Huntington's

Question 1

What year was the HTT gene discovered and by who

Answer 1

1993, MacDonald et al

Question 2

What does HTT gene encode

Answer 2

HTT protein

Question 3

What is CAG repeat code for

Answer 3

Glutamine repeat

Question 4

What expansion becomes pathological (number)

Answer 4

> 36

Question 5

Anticipation

Answer 5

Severity increases and age of onset decreases with subsequent generations

Question 6

HTT’s exact function is not known, but its interactions with many proteins have been identified

Answer 6

Harges and Wanker, 2003, Li et al., 2004

Question 7

HTT knockout mice do not survive development, however mice homozygous for mutant HTT survive this phase

Answer 7

Dragatsis et al., 2000, Leavitt, 2011

Question 8

Which pathway degenerates first

Answer 8

indirect

Question 9

Which striatal neurons degenerate first

Answer 9

Those projecting to the GPe

Question 10

Later affected pathway

Answer 10

Direct

Question 11

Transgenic mice expressing expanded CAG tracts display widespread intracellular inclusions

Answer 11

Davies et al., 1999

Question 12

However, the presence of inclusions does not correlate with neuronal cell death in fact it has been shown to be protective

Answer 12

Arrasate et al., 2004

Question 13

Current therapeutics

Answer 13

Tetrabenazine

Question 14

Tetrabenazine MoA

Answer 14

Binds to and inhibits VMAT (inhibits DA from being put in vesicles) and binds to postsynaptic DARs inhibiting DA action

Question 15

Factors to consider in gene silencing

Answer 15

1. Delivery 2. Immunoreaction 3. Targets - length of repeats (where do you stop), SNPs (there are many) 4. Allele specific?

Question 16

How was gene silencing delivered in IONIS-HTTrx trial

Answer 16

Intrathecally

Question 17

Who came with brain shuttle tech allowing therapeutics to bind to naturally occurring receptors and cross the BBB?

Answer 17

Roche

Question 18

Gene silencing is by antisense oligonucleotides or interfering RNA - both short nucleic acid sequences whic block transcription of target protein, preventing expression

Answer 18

Godinho et al., 2015

Question 19

In transgenic rodent models, gene silencing (both specific and non-specific) has improved disease pathology, even after symptom onset

Answer 19

Drouet et al., 2009, Harper et al., 2005

Question 20

One study showed transient infusion may have sustained benefit - would not need constant tx

Answer 20

Kordasiewicz et al., 2012

Question 21

Recent trial (IONIS-HTTrx) efficiently reduced mutant HTT and did not show adverse effects

Answer 21

Tabrizi et al., 2018

Question 22

Types of HD models

Answer 22

Cell lines, invertebrates, stem cells, mouse models

Question 23

Cell lines

Answer 23

Immortalised cells of human or non human origin. Easy to manipulate and can be used to dissect molecular machinery involved

Question 24

Invertebrates

Answer 24

Whole organism, simpler genetic manipulation with quick reproduction. Used to understand pathways in whole animal (systems level vs reductionist)

Question 25

Stem cells

Answer 25

Can be generated from patient fibroblast cells. Induced pluripotency to generate neurons. Directly can test tx on patient cells

Question 26

Types of mouse models

Answer 26

N-terminal transgenics, Full length transgenics, Knock-ins

Question 27

Adv of N-terminal

Answer 27

Usually have more severe symptoms that develop earlier - quick research

Question 28

Adv of full length

Answer 28

Usually have milder symptoms that develop later - closer to human disease.
Allow therapies to be tested on full human HTT gene

Question 29

Knockins are similar in phenotype to…

Answer 29

Full length

Question 30

N-terminal transgene phenotypes

Answer 30

MANY - range of phenotypes (e.g. loss of coordination, tremor, hypokinesia, abnormal gait…) and expansion lengths. Reviewed by Pouladi et al., 2013

Question 31

Full-length transgenics

Answer 31

Human HTT gene is carried in yeast or bacterial artificial chromosomes (YAC or BAC). Integrate at a single genomic locus. Sx develop slowly - more human-like phenotype.
Allows therapies to be targeted at human HTT gene. Large variance in phenotype

Question 32

Knock in mice

Answer 32

Homologous recombination techniques using mouse embryonic stem cells. Specified number of CAG repeats are introduced directly into the mouse HTT gene. Can be heterozygous - adv as WT HTT may contribute to disease. ESCs are grown on selective media so that only the ones carrying transgene survive, injected into blastocyst then into pseudopregnant female.