GENETIC SCREENING & GENE THERAPY Genetic screening & Gene therapy Dr. Dinesh T Junior resident, Department of Physiology, JIPMER Dr sclerodinesh
History Technology 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.
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 increasedrisk of cancer Can detect some genes known to cause geneticdisorders
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 proteins Microscopic 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
Prenatal diagnostic testing
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
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 Fanconianemia, 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 PraderWilli/Angelman syndromes Sickle cell disease Spinocerebellar ataxia, type Spinal muscular atrophy Tay-Sachs Disease Thalassemias Timothy Syndrome Galactosemia
Methods for prenatal screening
Indications for prenatal diagnosis
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
Newborn Screening Tests: Maple Syrup Urine Disease Congenital Adrenal Hyperplasia Congenital Hypothyroidism Glactosemia Biotinidase Deficiency Homocystinuria Phylketonuria (PKU) Sickle cell and Other Hemoglobinopathies
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
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.
When can we do 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
During adulthood (for adult onset genetic conditions
such as Huntington’s disease or hereditary cancer syndromes).
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.
Direct-to-Consumer (DTC) genetic testing
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.
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: Non-viral methods Viruses Adeno-associated viruses Retroviruses Oligonucleotides Hybrid methods Lipoplexes and polyplexes Adenoviruses Naked DNA Envelope protein pseudotyping of viral vectors
Gene therapy using an adenovirus vector. 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.
Non viral vectors Un complexed plasmid DNA DNA coated gold particles Liposomes DNA – protein conjugates
Modes of introducing genetic material
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”
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.
Gene Transfer techniques • 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
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