Genetics 12T:12TH - Huwe PDF

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Genetics Exam 3 Week 12T/12TH GENETIC COUNSELING  Addresses medical, psychological, sociological and ethical issues  Genetic counselor – health care professional w/ Master’s degree who helps patients and their families navigate the confusing path of genetic testing  Genetic counseling began in pediatrics, and prenatal care, and has become specialized  The field has even infiltrated public policy as genetic testing has become widespread  Help to understand results and options going forward GENETIC COUNSELORS  The US has about 3,000  Provide information to individuals, couples expecting children, and families about o Modes of inheritance o Disease risks and symptoms o Available tests and treatments  Interpret direct-to-consumer genetic tests and assist other health care professionals w/ genetic information in their practices  When genetic counseling began, it was “nondirective” o The practitioner did not offer an opinion or suggest a course of action, but presented options o A more recent definition of the role of the genetic counselor is “shared deliberation and decision making between the counselor and client”  Make pedigree w/ inheritance of disease and find the likelihood it’s inherited by chance  Help doctors decide best course of action THE GENETIC COUNSELING PROCESS  Reasons to seek genetic counseling o Family history of abnormal chromosomes o Elevated risk of single-gene disorder o Family history of multifactorial disorder o Family history of cancer  Genetic counseling sessions o Family history o Pedigree construction o Information provided on specific disorders, modes of inheritance, tests to identify at-risk family members o Links to support groups, appropriate services o Follow up contact GENETIC TESTING  Genetic tests are administered at all stages of human existence, and for a variety of reasons  Identifying mutations can help in diagnosis and choosing treatments  As the pace of exome and genome sequencing accelerates, and such testing becomes widely available  Microarrays – not full genome sequencing, looking for specific polymorphisms

VUS – variant of unknown significance Might find a deleterious mutation, but do not know the penetrance, need to consider this Stopped including data about breast cancer mutations in these commercial tests b/c people got double mastectomy for benign mutations o Looking for small deletions/duplications etc  Sperm selection – only done when there is a mutation in one of the chromosomes o Sperm w/ X chromosome weigh more than Y chromosomes o Will not do it for designer babies NEWBORN SCREENING  Usually tests for inborn errors of metabolism  Are not genetic tests, but instead they use tandem mass spectrometry to identify unusual metabolites or chemical imbalances that indicate a certain disease.  The field of newborn screening began in 1962 with the Guthrie test for phenylketonuria (PKU) o It detects phenylalanine, which builds up in affected individuals o Can lead to mental retardation nand early childhood death w/o treatment  In 1963, a specialized diet became available  The diet is difficult to follow, but does prevent mental retardation  After diet’s success, genetic tests expanded  Some states perform DNA tests on newborns as well as biochemical tests GENETIC TESTING OF CHILDREN  Chromosomal microarray (CMA) tests detects very small deletions and duplications that are associated w/ o Autism, developmental delay, intellectual delay, behavioral problems, other phenotypes GENETIC TESTING OF ADULTS  Like children, adults take single-gene tests as part of diagnostic workups based on symptoms or other test results  Faster DNA sequencing has lowered the cost of carrier tests to the point that it may be more economical to test everyone for many diseases with one blood sample per person DIRECT-TO-CONSUMER GENETIC TESTING  Companies market DNA-based tests for traits, susceptibilities, and genetic diseases to the general public  The Clinical Laboratory Improvement Amendments (CLIA) control genetic testing o These are some regulations, but not sure how rigorous it is  DTC tests presented as information, not diagnoses, may not be regulated  Unawareness of incomplete penetrance is one complication of DTC genetic testing  Very little regulation b/c FDA does not directly determine what results can be provided to consumer or what tests can be done  If patient does not want information, should doctor know?  If insurance pays for genetic tests, should they have access to that information?  Lower rates of life insurance w/ genetic testing? MATCHING PATIENT TO DRUG  Full genome sequencing can be used to see how patients will respond to medications  A pharmacogenetic test detects a variant of a single gene that affects drug metabolism o Look at one gene to see how metabolism will be affected o Women w/ the HER2 + subtype of breast cancer responds to the drug trastuzumab (Herceptin) o Patients w/ particular variants of CYP2C9 and VKORC1 require lower doses of warfarin  Warfarin – blood thinner  Mutations in these genes means you are more susceptible to Warfarin, may need to give lower dosages b/c a little bit goes a long way  A pharmacogenomic test detects variants of multiple gene or gene expression patterns that affect drug metabolism o Use of a DNA microarray depicting the expression of 18 genes to predict whether a person is likely to respond to certain drugs to treat hepatitis C, which have severe side effects o Look at multiple genes to see how metabolism will be affected TREATING GENETIC DISEASE  Treatments have evolved through stages  Removing an affected body part o o o

