Emerging Treatments

Question 1

What are unborn errors of metabolism?

Answer 1

Largest group of genetic disorders
Affect variety of pathways e.g. carbohydrates, fatty acids, protein metabolism
They’re caused by lack of an enzyme in that pathways which leads to increased substrate levels

Question 2

What is phenylketonuria (PKU)?

Answer 2

Lack of phenylalanine hydroxylase which is needed for phenylalanine to tyrosine conversion
Instead we get phenylalanine to phenylketones

Question 3

What are symptoms of untreated PKU genes?

Answer 3

Major cognitive impairment
Behavioural difficulties
Fairer skin, hair and eyes- lack of melanin
Recurrent vomiting

Question 4

How is PKU treated?

Answer 4

Treated with low protein diet

Tyrosine supplements

Question 5

What is haemophilia?

Answer 5

Blood clotting disorder- causes uncontrollable bleeding
Bleeding occurs in joints which causes excruciating pain
You can get bleeding into brain and internal bleeding

Question 6

What haemophilia treatments are there?

Answer 6

Cryoprecipitate transfusion:
FVIII concentrate
Freeze-dried plasma-derived factor concentrates

Question 7

What is the haemophilia blood scandal?

Answer 7

1970-1980
3000- 5000 given clotting factors contaminated with HIV and Hepatitis
2500 died so far

Question 8

How are clotting factors now treated to make them safe for transfusion?

Answer 8

Use of recombinant factor VIII treatment- genetically engineered
Donor and blood screening
Heat treated product to kill virus

Question 9

What other diseases are treated by replacement therapy?

Answer 9

Growth hormone deficiency- GH now recombinant
Lysosomal storage diseases- effect lysosomal breakdown e.g. Fabry’s disease (treated with recombinant alpha galactosidase A) and pompe disease (treated with alpha glucosidase)

Question 10

Who approves drugs for the NHS?

Answer 10

England and Wales: National institute for health and care excellence (NICE)
Scotland: Healthcare improvement Scotland

Question 11

What are pharmacological chaperones?

Answer 11

Protein folding is complex and sometimes fails
System in ER degrades misfolded protein
A pharmacological chaperone binds to the misfiled protein and folds it into the correct shape

Question 12

What is an example of a pharmacological chaperone?

Answer 12

In Fabrey’s disease theres a deficiency of alpha galactosidase A
This leads to a build up of globotriaosylceramide
Migalostat is a small molecule chaperone,
It binds to the misfolded enzyme and stabilises the enzyme in the correct shape
Mutation specific

Question 13

What are pharmacological modulators?

Answer 13

Receptor agonists/ antagonists
Ion channel activators/ blockers
Have an effect on a specific mutant channels or receptors

Question 14

What is an example of a pharmacological modulator?

Answer 14

Cystic fibrosis leads to defective chloride channels - mutation causes channel not to open
Ivacaftor is a drug designed to open these channels
It’s mutation specific

Question 15

What is an example of combination therapy?

Answer 15

Some cases of CF are due to mutation as a cause of misfolding which leads to inactive channel
They’re treated with a combination of chaperone and activator (pharmacological modulator)
e.g. Orkambi (Ivacaftor / lumacaftor)

Question 16

How do drugs cause stop codon read through?

Answer 16

Some diseases are caused by a non-sense mutation- premature stop codon
This prevents protein production
Aminoglycoside antibiotics bind to 30S ribosome subunit and cause mistranslation - it reads through the stop codon

Question 17

What is an example of a stop codon read through drug?

Answer 17

Duchenne muscular dystrophy is a result of a premature stop codon
Becker MD is caused by a missing section
If we read through the premature stop in DMD we get BMD
E.g. Ataluren
Non-sense specific mutation

Question 18

What are mitochondrially inherited disease therapies?

Answer 18

Performed In- vitro
Takes DNA from fertilised egg that has mutated mitochondrial DNA
Transfer to donor egg with nucleus removed
Fused egg is fertilised in vitro
Its known as 3 parent babies

Question 19

What is virus gene therapy?

Answer 19

We can engineer viruses to carry therapeutic gene
Wide variety of uses: Adenovirus, lentivirus
Virus choice depends on target tissue

Question 20

What is SCID?

Answer 20

Severe combined Immuno-deficiency
Bubble boy disease
Lack both B and T cell mediated response
Severe forms includes: X- linked SCID and Adensosine deaminase deficiency (ADA-SCID)

Question 21

How is SCID treated?

Answer 21

Can be treated with bone marrow transplant

Not possible for all children however

Question 22

What therapy is used for ADA-SCID?

Answer 22

Treatment called strimvelis
Autologous transplant 
Isolate patient's haematopoietic stem cells
Isolate and expand CD34+
Transfect with ADA- lentivirus
Grow transformed cells
Treat patient with busulfan (kills HSC)
Reinfuse transformed cells into patient

Question 23

How do in- vivo therapy supplements work?

Answer 23

There useful for conditions where theres a lack of a functional gene
Uses a virus to carry in a working copy of the gene
Can be injected systemically and injected locally

Question 24

What is an example of a disease treated with in-vivo therapy supplements?

Answer 24

Leber congenital amaurosis type 2
Recessive disease caused by mutation of RPE65
Leads to loss of retinal cells- progressive blindness
Treatment: Luxturna rAAV2 expressing RPE65
Not a cure but improves vision
Patients need sufficient remaining cells

Question 25

How are anti-sense oligonucleotides used for gene therapy?

Answer 25

They’re short modified nucleic acids, complimentary to target
Modification prevents degradation and allows entry to cell
It binds to the target and blocks translation. It can also alter splicing
Relatively cheap to make

Question 26

What is an example of an anti-sense oligonucleotide treatment?

Answer 26

Useful for diseases caused by a gain of function
E.g. inotersen
Used in treatment of transthyretin - related hereditary amyloidosis
Caused by mutation in transthyretin (TTH)
TTH cant form tetramers, this forms aggregates which damage tissues
Inotersin binds to mRNA which encodes mutant transthyretin and degrades them
Slows progression of disease

Question 27

How can anti-sense oligonucleotides be used for exon skipping?

Answer 27

During pre-mRNA processing, oligonucleotides can cause exons to be skipped
This can be used to skip disease causing exon
Anti-sense oligonucleotide binds to acceptor site of exon and blocks it from acting as an acceptor site
Treatment is limited:
- exon skipped must not be vital
- Generally only large proteins

Question 28

What is an example of exon skipping treatment?

Answer 28

In DMD exon skipping used to convert DMD to BMD

E.g. Eteplirsen- oligonucleotide used to skip exon 51. Will result in partially active dystrophin

Question 29

What is CRISPR- cas9

Answer 29

Bacterial system disables bacteriophages (viruses that infect bacteria)
Clustered Regularly Interspaced Short Palindromic Repeats
CRISPR- derived from previous bacteriophage infection in bacteria
Cas9- CRISPR associated protein 9- its an endonuclease so will cut DNA sequences
Recognises and cleaves DNA CRISPR hybrids

Question 30

What is CRISPR-Cas9 used for?

Answer 30

Gene correcting relatively small changes
Cannot correct large changes (deletions, triplet expansion)
Many have off-target effects
Not currently used in humans- controversial and illegal in most of world

Question 31

How has CRISPR-Cas9 been used in in-vitro gene editing?

Answer 31

Used to alter the genome of IVF embryo

Deleted CCR5 in twins