Principles of therapy of hereditary diseases

Gene therapy options for a number of diseases are currently being explored.

Germ gene therapy[edit | edit source]

intervention in the gamete, zygote or embryonic cells at a very early stage of development
genetic change is found in all cells of the newly formed organism
The influence of bb, from which gametes are formed , is therefore transmissible to offspring
we cannot estimate the results in future generations of, ethical barriers before performing germline gene therapy

Somatic gene therapy[edit | edit source]

performing a genetic change in somatic calls, or tissues
tissues are selected according to the type of disease
manipulation in cells can be performed ex vivo, in vivo
Ex vivo = cells are harvested into a suitable environment and returned after therapy
In vivo = suitable for bb, which is impossible to cultivate or return to the body

the vector carrying the gene could be inserted directly into the tissue
the success of these experiments is very low
most suitable bb for gene therapy -long life, proliferate, can be easily obtained
Bone marrow stem cellsare an example - but they are poorly insulated

Somatic cell modification[edit | edit source]

Several approaches:

introducing a functional copy of the gene into bb, the mutant gene remains unchanged
repairing the mutant gene or placing a working copy of the gene in place of the mutant gene
targeted inhibition of gene expression
targeted destruction of specific cells (significant in tumors)
destruction of specific cells of the immune system

The goal is long-term expression of the introduced gene.

Thus, the foreign gene must integrate into the chromosome of the host cell, and bb must have the ability to further divide. The foreign gene is then transferred to the daughter cells - the gene integrates differently, o it is located in other places in subsequent cycles.

Viral vectors[edit | edit source]

viruses have developed efficient systems for inserting their genomes into human bb
the virus must be modified so that its genome does not harm the human cell
most of the viral genome is deleted, replaced with human promoter and regulatory regions
high efficiency

Retroviral vectors[edit | edit source]

the genome of retroviruses jonsists of RNA, contains 3 genes (gag, pol, env) and the sequence phi, which is recognized by viral proteins - assembly of the viral particle
they have their own reverse transcriptase
upon entry into the host cell during division (membranes are disrupted)
cDNA attaches to host information při dělení (jsou porušené membrány)
the cloning capacity is 8 kb
The human gene vector is introduced into special cells that make many copies of human sequence retroviruses
modified retroviruses are then incubated with the patient's somatic cells (lymphocytes)
the human gene is inserted into the DNA of the host cells with high efficiency
disease : severe combined immunodeficiency (SCID)

Adenoviral vectors[edit | edit source]

dsDNA remains in the nucleus of a human cell, but does not integrate into its genome
the vector must be modified as well as the retrovirus
infect bb that do not divide (respiratory system)
cystic fibrosis – therapy - human CFTR gene in adenovirus - modified virus was applied to the epithelial airway in the form of an aerosol
low potency, only transient gene expression

Adeno-associated viral vectors[edit | edit source]

ssDNA, the replication of which depends on the presence of the virus
do not elicit any immune response
as adenoviruses can infect undivided se bb
hold a small insert – 5kb
factor IX vector for people with hemophilia B

Lentiviral vectors[edit | edit source]

complex retroviruses , can also infect non-dividing bb
holes in the nuclear envelope enter the nucleus
cloning sequence approx. 8 kb
antivirus = e.g. HIV

Problems associated with viral gene therapy[edit | edit source]

transient expression, low gene expression
difficult to obtain specific bb, tissues (neurons)
the need for precise regulation of gene activity
potential danger of tumor transformation of the cell (accidental insertion of the virus into the cell may affect the expression of a minor gene, which may be a proto-oncogene)
immune response of the organism against the viral vector

Non-viral vectors[edit | edit source]

direct injection of DNA into tissue
firing of metal particles , that contain DNA
the association of DNA with a molecule that is bound by receptors to the cell surface is followed by endocytosis
very low efficiency in these methods

Liposomes[edit | edit source]

artificially formed phospholipid bilayer , particles that can hold a relatively large DNA insert
they can fuse with the cell, transferring the DNA insert into the cytoplasm
they do not contain peptides = they do not elicit an immune response

Blockade of gene expression[edit | edit source]

gene products function in complexes of molecules (dimers)
the mutated protein in the complex may affect their function
inhibition of transcription does not result in gene expression
replacement of gene damage by homologous recombination

disease	target cells	product advertisement
SCID	lymfocytes, bone marrow stem cells	adenosin deaminase
hemophilie B	hepatocytes	factor IX
cystic fibrosis	epithelium. Bb airways	CFTR
familial hypercholesterolemia	hepatocytes	LDL receptor
Duchenne muskular dystrophy	myoblasts	dystrophin
AIDS	TH lymfocytes	retroviral mutation

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Gene therapy
- eg. transformation by cloned genes
  - disease: adenosine deaminase deficiency (severe combined immunodeficiency )^[1]
Enzyme induction
- eg barbiturates
  - disease: congenital non-hemolytic jaundice (see differential diagnosis of jaundice)
Enzyme replacement
- eg tissue transplantation
  - disease: mucopolysaccharidosis
- eg enzyme substitution
  - disease: trypsin deficiency
Protein substitution
- eg antihemophilic globulin
  - disease: hemophilia
Vitamin substitution
- eg. vitamin D
  - disease: vitamin D resistant rickets
Product substitution
- ex cortisone
  - disease: adrenogenital syndrome
- eg thyroxine
  - disease: congenital hypothyroidism
Substrate restriction in the diet
- eg. AMK – Phenylalanin
  - disease: phenylketonuria (see Poruchy metabolismu aromatických a větvených aminokyselin)
- eg sugars - galactose
  - disease: galactosemia
- eg fats - cholesterol
  - disease: hypercholesterolemia (see Disorders of aromatic and branched chain amino acid metabolism ))
Drugs that reduce the excess product of defective metabolism
- eg. cholestyramin
  - disease: hypercholesterolemia (obsolete in the era of statins)
- eg. penicilamin
  - disease: M.Wilson
Replacement of the institution
- eg kidney transplantation
  - DISEASE: polycystic kidney disease
Removal of organ
- eg colectomy
  - disease: familial colon polyposis