Molecular basis of neurological disorders Flashcards

1
Q

describe layout of a gene

A

5 prime untranslated region
transcribed into mrna but not translated
-start site for translation to occur

coding section of gene– exon, interrupted by introns (not in final message as removed by splicing)

stop codon followed by
3 prime untranslated region

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2
Q

what is a trinucleotide
and why do neurological diseases occur here

A

3 nucleotides repeated consecutively many times
repeated in any section of the gene

repetition in a number of sequences result in a disease
-eg. number of repeats increased

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3
Q

what is huntintons disease
symptoms
which part of brain affected

A

autosomal dominant
present midlife
involuntary
chorea
dystonia
behavioural changes
psych changes
gradual loss of cognition and death

striatum
atrophy of caudate nucleus and putamen

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4
Q

what is the genetic basis behind huntingtons

A

expansion of a trinucleotide repeat
CAG (which codes for GLUTAMINE)
–POLYGLUTAMINE in exon therefore protein is altered

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5
Q

why is extra glutamine harmful?

A

Huntingtin protein misfolds
aggregates
inclusion bodies

in protein:
beta pleated sheet with hydrogen bonds from one side of sheet to the other

R group lined up with R group on other strand of beta sheet
if both are glutamine- potential for additional hydrogen bonding– giving structure more stability which forms AGGREGATES

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6
Q

what is fragile x syndrome
symptoms

A

leading cause of inherited mental impairment
SINGLE GENE DISORDER on the X chromosome
affects men and women
-more severe for men as only one X chromosome

long face with prominent forehead and jaw
mitral valve prolapse
mental impairment
attention deficit
autistic like behaviour-tactile defensive, poor eye contact, HAND FLAPPING

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7
Q

What is the genetic basis behind fragile x syndrome

what is the role of the FMR1 PROTEIN

A

FRM1 gene (fragile x mental retardation)
trinucleotide CGG repeated in the 5’ untranslated region of gene

FMR1 protein is highly expressed in neurons

gene regulates BY REPRESSING mRNA translation so dont get xs protein

The FMR1 gene provides instructions for making a protein called FMRP. this protein regulates the production of other proteins by stopping the translation of other mRNA, by dampening down response to glutamate

in absence of FMRP (in fragile X) mRNA translation occurs in abundance, as xs glutamate signalling– get xs mRNA translation– lots of protein– FRAGILE X SYNDROME

The abnormally expanded CGG segment turns off (silences) the FMR1 gene, which prevents the gene from producing FMRP. Loss or a shortage (deficiency) of this protein disrupts nervous system functions and leads to the signs and symptoms of fragile X syndrome

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8
Q

What are some ways to potentially prevent loss of fragile x protein

A

block glutamate signalling
with GLUTAMTE ANTAGONIST
therefore block signalling

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9
Q

why are trinucleotides susceptible to expansion

A

unwound can form a HAIRPIN structure and form double helix on its own

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10
Q

what is genetic anticipation and give an example of a disease

A

signs and symptoms of a disease become more severe down generations, and appear at an earlier stage

myotonic dystrophy
-progressive muscle wasting and weakness

more expansion

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11
Q

why does genetic anticipation help clinically

A

Msh3 gene
dna mismatch repair gene
more copies=increase expansion

create an inhibitor to prevent expansion?
but it is important in other protection like colon cancer

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12
Q

What is an experimental treatment for huntingtin being done right now

A

antisense oligonucleotides
to block expression of protein that is causing problem

huntingtin gene and oligo causes hybridisation
this is then targeted for DEGRADATION and cant make protein if no mrna
reduced production of HTT

can use different antisense oligonucleotides for different diseases

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13
Q

what is interesting about early onset AD

A

early onset
inherited autosomally dominant
5% of all AD
also if have downs syndrome it is a high risk

gene present on chromosome 21? putting you at risk of AD

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14
Q

what protein is present on chromosome 21 (AD)
why is this an issue

A

AMYLOID PRECURSOR PROTEIN
more protein = more at risk of AD

protein concentrated in neurons regulating synapse formation

cleaved by different enzymes

normal:
cleaved by alpha secretase

sometimes:
also cleaved by beta and gamma secretase
forming amyloid beta peptide== aggregate outside the cell forming deposits

AD (familial):
in some families there are mutations in the APP to increase beta secretase cleavage

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15
Q

what gene mutations are associated with early onset familial AD

A

presenilin 1 (70%)
presenelin 2 (5%)
subunits of gamma secretase

APP (10-15%)

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16
Q

what are some genetic risk factors for SPORADIC AD

A

APOE gene
-3 alleles which differ by one amino acid
-eta2, 3, 4

heterozygotes for E4 3 fold risk
homozygotes for E4 15 fold risk

17
Q

what does ApoE do (sporadic AD)

A

involved in Cholesterol transport
clears amyloid beta

variant eta4 not good at cholesterol transport
therefore more cholesterol in lipid membrane,
more cholesterol favours cleavage by gamma secretase route– more amyloid beta

eta4 not clearing amyloid beta

eta4 broken down creates toxic products

18
Q

what is a genome wide association study

A

patients vs non-patients
mix DNA together
compare differences to discover SNPs associated with disease
–manhatten plot

19
Q

what are some other genes (not ApoE) involved in sporadic AD

A

clusterin- bind amyloid beta (clearance)
PICALM- endocytosis of amyloid beta

therefore if variation- problem with removal

there are lots of gene!
-minor variations in lots of genes– add little risk
therefore can add up to give a HIGH RISK

20
Q

how are neurofibrillar tangles related to plaques

A

TAU stabalises microtubules

if tau is phosphorylated microtubules are depolymerised
–paired helical fragments

frontotemporal dementia has tau but no plaques
–maybe tau is the only bad thing in brain?

21
Q

how does genetic info help therapeutically?

A

aggregation inhibitors?
secretase inhibitors (gamma)?
prevent phosphorylation of tau?
statins?
immunisation?

22
Q

what are some prion diseases

A

creutzfeld-jokob disease
fatal familial insomnia
kuru

23
Q

what are prion diseases

A

transmissible spongiform encephalopathy

10-15% inherited
85% sporadic
acquired normally rare

24
Q

what is spongiform

A

scarring
prion deposition
porous structure

25
Q

what is prion

A

only protein
infectious agent
no genetic material

v resistant to heat and disinfectant
-unique conformation that changes and allows it to alter conformation of other proteins

this can spread from neuron to neuron
-deposition of amyloid like fibres, kills neurons, astrocytes invade to remove dead neurons leaving behind spongiforms.

PRPN prion precursor protein
-gpi anchor
-glycosylated
-synaptic membranes of neurons

26
Q

discuss variant CJD

A

copared to sporadic–
pre-clinical transmission concerns
as long incubation period
therefore, scrutinise blood giving

polymorphism M129V can determine susceptibility to vCJD (patients MM genotype)

prospects for therapy:
stabalising PrPc conformation
clearance of PrPsc

vaccination against PrPsc