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….