, middle and inner ear defects
HL can be conductive, mixed, or snhl

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24
Q

what is stenosis

A

small ear canal

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25
Q

HL in 60% of cases with downs is

A

secondary to serious otitis media and impacted cermen in stenoic ear canals

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26
Q

what is microglossia and where is it seen

A

tongue doesn’t fit into the mouth, abnormal smallness of the tongue
down’s

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27
Q

is edwards syndrome mostly male or female

A

female,
males usually higher rates of miscarriage

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28
Q

what percentage is robertsonian translocation in down’s?

A

around 4%

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29
Q

features of robertsonian translocation in seen in

A

acrocentric chromosomes (13, 14, 15, 21, 22)

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30
Q

An acrocentric centromere partitions the chromosome into

A

long arm containing vast majority of genes and short arm with smaller proportion of genetic content

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31
Q

what happens during robertsonian translocation

A

participating chromosomes break at their centromeres and long arms fuse to form single chromosome with single centromere
short arms join together to form another product which contains nonessential genes and is usually lost within a few cell divisions

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32
Q

long arms coming together of the acrocentric chromosomes

A

robertsonian translocation

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33
Q

If RT joins long arm of chromosome 21 with long arm of chromosome 14 (or 15),

A

heterozygous carrier is phenotypically normal or balanced

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34
Q

unbalanced trisomy 21

A

causes down syndrome

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35
Q

balanced trisomy 21

A

normal

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36
Q

RT carrying 14 & 21 + extra chromosome 14 =

A

normal phenotype and heterozygous

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37
Q

Mom Carrier of RT - risk of 2nd trisomy 21 pregnancy =

A

10-15%

38
Q

Dad carrier of RT -

A

risk is <2%

39
Q

An offspring of RT carrier can inherit

A

unbalanced or balanced forms of trisomy 21

40
Q

RT carrying 14 & 21 + extra chromosome 21 =

A

Down Syndrome

41
Q

what is mosaicism

A

two or more cell lines (cell populations) that differ genetically in an individual or tissue but that are derived from a single zygote

42
Q

Mosaicism in single genes can be either

A

somatic or germ cells

43
Q

what does mosaicism explain in rare AD conditions in offspring whose parents are phenotypically normal

A

achondroplasia, hemophilia, some bone diseases

44
Q

sex chromosome mosaicism conditions

A

mosaic klinefelter syndrom
mosaic turner syndrome

45
Q

if the parents are normal how can you have dominant condition?

A

spontaneous condition

46
Q

what is achondroplasia

A

dwarfism

47
Q

what is another name for x inactivation

A

lyonization

48
Q

what is x inactivation

A

form of germ cell mosaicism

49
Q

females inherit ____ as many X chromosomes as males

A

twice

50
Q

what does x inactivation do for females

A

prevents females from having twice as many x chromosome gene products as males
all women are mosaics
we have 2 x chromosomes and men have xy
if both x remained active, we would have too many genes
one x is inactivated (random)

51
Q

once inactivated will it remain inactivated thorughout the lifetime of the cell

A

yes

52
Q

what happens if some of inactivated x genes are still expressing

A

only happens in women which is why autoimmune disorders mostly affect women
these genes create proteins that should not be there

53
Q

is x inactivation variable

A

yes

54
Q

What is a barr body

A

random inactivated x that shows up as a darkened condensed chromosomal region in the cell

55
Q

females are a mix of

A

mix of Xm and Xp

56
Q

what are 3 ways down’s can be inherited

A

trisomy 21 (nondisjunction)
translocation
mosaicism

57
Q

what % is nondisjunction

A

around 95% of cases

58
Q

what % is translocation

A

approx 4% of cases

59
Q

what % is mosaicism

A

around 1% of cases

60
Q

what is nondisjunction trisomy 21

A

prior or at conception, pair of 21 chromosomes in either sperm or egg fails to separate
as embryo develops extra chromosome is replicated in every cell of the body and accounts for an extra chromosome 21

61
Q

what is translocation in trisomy 21

A

part of chromosome 21 breaks off during cell division and attaches to another chromosome (usually chrom 14)
total number of chromosomes in cells remain 46 but presence of an extra part of chromosome 21 causes the phenotype of down syndrome

62
Q

what is mosaicism

A

occrus when nondisjunction of chromosome 21 takes place in one but not all the initial cell divisions after fertilization
when this happens mixture of two types of cells occur with usual 46 chromosomes and others containing 47 (containing the extra 21)

63
Q

individuals with mosaic downs have

A

could have fewer characteristics of downs but it is difficult to broadly generalize due to variability of the condition

64
Q

does mosaicism take place in multiple cells

A

no only one

65
Q

what is a ring chromosome

A

rare genetic condition caused by having an abnormal chromosome that forms a ring
when ring forms both arms break and broken ‘sticky’ ends fuse at the breakage points
broken fragments are lost and any genes that were on them

66
Q

can chromosomes happen on any chromosome

A

yes

67
Q

what are the most common ring chromosomes

A

the acrocentric ones
r13, r14, r15, r21, r22

68
Q

how are majority of ring chromosomes inherited

A

99% from sporadic mutatiosn

69
Q

can ring chromosomes be inherited

A

yes
approx 90% are from mother ring chromosomes associated with reduced fertility in men

70
Q

ring chromosomes have effects on

A

cell growth

71
Q

what can happen to a ring chromosome during cell division

A

may become entangled
broken
double in size

72
Q

what is mosaicism

A

resulting cells that arise with the wrong amount of chromosome material (too much or too little)

73
Q

what is chimerism

A

can manifest as the presence of two sets of DNA or organs that do not match dna of the rest of the organism

74
Q

what is often the result of chimerism

A

two non-identical twin embryos merging together instead of growing on their own

75
Q

what are characteristics of chimerism

A

hermaphroditic, have both males and female sex organs

76
Q

can chimerism have different patches of dna thorughout the body

A

yes

77
Q

what is the karyotype of turner syndrome

A

45 X0

78
Q

which x is absent in 80% of cases

A

paternal x

79
Q

what are the clinical features of turner syndrome

A

short stature and thick/web neck
wide chest and streak gonads
iq slightly below normal

80
Q

what is turner syndrome

A

condition where x linked recessive trait may express phenotypically in females because only one x chromosome is present

81
Q

what is a streak gonad

A

immature gonads
infertile

82
Q

what are the audiologic findings of turner syndrome

A

low set protruding pinna and narrow ear canals
recurrent ear infections and chronic otitis media

83
Q

long term consequences of ear infections?

A

speech and language development delays

84
Q

how do babies learn language

A

incidental learni g

85
Q

x linked recessive - will a female show phenotype of turner syndrom?

A

no because the other x will balance itout

86
Q

what is the phenotype of turner syndrome

A

they look like females

87
Q

what is the single most common cause of male infertility?

A

klinefelter’s syndrome

88
Q

what is klinefelter’s syndrome

A

47, xxy
they have two XX and a Y

extra sex chromosome

phenotype is a male because of the Y

89
Q

47 xxy

A

klinefelter syndrome

90
Q

what are the clinical features

A

tall and thin with disproportionately long legs
development normal until puberty
poor attention and judgment
behavior and psychosocial problem

91
Q

what are the audiological features of Klinefelter’s syndrome

A

SNHL in cases reported with poor auditory discrimination and delayed speech development

AUDE 5310 Embryology & Genetic Conditions (18 decks)

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