Treatment Of Genetic Diseases

Front 1

Out of all genetic conditions, which is most amenable to treatment? What are some treatment options for these conditions? Give examples of a disease that uses each.

Back 1

Metabolic conditions

TREATMENT OPTIONS:
• Avoidance (ex: Barbiturates in Acute intermittent porphyria)
• Dietary restriction (ex: Phenylalanine in PKU)
• Replacement (ex: Thyroid hormone in Congenital hypothyroidism)
• Diversion (ex: oral resins in familial hypercholesterolemia heterozygotes) → divert the pathway, prevent buildup of LDL
• Inhibitions (ex: Lovastatin in familial hypercholesterolemia heterozygotes) → reduce production of LDL
• Depletion (ex: LDL apheresis → direct removal of LDL from plasma in familial hypercholesterolemia HOMOZYGOTES)

Front 2

What is diversion? Give two examples.

Back 2

When a metabolic disorder leads to a build up of a toxic product, diversion is the enhanced use of an alternative metabolic pathway (one that does not normally occur in the body) to reduce the amount of the harmful metabolite. Example: 1.) UREA CYCLE DEFECTS. 2.) FAMILIAL HYPERCHOLESTEROLEMIA

In urea cycle disorders the ammonia (NH3) can’t complete the cycle to produce urea. The buildup of ammonia is toxic to the brain, so treatment involves a diversion that is achieved by administration of SODIUM BENZOATE. The NH3 reacts with Glycine + benzoate → Hippurate (which is excreted in the urine).

Similar plan for familial hypercholesterolemia: Cholesterol is diverted to bile acids and reabsorption in the gut is inhibited. In addition, it is necessary to administer a statin (HMG coA reductase inhibitor) in order to prevent the endogenous formation of cholesterol.

Front 3

When would you do a Depletion for treatment of a genetic disorder? Give two examples.

Back 3

When diseases are caused by accumulation of a compound, treatment to remove that compound is necessary.

EX: plasmapheresis for LDL receptor deficiency (homozygous familial hypercholesterolemia)

OR
Phlebotomy in hereditary hemochromatosis (accumulation of Iron) → draw blood (become a blood donor, or leeches … either way)

Front 4

What is cofactor treatment? Give two examples.

Back 4

Vitamins are often cofactors in enzymatic processes. It may need to be delivered exogenously if there is a cofactor deficiency or a mutant enzyme. Mutant enzymes may have problems binding to the endogenous cofactor, but if you overwhelm the system with huge dosages of the cofactor (given exogenously), then the enzyme may regain some function.

EX: Homocystinuria treated with B6 (pyridoxine)

OR

PKU → administer huge amounts of BH4 to convert phenylalanine to tyrosine.

Front 5

What are some examples of diseases that you might treat by modifying gene expression, and how would you accomplish it?

Back 5

NOTE: does not ALTER genes, but revs up (or alters) expression

• Sickle cell and thalssemia → Butyrate therapy to stimulate expression of fetal Hb genes, this decreases methylation in HbF.
• Also, for thalssemia and “storage diseases” → bone marrow transplant
• Alpha antitrypsin deficiency → liver transplant
• Heriditary angioedema → danazol increases expression of the mutated C1 esterase inhibitor

Front 6

What is the idea behind RNA interference, and what kind of genetic diseases would you theoretically use it for?

Back 6

This would be done for dominant negative mutations. It is not done clinically yet, but the idea is to introduce an RNA that would initiate degradation of only the mutant allele. The whole idea behind a dominant negative mutation is that the mutated gene product loses its own intended function, but also adversely affects NORMAL gene products in the cell. So they key is not just to fix the mutated gene, but GET RID OF the bad gene.

Front 7

What is butyrate treatment?

Back 7

Used to treat sickle cell to increase expression of Fetal hemoglobin, hopefully to dilute out all the mutated hemoglobin.

Front 8

What is SMA. What gene is mutated? How does genetic variances affect the severity of the disease? What is a possible treatment modality for this disease?

Back 8

SMA = Spinal muscular atrophy, defect in anterior horn cell in spinal cord. Caused by a mutation in the Survival Motor Neuron gene. There are two copies of this gene in the genome; the second arose via gene duplication. SMN1 is located in the telomere, SMN2 is located in the centromere.

Key here is that SMN1 and SMN2 are almost identical, except SMN2 is missing a splice enhancing site. In the absence of the splice enhancer, 90% of SMN proteins made by SMN2 are missing an exon and are therefore unstable and rapidly degraded. SMN1 doesn’t have that problem, so this gene is responsible for producing the majority of SMN protein.

All people with SMA are missing the SMN1 gene. BUT it is possible to have more than one SMN2 genes. Therefore, the severity of the disease is based on how many copies of SMN2 genes you have. (Thus a potential treatment would be enhancing SMN2 expression via SODIUM PHENYLBUTYRATE.)

Front 9

What is Curcumin? What disease is it used to treat?

Back 9

Circumin (made from CUMIN) is used to treat cystic fibrosis (specifically DELTA 508 mutations). It inhibits a calcium pump in the endoplasmic reticulum and prevents binding of a Ca++ dependent chaperone to DELTA 508 mutant CFTR. (It keeps the mutated protein from getting stuck in the RER, which is what causes a lot of the problems in this type of CF.) Somehow, the mutated CFTR can then be trafficked to the membrane with this therapy, whereas normally it gets stuck in the golgi.

Front 10

What are aminoglycosides? How might they be used therapeutically?

Back 10

Aminoglycosides are ANTIBIOTICS that can be used to suppress premature termination codons → they incorporate an amino acid at a nonsense mutation to allow translation to continue. This can be effective in diseases involving nonsense mutations (such as cystic fibrosis and duchenne’s muscular dystrophy).

Front 11

What kind of therapy can be used for misfolded protein diseases?

Back 11

Pharmacological chaperones (PC) is a possible treatment for misfolding diseases. diseases (a huge list of diseases, such as CF, long QT syndrome, Tay-Sach’s, Glycogen storage disease, etc.).

**Specific example given in lecture: AT2101 chaperone given to patients with Gaucher disease (a lysosomal storage disease).

Front 12

What is protein replacement therapy? What are its central limitations?

Back 12

Protein replacement therapy can theoretically replace missing proteins for DEFICIENCY diseases (ex: alpha 1 antitrypsin, hemophilia, etc). BUT is often impractical because the protein must either work extracellularly or be able to be somehow internalized into the appropriate cell. This is expensive, may require frequent infusions, may be difficult to manufacture, and may be limited by the production of antibodies to the administered protein.

Front 13

What is enzyme replacement therapy (ERT) and what kinds of diseases is it currently used for?

Back 13

ERT provides RECOMBINANT versions of the deficient enzyme via regular IV infusion. It is currently used for LYSOSOMAL STORAGE DISORDERS. (MPS 1, MPS II, MPS VI, Gaucher disease, Fabry disease, Pompe disease.)

Front 14

What are 6 possible vectors for gene therapy?

Back 14

• Retroviruses
• Adenovirus
• Adeno-associated virus
• Naked DNA
• Liposomes
• Artificial chromosomes