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GENETIC SCREENING & GENE THERAPY
Dr. Dinesh T
Junior resident,
Department of Physiology,
JIPMER
Genetic screening & Gene therapy
Dr sclero dinesh
Introduction
Genetic screening
Counseling
Gene therapy
HistoryTechnology to detect and treat inborn diseases -
1961. 1972 Friedmann and Roblin authored a paper in
Science titled "Gene therapy for human genetic disease?“
The late 1980's, an international team of scientists began the project to map the human genome.
September 14, 1990 - first approved gene therapy case in the United States took place.
1992 - Doctor Claudio Bordignon, Milan, Italy performed the first procedure of gene therapy using hematopoietic stem cells.
1995 DNA testing in forensic cases gains fame in the O.J. Simpson trial.
2002 - first successful gene therapy treatment for adenosine deaminase-deficiency (SCID)
2003 – at University of California, Los Angeles research team inserted genes into the brain using liposome coated in a polymer called polyethylene glycol
2006 - Preston Nix from the University of Pennsylvania School of Medicine reported on VRX496, a gene-based immunotherapy for the treatment of human immunodeficiency virus (HIV) that uses a lentiviral vector for delivery of an antisense gene against the HIV envelope
2007 – Moorfields Eye Hospital and University College London's Institute of Ophthalmology announced the world's first gene therapy trial for inherited retinal disease
2008 there were more than 1,200 clinically applicable genetic tests available.
Genetic screening
What is genetic screening?
The newest and most sophisticated of the techniques
used to test for genetic disorders.
One of the fastest moving fields in medical science.
A technique to determine the genotype or phenotype of
an organism.
Determines risk of having or passing on a genetic
disorder.
Genetic screening
Genetic screening is often used to detect faulty or
abnormal genes in an organism
Can detect some genes related to an increased
risk of cancer
Can detect some genes known to cause genetic
disorders
Genetic tests
The analysis of chromosomes (DNA), proteins,
and certain metabolites in order to detect
heritable disease-related genotypes, mutations,
phenotypes, or karyotype for clinical purposes.
Gene tests (also called DNA-based tests), in a broader sense
Direct examination of the DNA molecule Biochemical tests for such gene products as
enzymes and other proteinsMicroscopic examination of stained or fluorescent
chromosomes
Genetic tests
Who can order?What are the samples needed?How to interpret the tests?What are all the risks?Ethical considerations?
Types of screening tests• Carrier screening
• Prenatal diagnostic testing
• Newborn screening
• Pre symptomatic testing for predicting adult-onset
disorders such as Huntington's disease
• Pre symptomatic testing for estimating the risk of
developing Adult-onset cancers and Alzheimer's disease.
• Conformational diagnosis of a symptomatic individual
• Pre implantation genetic diagnosis
• Forensic/ identity testing
• Research
• Pharmacogenomics
Genetic screening Adult Polycystic Kidney Disease Alpha-1-antitrypsin deficiency Amyotrophic lateral sclerosis Alzheimer's disease Ataxia telangiectasia Central Core Disease Charcot-Marie-Tooth disease Congenital adrenal hyperplasia Cystic fibrosis Duchenne muscular dystrophy/Becker
muscular dystrophy Dystonia Emanuel Syndrome Fanconi anemia, group C Factor V-Leiden Fragile X syndrome Gaucher disease Hereditary Hemochromatosis
Huntington's disease Hereditary nonpolyposis colon cancer Hemophilia A and B Inherited breast and ovarian cancer Marfan Syndrome Mucopolysaccharidosi Myotonic dystrophy Neurofibromatosis type 1 Phenylketonuria Polycystic Kidney Disease Prader Willi/Angelman syndromes Sickle cell disease Spinocerebellar ataxia, type Spinal muscular atrophy Tay-Sachs Disease Thalassemias Timothy Syndrome Galactosemia
Methods for prenatal screening
Pre natal screening
Invasive
Amniocentesis Chorionic villous biopsy
Fetal blood sampling from maternal blood
Non invasive
Ultra sonogram
Maternal serum markers
Pre implantation
• Abnormal results in prenatal screening
• Previous child with a chromosome abnormality
(probability of translocation carrier in parents)
• Family history of a chromosome abnormality
• Family history of a single gene disorder
• Family history of neural tube defect or other
congenital abnormalities
Indications for prenatal diagnosis
Maple Syrup Urine Disease
Congenital Adrenal Hyperplasia
Congenital Hypothyroidism
Glactosemia
Biotinidase Deficiency
Homocystinuria
Phylketonuria (PKU)
Sickle cell and Other Hemoglobinopathies
Newborn Screening Tests:
Pre implantation Genetic Diagnosis (PGD)
Pre implantation Genetic Diagnosis (PGD) uses in vitro fertilisation (IVF) to create embryos.
Tests one or two cells from each embryo for a specific genetic abnormality.
Identifies unaffected embryos for transfer to the uterus.
The approach through PGD assists couples at risk of an inherited disorder to avoid the birth of an affected child without going through selective pregnancy termination.
Pros and cones of gene testing
• To clarify a diagnosis and direct a physician
• To avoid having children with devastating diseases
• Identify people at high risk
• Provide doctors with a simple diagnostic test
• Transforming it from a usually fatal condition to a treatable one
• Possibility of laboratory errors
• Potential for provoking anxiety, and risks for discrimination
social stigmatization could outweigh the benefits of testing
Genetic counseling
• The process by which patients or relatives, at risk of an inherited disorder, are advised of the consequences and nature of the disorder, the probability of developing or transmitting it,
•This complex process can be seen from diagnostic (the actual estimation of risk) and supportive aspects.
