basics of gentic disorders - key words Flashcards

1
Q

what is meant by disease anticipation

A

the onset of the disease gets earlier with each generation (and therefore more severe symptoms too)

> Dyskeratosis congeinita - mutation in telomerase components

> huntingdons
fragile x syndrome

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2
Q

what is mutational heterogeneity?

A

mutations in different areas of the gene (promoter, exon, splice site) all lead to the clinically same outcome

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3
Q

what is meant by penetrance

A

the probability of someone with a particular genotype actually expressing the expected/predicted phenotype
does the trait appear in every individual?

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4
Q

what is meant by expressivity

A

refers to the variability/severity of the phenotype seen

in these mouse ear people - large, small, located at top of head or side of head therefore this is variablr expressivity

'’perfect world’’ would have every genotype = 100%/complete penetrance and narrow expressivity

tuberous schlerosis

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5
Q

which best describes mutational heterogeniety
A alleic heterogeniety
B different mutations of the same gene that cause the same disease phenotype
C mutations at different gene loci cause same disease phenotype

A

OPTION B

option c would descibe locus heterogeneity as seen in chondro-dyplasia

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6
Q

can you give an example of variable penetrance?

A

huntingdons AutDOm degenerative disease due to a GOF mutation in HD gene
resulting in a trinucleotide CAG repeat.

repeats longer than 35 in exon 1 can cause disease but a reduced penetracne at 35-39 CAG s
below 35 is not associated with disease onset

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7
Q

can you give an example of mutational heterogeneity

A

duchenne mucsuclar dystophy and beckers MD there is mutation in dystrophin gene so same loci

but a frameshift mutation is more severe than a SP

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8
Q

what is achondroplasia an expamle of?

A

single gene disorder
GOF autosomal dominant mutation in FGFR3
> shows 100% penetrance and narrow expressivity

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9
Q

what is a dominant negative mutations

A

mutatin where the mutant gene loses function and can prevent normal/wild type genes from functioning correctly
> e.g OI where the trimerisation of collagen is interrupted leading to poor fibrilogenesis

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10
Q

can you give an example of variable expressivity

A

marfan syndrome is AUtDom affecting the gene encoding fibrillin
mild - long and thin fingers
severe - defects in blood vessels including aortic aneurysm

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11
Q

what causes non or reduced penetrance?

A

so what does non penetrance mean? we have a mutation but don’t show phenotype
> epigenetic modifications
> x inactivation
> gene interactions
> location of the mutation/ could be on intron

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