Replacing an affected body part or biochemical w/ material from donor Delivering pure, human proteins derived from recombinant DNA technology to compensate for the effects of a mutation o Give insulin (replace missing protein)  Refolding correctly a misfolded protein  Gene therapy, to replace mutant alleles, a recent innovation  Treat the symptoms w/ anti-inflammatory to lower the temperature TREATING THE PHENOTYPE  Lysosomal storage diseases are a subclass of inborn errors of metabolism  Issues w/ breakdown of glycolipids if untreated o Do not produce enough enzyme o Unfolded enzyme o Substrate builds up and product is deficient  Treatments are based on understanding metabolic pathways o If an enzyme is deficient or its activity blocked, the substrate builds up and the product is deficient  There are 3 general approaches for counteracting these diseases TYPE 1 GAUCHER DISEASE (most common lysosomal storage disease)  The enzyme glucocerebrosidase is deficient or absent  As the substrate (Glucocerebroside) builds up b/c there is little or no enzyme to break it down, lysosomes swell, ultimately bursting cells o Glucocerebroside = glucose attached to ceramide group, body cannot break it down  Symptoms include an enlarged liver and spleen, bone pain, and deficiencies in blood cells  Too few red blood cells cause the fatigue of anemia; too few platelets cause easy bruising and bleeding; and too few white blood cells increase the risk of infection. COUNTERACTING A METABOLIC ABNORMALITY  If enzymes broken, build up substrates and have lower product  Solution: Modify diet to reduce substrate LYSOSOMAL STORAGE DISEASE TREATMENTS  Enzyme replacement Therapy o Recombinant human enzymes infused to compensate for deficient or absent enzyme o Inject into infected individual and decrease amount of substrate that builds up o Biologics - expensive treatments  Cost a lot b/c not as many people need it as insulin/harder to make  Substrate reduction o Oral drug that reduces level of substrate, so enzyme can function more effectively o Reduce substrate o Need to reduce amount of gangliosides o Give oral drug to reduce level of substrate o Binds it and causes it to be excreted - not an enzyme  Pharmacological chaperone therapy o Oral drug that binds to patient’s misfolded protein, restoring function o Pharmaceutical chaperon o Refold enzyme into the correct orientation (have fxn again) o Normally for specific misfolds GENE THERAPY  Delivers working copies of genes to specific cell types or body parts, typically aboard modified viruses o Deliver new genes that codes for new proteins that restores the fxn  The first efforts focused on inherited disorders with a known mechanism, even though the conditions are rare  Targeting more common illnesses, such as heart disease and cancers  Germline gene therapy o Gamete or zygote alteration; heritable; not done in humans; creates transgenic organisms o All cells in body will be affected, all children will also be affected  Somatic gene therapy o Corrects only the cells that a disease affects; not heritable  

o Does not affect germline cells, offspring could still inherit disease GENE THERAPY CONCERNS Scientific  Which cells should be treated and how?  What proportion of the targeted cell population must be corrected to alleviate or halt progression of symptoms?  Is overexpression of the therapeutic gene dangerous?  Is it dangerous if the altered gene enters cells other than the intended ones?  How long will the affected cells function?  Will the immune system attach introduced or altered cells?  Is the targeted DNA sequence in more than one gene? Ethical  Does the participant in a gene therapy trial truly understand the risks?  If a gene therapy is effective, how will recipients be selected, assuming it is expensive at first?  Should rare or more common disorders be the focus of gene therapy research and clinical trials?  What effect should deaths among volunteers have on research efforts?  Should clinical trials be halted if the delivered gene enters the germline?  Playing God – designer babies, very expensive  Bad alleles passed on more often  Multifactorial genes could play different roles if scientists mess w/ them REQUIREMENTS FOR APPROVAL OF CLINICAL TRIALS FOR GENE THERAPY  Knowledge of the defect, how it causes symptoms, and the course of the illness (natural history)  An animal model and/or cultured human cells  No alternate therapies or patients for whom existing therapies are not possible or have not worked o If therapies could be curative it would work, if current therapy is not curative  Experiments as safe as possible INVASIVENESS OF GENE THERAPY  Ex vivo gene therapy – Is applied to cells outside of body that are then returned o CART 19 therapy o Remove cells – do gene therapy on those cells and put them back into individual o First type that was done o Often done on bone marrow cells (hemolytic disorder), immunodeficiency or hemophilia  In vivo gene therapy – is applied directly to an interior body part o Leber’s congenital amaurosis II therapy o The most invasive o Inject into individuals themselves, need to use a virus SOMATIC GENE THERAPY TARGETS  Endothelium – Can secrete needed proteins directly into bloodstream o The tie-like endothelium that forms capillaries can be genetically altered to secrete proteins into the circulation  Muscle – Accessible, comprises ½ body mass and has a good blood supply o Immature muscle cells (myoblasts) given healthy dystrophin genes may treat muscular dystrophy  Liver – Many functions and can regenerate o To treat certain inborn errors of metabolism, only 5% of the liver’s 10 trillion cells need to be genetically altered  Lungs – Are easily accessed w/ aerosol spray o Gene therapy can reach damaged lungs through an aerosol spray. Enough cells would have to be reached to treat hereditary emphysema or cystic fibrosis  Some areas are easier to reach than others GENE THERAPY: ADENOSIEN DEAMINASE DEFICIENCY (ADA)  Severe combined immune deficiency (SCID) can be caused by ADA deficiency o SCID can also be caused by other things o Need to live in isolated environment (bubble boy)

