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PATHO > Lecture 8 + 9: Genetic Diseases > Flashcards

Lecture 8 + 9: Genetic Diseases Flashcards

1
Q

single gene, mendelian traits

A

-inheritance patterns
-penetrance and expressivity
-sources mutations
-effects of mutations on gene function
-how do variants lead to dominant and recessive traits?

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2
Q

cytogenetic disorders

A

-down syndrome

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3
Q

single gene disorders with atypical patterns of inheritance are diseases caused by:

A

-triplet repeat mutations
-mutations in mitochondrial genes
-genomic imprinting

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4
Q

Inheritance patterns of single gene disorders

A

-recessive
-dominant
-autosomal
-sex-linked

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5
Q

autosomal

A

involves chromosomes 1-22

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6
Q

Autosomal recessive trait inheritance

A

-25% noncarrier
-50% carriers
-25% affected

-all children of an affected parent are carriers
-early sge of onset usually
-more uniform symptoms compared to dominant disorders

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7
Q

Inheritance of autosomal dominant trait

A

-50-50 chance of passing trait to child
-NO carriers
-delayed age of onset
-huntington diseases signs appear later in life

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8
Q

Penetrance

A

-% of ppl who have certain mutation show traits associated with defects in the gene
-complete=100%
-incomplete<100%

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9
Q

Expressivity

A

-mutations giving rise to different outcomes in different ppl
-different number, identity, extent (severity)
-range from complete to minimal

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10
Q

Expressitivity is affected by:

A

-other genes
-Exposure to harmful chemicals or
conditions
-Environment
=Age

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11
Q

Types of variants

A

-benign
-likely benign
-pathogenic
-likely pathogenic
-uncertain significance

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12
Q

How do variants occur

A

-inherited
-non-inherited
-new de novo variants

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13
Q

Iherited variants

A

-from parent to child
-in almost every cell of body thru life
- germline variants present in the parent’s germ cells

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14
Q

Non-inherited variants

A

-occur at some time during life
-not every cell
-somatic variants
-not passed down
-can be caused by environment

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15
Q

New de novo variants

A

-found in child but neither parent
-may occur in egg but not be present in other cells or in egg after uniting with sperm
-variants aquired during development can lead to mosaicism

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16
Q

Types of genetic variants

A

-substitutiions (silent, missense, nonsense)
-frameshift (insertion, deletion)

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17
Q

silent mutations

A

-redundant amino acids
-no effect on protein function

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18
Q

missense mutation

A

-wrong nucleotide
-leads to wrong amino acid which will ruin protein

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19
Q

nonsense mutation

A

-wrong nucleotide
-leads to STOP sequence
-terminates protein early

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20
Q

Frameshift mutations (insertions and deletions)

A

-lead to incorrect amino acid sequence down the line

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21
Q

Can pathogenic variants occur in areas other than protein coding sequences?

A
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22
Q

amorphic

A

loss of function

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23
Q

hypomorphic

A

partial loss of function

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24
Q

hypermorphic

A

gain of function

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25
dominant negative
-inhibits activity of unmutated protein
26
neomorphic
aquisition of new property
27
Cystic Fibrosis (autosomal RECESSIVE)
-most common lethal disease of white people -loss of function mutations in CFTR
28
CFTR variants have different effects on CFTR
-ppl fare better with variants with PARTIAL activity instead of complete loss of function -variants establish dose-response relationship -mild CF when CFTR alleles have 10-20% function
29
Ivacaftor
-increases function of CFTR protein -works only on specific genotype -improves clinical symptoms
30
How does loss of function lead to recessive effect?
-most times, the unmutated copy of the gene is not able to make up for the loss of expression or activity from the mutate gene -no dosage compensation
31
What level of expression is required for full activity?
slide 25
32
How does loss of function lead to dominanr effect?
-osteogenesis imperfecta -point mutations -gain of function
33
Osteogenesis imperfecta
-defects in collagen production -most abundant protein in body -collagen trimer -loss of proa1 -dominant negative effect caused by point mutations
34
collagen trimer
-2 subunits of a1 -1 subunit of a2
35
Autosomal dominant caused by gain of function
-LDL receptor levels regulated by PCSK9 which
36
PCSK9
-binds LDL on cell surface -internalized with LDLR -direct LDLR to lysosome -LDLR completely degraded -reduces number of LDLRs on cell
37
PCSK9 gain of function effect:
-increase affinity for LDL-R -enhance sorting of LDL-R to lysosome
38
Autosomal dominant caused by loss of function
-familial hypercholesterolemia (FH) -most often caused by mutations in the LDLR ->3000 pathogenic variants
39
Inheritance of X-linked recessive
-50% chance of passing gene -only males are affected -affected males pass gene to daughter but not to sons -female can be affected if father has trait and mother is a carrier (rare)
40
X-linked genetic diseases
-hemophilia A and B: -joint bleeding, muscle hematoma, soft tissue bleeding
41
hemophilia A
-factor VIII -inversion and small deletion mutations
42
hemophilia B
-factor IX -missense mutations -more common
43
Disease caused by triplet repeat mutations
-Fragile X syndrome -some genes contain repeats of 3 nucleotides -longer repeats disrupt gene function -~40 diseasees all associated with neurodegradations
44
Fragile X syndrome
-mental retardation -FRM1 gene on X chromosome gets silenced -expanded CGG sequence -methylation
45
Diseases Caused by mutations in mitochondrial genes are RARE
-mutations in mitochondrial genes are transmitted to progeny by DAUGHTERS, but not sons -affect organs that depend most on oxidative phosphorylation (muscle, heart, brain)
46
mitochondria
-separate genome -multiple copies per cell -are inherited only from MOTHER
47
Cytogenetic disorders
-chromosonal abnormalities -frequent -change in chromosome number or structure -can affevt autosomes or sex chromosomes -disorders characterized by a change in autosome number are more severe (more genes involved) than single gene disorders
48
Common chromosomal abnormalities
-translocation -isochromosome -deletion -inversions -ring chromosome
49
translocation
-transfer of part of one chromosome to another chromosome
50
isochromosome
-centromere divides horizontally rather than vertically -results in 2 short arms and 2 long arms only
51
Deletion (chromosome)
-loss of a portion of a chromosome
52
Inversions (chromosome)
-2 intersitial breaks -segment reunites but is flipped
53
Ring chromosome
-variant of deletion -after loss of segments from each end, arms unite to make a ring
54
Karotype
chromosome map
55
Chromosome nondisjunction
??slide 40
56
Genetic diseases with abnormal chromosome numbers
-down syndrome (trisomy 21) -turner syndrome (monosomy X)
57
genetic imprinting
-parent of origin transmission -some reegions of DNA inactivated (silenced) in copy received from mother or father -maternal/paternal -occurs in ovum or sperm -transmitted to all somatic cells from zygote -if a gene that is turned off in the maternal copy is mutated in the paternal copy, genes in that region will not be expressed -complex inheritance patterns
58
Diseases involving genomic imprinting
-Prader-Willi syndrome -Angelman syndrome
59
angelman syndrome (from mother)
-region of chromosome 15 deleted -from mother -mental retardation -ataxic gait -seizures -inappropriate laghter
60
Prader-Willi syndrome
-deletion of region of chromosome 15 -from father -mental retardation -short stature -hypotonia -obesity -small hands and feet -hypogonadism

PATHO (31 decks)

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