Emerging Treatments Flashcards
(28 cards)
What are inborn errors of metabolism?
Largest group genetic disease and affects variety of pathway. Lack enzyme > can’t make product > leads to excess substrate > leads to alternative product. Examples of this are: PKU, MCAD Deficiency, Maple Syrup Urine Disease, Homocystinuria
What causes phenylketonuria?
Caused by lack of phenylalanine hydroxylase (enzyme) so phenylalanine can’t be converted to tyrosine and instead is converted to phenylketones. It also affects the creation of melanin.
What are symptoms of PKU? How is it treated?
Major cognitive impairment, Behavioural difficulties, Fairer skin, hair and eyes compared to siblings due to lack of melanin and recurrent vomiting. Phenylketones are neurotoxic and kill brain cells causing the symptoms. Treated with a low protein diet and tyrosine supplement.
What did finding treatment for PKU prove?
Before treatment, the cause must first be identified. However, it is possible to develop treatment before gene identified through knowing the biochemistry of disease.
What are the symptoms of haemophilia?
Uncontrolled bleeding, Bleeding into joints, Excruciating pain, Bleeding into brain, Internal bleeding. Fatal if untreated.
What scandal occured with haemophilia?
In the 1970-1980s, 5000-30000 given clotting factors contaminated with HIV and hepatitis. 2500 so far died. Hence, in 1980s - heat treat products kill virus and Factor VIII gene cloned. 1990s – Recombinant Factor VII treatment available so blood transfusion not required.
What diseases are treated with replacement?
Growth hormone deficiency - Injection growth hormone now recombinant (cadaver derived cjd was initially an issue)
Lyosomal storage diseases – effect lysosomal breakdown
Fabry disease - Injection recombinant alpha galactosidase A
Pompe disease - Injection of alpha glucosidase
What are the different methods of treatment without knowing the genetic cause and what else needs to be known?
Can treat by diet or replacements. But need to know biochemistry - if known, genetic cause not required and treatment doesn’t need to be mutation specific.
What are pharmacological chaperones and when are they used?
Protein folding is complex and sometimes fails. The system in endoplasmic reticulum degrades misfolded proteins and hence mutations which prevent proteins folding properly lead to these proteins being subjected to the degradation pathway.
If folded correctly would be active. Chaperones can stabilise the shape of the protein so it folds properly and does not get degraded. (It acts as a competitor to the original defective enzyme)
Provide an example where a pharmacological chaperone is used
Fabry disease is caused by a deficiency of alpha-galactosidase A which leads to a build-up of globotriaosylceramide. However, some mutations can simply cause a misfolding of the original enzyme and in these cases, Miglastat is used which is a small chaperone molecule. This stabilises the enyme in the correct shape but is mutation specific. NICE approved in Feb 2017.
What is a pharmacolgical modulator and when is it used?
Pharmacological modulators are commonly used drugs. These are receptor agonists/antagonist and Ion channel activators/blockers. Can design one that has these effects on mutant receptor or channel such as the Bcl-abl Kinase inhibitors (Philadelphia chromosome)
Provide an example where a pharmacological modulator is used
Used in treatment of Cystic fibrosis. CF causes defective chloride channel and mutations (33) cause channel not to open. Ivacaftor is a drug which causes activation of these channels but is mutation specific.
What is combination therapy and when is it used?
In the case of CF, fefective chloride channel and a particular mutation (f508del) result in misfolded, inactive channel. Treated with combination chaperone and activator (turns it on in situations when it wouldn’t be on). Orkambi (Ivacaftor/lumacaftor) is a combination of both – NICE approved Oct ’19. This is not a cure but does improve lung function.
What are non-sense mutations and what do they cause? How are they treated?
Non-sense mutations are when there is a premature stop codon preventing protein production. Aminoglycoside antibiotics bind to ribosome causing mistranslation so skip the nonsense in a loss of function.
When can reading through be an advantage?
There are two types of MD:
Duchenne muscular dystrophy – caused by premature stop
Becker muscular dystrophy – caused by a missing section
If the premature stop codon is read through, then DMD → BMD, which has a less severe phenotype.
Ataluren – approved in EU not in US
NICE approved – June 2016
This is non-sense mutation specific
What are the 2 aims of gene therapy and 3 types?
Aims if disorder caused by:
Recessive disease - replace defective gene
Dominant disease – delete defective gene
3 types are: in vivo, ex-vivo and in-vitro. In vivo gene therapy means that therapy is administered directly the patient. The targeted cells remain in the body of the patient. With ex vivo gene/cell therapy the targeted cells are removed from the patient and gene therapy is administered to the cells in vitro before they are returned to the patient’s body.
Why is gene therapy difficult to successfully carry out?
Problems:
- Achieving specificity
- Getting therapy to right place
- Maintaining expression
Much easier to achieve in vitro than in vivo
How is in vivo gene therapy carried out?
Viral vector introduced by systemic adminstration intravenously or intra-parenchymal adminstration in brain, liver.
How is ex vivo gene therapy carried out?
Patient’s cells collected and HSCs isolated. Therapeutic gene inserted into inactivated virus and mixed with patient’s cells, restoring healthy genotype. Tranduced stem cells reintroduced into patient.
What does mitochondrially inherited disease therapy involve?
Requires IVF where DNA taken from fertilised patient egg and this is transferred to a donor egg with normal mitochondria. Approved for use in UK but has some controversy.
What is virus gene therapy?
Relies on engineering viruses to carry a therapeutic gene – AAV used, adenovirus, lentivirus (HIV), vaccinia. Virus choice depends on tissue you want to treat and amount of DNA is limited as it depends on the virus – viral tropism: affinity of virus for infecting certain cell types.
What is SCID?
Stands for severe combined immune-deficiency: Bubble baby disease. This is when person lacks both B-cell and T-cell mediated responses. There are several forms: most common is X-linked (in 70% of cases) but can also be due to Adenosine Deaminase deficiency (ADA-SCID 15%).
How is SCID treated with gene therapy?
Can be treated with bone marrow transplant but not possible for all children as 80% of ADA-SCID no match + has own risks
Strimvelis – in vitro gene therapy for ADA-SCID, involving an autologous transplant where you take bone marrow from a patient and isolate haemopoietic stem cells, esp CD34 positive ones, and expand them. Transfect these cells with lentivirus encoding ADA and grow these cells. Meanwhile, treat patient with busulfan to kill their HSCs and then reinfuse transformed cells into patient. New ones with ADA replace the old dysfunctional ones.
What is an example of in vivo therapy supplement?
Lack of a gene can be remedied by using a virus to carry the missing gene into the cell. Example is Leber congenital amaurosis, recessive disease caused by mutation RPE65 and entails loss of retinal cells. Luxturna rAAV2 sent in with gene so RPE65 is expressed.