Toxins destroy T cells, thereby causing susceptibility to infections and cancer  Replacement of ADA in individuals genetically deficient was attempted  Cause deoxy ATP to build up b/c ADA enzyme deficiency  First gene therapy, took WBC and bone marrow cells and add ADA gene to them and insert cells back into body so products can be excreted as uric acid FIRST GENE THERAPY PATIENT  Ashanthi DeSilva – September 14, 1990  Ashanthi is doing well after she was part of a clinical trial of gene therapy that patched her own white blood cells w/ functional ADA genes.  By 2005, thirty youngsters had been treated, successfully, with a new version of the gene therapy  Worked very well GENE THERAPY: ORNITHINE TRANSCARBAMYLASE (OTC)  Deficiency of OTC is inherited as an X-linked recessive mutation  OTC normally breaks down amino acids present in protein  Lack of OTC allows buildup of ammonia, which damages brain function (mental deterioration (coma) and death  Usual Treatment: Low-protein diets and ammonia-binding drugs are used to treat OTC deficiency  Clinical trials to treat OTC deficiency were established using adenovirus as a vector for the normal OTC gene  Jesse Gelsinger had a mild OTC deficiency, volunteered for the OTC gene therapy trial and was accepted o Germline mosaic for disease, acquired mutation in blastocyst, therefore did not die in childhood like most people w/ this disease  Four days after gene therapy Jesse died from an overwhelming immune reaction and associated complications o Died b/c of immune rxn to virus, even though use virus that shouldn’t hurt you, put patients on immune suppressants  Other cases to halt gene therapy o Virus inserted genetic material in regulatory region (proto-oncogene) of genome, caused cancer in some patients o Mutated proto-oncogene to oncogene o Can now check to see where gene inserted b/c add section to cells they can find again GENE THERAPY: LEBER’S CONGENITAL AMAUROSIS II  Most severe form of blindness  Inherited as autosomal recessive disease  Mutation is in a gene called RPE65  Gene therapy first tried on breed of sheepdog that has the same mutation as humans  It was tried on 4 young adults, and later on 8 year old Corey Hass

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Video 1: New Hope for Gene Therapy: A Young Boys' Fight against Blindness (3:33)  Childhood form or retinitis pigmentosa

 Retina is not working correctly (back of the eye)  Upenn clinical trial  Eyes dilated, therapeutic virus delivered (carry gene that Corey is missing), restoration of

blockade, able to see Video 2: Jean Bennett on gene therapy as a treatment for blindness | Charlie Rose (showed 2 min)  Mutations in the RPE65 gene o These gene therapy is effective for these people Leber’s Congenital Amaurosis II  Affect rod cells, leads to blindness in early life  Inject viral vector into eye  Eyes are immunopriveleged, not the same immune rxn  Virus lacks ability to replicate  Inject into rod cells CART-19 THERAPY  The Emily Whitehead story

Video 1: Emily Whitehead First Child Treated in Trial of T Cell Therapy for Acute Lymphoblastic Leukemia (6:44)  Children's Hospital of Philadelphia  CART 19 (CTL019) treatment - advanced leukemia  B Cell ALL o For some children, chemotherapy does not work (treatment resistant) o Take T cells from pt, engineer cells to go after cancer cells and kill them o Increase in proteins (IL10) that control immune rxn, make Emily Whitehead ill o Gave her a drug to drop the levels of that protein  Arthritis medicine that targets IL10 o Complete remission Video 2: Emily’s Story: A Young Girl Beats Cancer w/ Immunotherapy  16 months of chemotherapy, relapsed (did not work)  Killer T cells  Ventilator for 2 weeks  T cells were actually working...