Genetic Testing and Counseling, and Gene Therapy

By Jeraun Hudson, Brian Smith, and Thomas

Genetic Testing

Newborn screening is integrated into normal medical practice. This type of genetic testing isn’t new….

In 1961, the Guthrie test sampled a newborn’s blood for the buildup of amino acid phenylketonuria (PKU)

Today tandem mass spectrometry used to ID metabolism errors in newborns

Genetic Testing

Then, the polymerase chain reaction is used to help amplify the mutations, making it easier to ID. Today the availability of testing for rare diseases is increasing.

Polymerase Chain Reaction

Types of Tests

Carrier Screen

Prenatal Test

Prenatal Screen

Newborn Test

Diagnostic Test

Predisposition Test

Predictive Test

Types of Tests

In 2005, the U.S. government mandated testing for 29 conditions that are treatable and recommended testing for an additional 5 conditions that are currently untreatable.

Genetic Counseling

Most medical professionals receive very limited training in the field of genetics. The role of genetic counseling is expandingRecent definition: “shared deliberation and decision making between the counselor and the client”Reasons people seek counseling: Prenatal diagnosis Disease in the family

Genetic Counselors

Sessions with a counselor begin with the families’ medical history being summarized in a pedigree, which includes knowledge of the risks of precurrence for other relativesFrom there, they discuss the condition, and try to determine which tests to take, or if assisted reproductive technology is neededOnce the couple decides which tests are appropriate, the counselor must ask if the risks outweigh the benefitsOften, communication can be hard-counselors must be sensitive and respectful, yet give their best opinion on what would be right for the clients

Genetic Counselors

There are only 2,200 genetic counselors in the US with a masters degree, and most practice in urban areas. Access to their services is limited. Other less-qualified professionals have been called in to fill their shoesAs long genetic testing becomes more commonplace medical practice, and more is learned about genes, the need for genetic counselors will continue to rise

Genetic Privacy

Since results of genetic tests may have large impact on a person’s life, they may want to keep such information privateDoctors must weigh the risks and benefits of keeping this info confidential, if doing so may cause harm“Duty to warn”- Doctors must know when it is better judgment to inform someone of a patient’s genetic disease or the risks associated with itCourt cases have brought this issue to the forefrontNow, the AMA mandates a doctor may disclose info if Harm keeping quiet outweighs harm of breaching confidentiality Relatives at risk can be identified Failure to warn places the patient is at great risk

Treating Genetic Disease

Treatment has evolved in 3 phases

Replacing missing proteins w/ donations

Obtaining pure proteins w/ recombinant DNA technology

Delivering replacement genes to correct the problem, also called GENE THERAPYGENE THERAPY

Gene Therapy

Treating the phenotype can be simple, like supplying a missing protein in a person’s diet, or even using corrective eyewear

However, altering genes directly will have a better effect than just treating symptoms

Genetic Therapy

Concerns: Which cells to treat, and how? Is gene overexpression dangerous? Will the immune system attack the

introduced cells? Does the targeted DNA sequence

occur in other genes? Does the participant truly

understand the risks? If effective, how will the recipients

be selected Should rare or more common

disorders be the focus of research and clinical trials?

Requirements: Knowledge of defect and how it

causes symptoms An animal model Success in human cells growing in

vitro No alternate therapies Safe experiments

Gene Therapy

First efforts focused on inherited disorders that researchers knew the most about With the increasing understand of human genes and their

function, gene therapy is nowadays targeting more common illnesses

3 approaches “Ex vivo”-cells altered outside the body, then infused with

corrected gene and returned to the body “In situ”-healthy gene plus DNA delivering it (the vector) are

injected into a localized body part “In vivo”-vector introduced directly into the body

Ex vivo illustration

In vivo illustration

Germline Vs. Somatic

Germline (aka inheritable) gene therapy alters DNA of a gamete or fertilized ovum; all alleles are changed, and passed on to offspring; not used on humans

Somatic gene therapy corrects only the cells an illness affects; the cure isn’t passed on to offspring, and no gametes are altered

Gene Delivery

Three ways Physical: electroporation,

microinjection, particle bombardment

Chemical: liposomes can enclose gene cargo and other lipids that carry DNA across the plasma membrane

Biological: Vector such as a viral genome used, as the viral gene is removed and corrective genes replace it.

Viral genomes: types and treatment

Adeno-associated virus (AAV)– sickle cell, Canavan disease

Adeno virus (AV)– cystic fibrosis, emphysema

Herpes– brain tumors

Retroviruses– HIV, cancer, Gaucher disease

Sites for Gene Therapy

May be applied directly to tissue affected, or into cells that can produce a needed protein and divide, such as stem cells and progenitor cells, because they divide well and can travel fast, and change the fate of daughter cells

OR

These may be targeted….

Gene Therapy Sites

Endothelium: genetically altered endothelium can secrete a needed protein directly into the bloodstream

Skin: A skin graft can be genetically modified to secrete therapeutic proteins

Muscles: in Duchenne muscular dystrophy (DMD), the dystrophin gene can be cut smaller to deliver to cells so the muscles can function normally

Liver: delivering the gene that encodes for the LDL receptor, so more LDL can be produced to treat familial hypercholesterolemia (FH)

Lungs: several aerosols can be used to treat cystic fibrosis by replacing the defective gene. In AAT deficiency, levels of the enzyme elastase destroy lung tissue; Increasing the amount of the AAT enzyme will help prevent this.

Nerve tissue: fibroblasts used to secrete nerve growth factors or make enzymes that produce neurotransmitters

Cancer: ½ of all gene therapies target cancer. Suicide gene therapy may be used, as the vector or gene is introduced which kills the cells. Also, vaccines can be used to mark tumor cells so the immune system can recognize them easier

Suicide Gene Therapy

Sickle Cell Disease

Sickle cell disease is perhaps the most studied/researched inheritable disease

Could “turning on” fetal hemoglobin cure sickle cell by replacing the mutant beta chains (sickle BC’s) with normal gamma globin chains (fetal hemoglobin)?

In adults, the gamma genes are normally silenced with methyl groups. A drug called “hydroxyurea” can remove these groups, exposing the gamme genes. With the increase of gamma globin molecules in the bloodstream, these bind to the mutant beta globins, which prevents some cells to take on sickle shape. This prolongs the time it takes for the beta chains to join, and RBC’s are allowed to get into the lungs. Once cells pick up oxygen, sickling can no longer occur.

Hydroxyurea’s Effect

Gradual Success, but worth the wait

Soon, gene therapy will be applied to all common disorders, not only rare diseases

Because of success in the 1980s, huge expectations were held for the 90s….however, the progress has become painstakingly slow

Not every treatment is a 100% cure; some is only minimal physically Discoveries in the genome have revealed complexities that have yet to

be worked around Discovery of RNA inheritance may complicate gene therapy Somatic vs. Germline Although minimal, there IS success The right vectors MUST be found for further progress

Works Cited

McGleenan, Tony. Human Gene Therapy and Slippery Slope Arguments. Journal of Medical Ethics 21(6): 350-355,

December 1995. Lysaught, M. Therese. Gene "Therapy": A Test Case for Research With Children. Genetics and Ethics: An Interdisciplinary Study, 6th ed. St. Louis, Missouri: Saint Louis

University Press, 2004, pp. 216-252. Zohar, Noam J. “Prospects for ‘Genetic Therapy’ -- Can a Person Benefit from Being Altered?”. Bioethics 5(4): 275-288,

October 1991.