Genetic treatments Flashcards
What are inborn errors of metabolism?
Largest group of genetic diseases.Rare inherited disorders whereby the body is unable to effectively convert substrate into energy or for the synthesis of ATP (Glycolysis, and beta oxidation)
What inheritance pattern is demonstrated by phenylketonuria (PKU)?
Autosomal recessive
Which metabolism is affected by PKU?
Phenylalanine metabolism
Why is phenylalanine metabolism affected by PKU?
There is a deficiency in the enzyme phenylalanine hydroxylase (PAH)
The enzyme catalyzes the amino conversion of phenylalanine into tyrosine
Leads to an accumulation of phenylalanine and its metabolites in tissues and bodily fluids
Explain the pathophysiology of PKU in terms of phenylalanine accumulation?
Elevated levels of Phe, leads to increased production of phenyl ketones, these compounds express degrees of neurotoxicity.
What are the symptoms associated with untreated PKU?
Major cognitive impairments; behavioural difficulties; fairer skin tone, hair and eyes; lack of melanin and recurrent vomiting.
How is PKU treated?
Patients are given a low protein diet (protein diets have high Phe content) - in a combination of Tyrosine supplements
Screening program introduced to measure levels of phenylalanine upon initial recognition of disease; treatment succeeds in scientific understanding.
What is the inheritance pattern of haemophilia?
Sex-linked inherited genetic condition
What is haemophilia?
Blood clotting disorder due to
hereditary lack of coagulation factor VIII
What are some treatments are available for haemophilia ?
Replacement therapy-recombinant factor VIII
How can cryoprecipitate be used to treat haemophilia?
Prepared from plasma & purified, contains factor VIII, and platelet concentrates can be intravenously administered as a replacement therapy
Recombinant clotting factor VIII gene cloned to synthesize an increased level of factor can be used.
How do clotting preserving medications work?
Medications inhibit and reduce fibrinolysis - reducing clot degradation
What is the first phase of drug development?
Drug development relies on multiple phases to ensure efficacy
First stage discovery is based on preclinical understanding (lab-based experimental procedures to provide evidence to back hypothesis)
Animal testing to evaluate toxicity, and clinical testing to identify dosages
How many main phases are there for clinical drug testing?
Phase 1-3
3 phases
What is phase 1 for clinical testing?
Safety in healthy volunteers (<100)
What is phase II during clinical testing?
Check therapeutic effect (100-300)
What is phase III of clinical testing?
Large scale therapeutic trials (200-3000) Approval: EMA & FDA
How are NHS drugs approved?
Prescription of NHS drugs require approval by the National Institute for Health & Care Excellence (NICE) for England & Wales.
Healthcare improvement in Scotland
How are NHS drugs approved?
Depending on cost-effectiveness and efficacy
Provides guidelines for treating conditions
What are pharmacological chaperones?
Correct misfolded proteins which may be caused due to mutations.e.g migalastat stabilises enzyme in correct shape
What are pharmacological modulators?
Are receptor agonists/antagonists behaving through ion channel activation/inhibition
What is the function of the BCL-ABL kinase inhibitor?
Product of Philadelphia chromsome, drug only binds to mutant kinase form
How does the pharmacological modulator, ivacaftor treat cystic fibrosis?
Causes opening of defective chloride channel.Is mutation specific.
How can combination therapy be used to treat cystic fibrosis?
Orkambi involves a combination of chaperone and activator molecules.
Improves lung function but not cure.
How are nonsense mutations caused?
Caused by premature stop codon within the sequence of mRNA. Prematurely truncates the polypeptide chain. Protein is degraded (sensed as incorrect combination).
How does DMD &BMD in terms of deletions and stop codons occur?
DMD Premature stop codon
BMD -> Deletion causes omitted section, dystrophin exhibits partial functionality
If read through premature stop DMD->BMD
In terms of gene therapy what happens in dominant conditions to the gene?
Delete defective gene
In terms of gene therapy what happens in recessive conditions?
Replace defective gene
How can mitochondrial diseases be therapeutically treated in terms of genetics?
Requires IVF, DNA derived from fertilised ovum is extracted and transferred to donor egg normal mitochondria Spindle transfer (unfertilised egg). Spindle complex is removed and transferred to the donor egg, the fused egg is fertilised in vitro
PRONUCLEAR TRANSFER
How do viral vectors work?
Viral genes conferring for proteins that result in stimulating adverse effects are removed or inactivated, and the desired gene is inserted. Thereby, this integrates the desired gene into the viral genome
Lysogenic viruses are used to transfer the desired gene into the cell to be transformed
The recombinant DNA can thus be integrated into the host’s genome
Which viruses are commonly used as viral vectors in the treatment of genetic diseases?
AAV, adenovirus, lentivirus (HIV) and vaccinia
How can SCID be treated?
Involves the removal of T-lymphocytes and insertion of the correct allele into them using a vector. The successful cells are cloned - replenish numbers
What is the inheritance pattern of cystic fibrosis?
Autosomal recessive
Which is the most common viral vector for CF treatment/
Adenovirus
What is germline gene therapy?
Involves changing the genes in cells that would go on to become gametes
What is the inheritance pattern of Leber congenital amaurosis type 2?
Autosomal recessive
What are the symptoms associated with the mutated RPE65 allele?
Results in progressive blindness attributed to a reduction in retinal cells
How can in vivo therapy supplement be used to treat retinal blindness?
Viral vector expressing the correct gene is injected into the retina, replaces defective recessive allele. Patients require sufficient remaining cells
What are anti-sense oligonucleotides?
Antisense oligonucleotides are short modified single-stranded nucleic acids that interact with mRNA to prevent translation of a targeted gene
How do anti-sense oligonucleotides work?
Bind to target mRNa destroying it and blocking translation.
What is in vivo therapy knockdown?
Blocking genes to prevent dominant disease.RNA interference results in downregulating gene expression of the target gene. Useful for diseases caused by gain of function
What is exon-skipping?
Pre-RNA processing oligonucleotides cause exons to be skipped, thereby this skips the disease-causing exon, and enables the RNA to be reintegrated into the reading frame with the removed mutant exon, resulting in partially active protein.
Removed exon cannot be vital to protein function; effective for large proteins (minor impact on polypeptide chain)
Why is exon skipping more effective in large proteins?
Removed exon cannot be vital to protein function; effective for large proteins (minor impact on polypeptide chain)
Which genetic disorder is exon skipping used for?
Duchenne muscular dystrophy; transformed into Becker phenotype
What are the limitations of gene editing?
Gene editing corrects relatively small errors, cannot correct large changes (deletions and triple expansions)
Off-target effects and problems with targeting and getting into cell.
What is in vivo therapy?
A virus is used to carry in a working copy of a gene which is lacking.
What does CRISPR stand for?
Clustered Regularly Interspaced Short Palindromic Repeats
Explain CRISPR-CAs9.
Endonuclease recognises and cleaves DNA CRISPR hydrids.
Where has CRISPR been used.
To delete CCR5 gene in twins in China.