Genetic counseling
• Conception (i.e. when one or two of the parents are carriers of a certain trait)
• During pregnancy (i.e. if an abnormality is noted on an ultrasound or if the woman will be over 35 at delivery) • After birth (if a birth defect is seen)
• During childhood (i.e. if the child has developmental delay)
• During adulthood (for adult onset genetic conditions such as Huntington’s disease or hereditary cancer syndromes).
When can we do counseling?
•The couple should be counselled by a genetic
counsellor to inform them of the test results and the
risks to the foetus.
•Providing the options open to them in
management and family planning in order to
prevent, avoid or ameliorate it.
•Autonomy of decision is crucial.
•The ethical, legal, and religious issues should be
respected.
• A type of genetic test that is accessible directly to the consumer without having to go through a health care professional.• A variety of DTC tests, ranging from testing for breast cancer alleles to mutations linked to cystic fibrosis. • Benefits of DTC testing are the accessibility of tests to consumers, promotion of proactive healthcare and the privacy of genetic information.• Risks of DTC testing are the lack of governmental regulation and the potential misinterpretation of genetic information.
Direct-to-Consumer (DTC) genetic testing
Gene therapy
Gene therapy is the replacement of faulty genes.
Introduction of functional
genetic material into target
cells to replace or
supplement defective
genes, or to modify target
cells so as to achieve
therapeutic goals.
In theory it is possible to transform either somatic
cells (most cells of the body) or cells of the germ
line (such as sperm cells, ova, and their stem cell
precursors).
• All gene therapy so far in people has been
directed at somatic cells.
• Germ line engineering in humans remains only a
highly controversial prospect.
For the introduced gene to be transmitted
normally to offspring, it needs not only to be
inserted into the cell, but also to be incorporated
into the chromosomes by genetic recombination
Somatic Cell Therapy
This is when a gene is introduced into a
patient to help them recover from a
disease.
Germ Line Therapy
Changes are made to genes that will affect
subsequent generations.
Applications of Gene Therapy
Radical cure of single gene diseases e.g.
cystic fibrosis, haemoglobinopathies.
Amelioration of diseases with or without a genetic
component e.g. malignancies, neurodegenerative
diseases, infectious diseases.
Gene therapy concerns
Vectors in gene therapy: Viruses
Retroviruses
Adenoviruses
Adeno-associated viruses
Envelope protein pseudotyping of viral vectors
Non-viral methods
Naked DNA
Oligonucleotides
Lipoplexes and polyplexes
Hybrid methods
A new gene is inserted into an adenovirus vector, which is used to introduce the modified DNA into a human cell. If the treatment is successful, the new gene will make a functional protein.
Gene therapy using an adenovirus vector.
Non viral vectors
Un complexed plasmid DNA
DNA coated gold particles
Liposomes
DNA – protein conjugates
Modes of introducing genetic material
Modes
Physical methodsGene gun
Sonoporation
Electroporation
Hybrid methods
Chemical methods
Oligonucleotides
Lipoplexes
Dentrimers
Un complexed Plasmid DNA
Purified DNA or mRNA injected directly
into tissues
Injected into muscle and skin
• Utility in immunization/ vaccination against
Infectious diseases
• Ectopic synthesis of therapeutic proteins
as erythropoietin.
DNA coated Gold particles
• Plasmid DNA + Gold particles ( 1 micron india)
• “shot” into cells using electric spark or
pressurized gas – “gene gun”
• Epidermis
• Skin tumours (melanomas)
• Gene mediated immunization
Liposomes
• DNA surrounded by hydrophobic molecules
• Anionic – given i.v. Targets reticuloendothelial cells of
liver
• Cationic – transgene expression in most tissues if given
in afferent blood supply
• Intra airway injection or aerosol to target -lung epithelium
DNA- Protein conjugates
• Cell- specific DNA delivery systems
• Utilize unique cell surface receptors on
target cells
• Chemical cross linking methods used
• A normal gene may be inserted into a nonspecific location within the genome to replace a nonfunctional gene.
• An abnormal gene could be swapped for a normal gene through homologous recombination.
• The abnormal gene could be repaired through selective reverse mutation, which returns the gene to its normal function.
•The regulation (the degree to which a gene is turned on or off) of a particular gene could be altered.
Methods
• In vivo
Suspension containing vector is injected
directly into the patient either systemically (i.v.)
or directly into target tissue (e.g. malignant
tumour)
• Ex vivo
Target cells (stem cells,myoblasts,fibroblasts
etc) removed from the patient, treated with
vector and injected back into the patient
Gene Transfer techniques
Spectrum of gene expression
Gene replacement for single gene disorders
Gene repair
Gene inactivation
Ectopic synthesis of therapeutic proteins
Cancer gene therapy
A) Immunodeficiency Disorders
Adenosine Deaminase Deficiency
X- linked SCID
Chronic Granulomatous disease
B) Liver Disease
Familial Hypercholesterolemia
Haemophilia A
Target diseases
Hemoglobinopathies
D) Lung Diseases
• Cystic Fibrosis
• α- 1 Antitrypsin Deficiency
E) Skeletal Muscle
• Duchene Muscular Dystrophy
• Limb Girdle Muscular Dystrophy
Challenges• Short-lived nature of gene therapy
• Difficult to treat multi gene or multi factorial disease
• Inserting gene into correct cells.
• Controlling gene expression. Possibility of over expression
• Damage to the host gene
• Acquirement of virulence
• Chance of inducing a tumour (insertional mutagenesis)
Conclusion
Thank u all….
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