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To understand genetics we have to review some basic concepts, the history of their development and a glossary of terms: Genetics: Studies the human characteristics inherited from our parents. DNA: Desoxyribonucleic acid is a compound formed by a double chain of four amino acids, also called bases. The chains are helicoidal in shape thus their definition as a double helix with bridges among their elements. The four amino acids are Adenine, Guanine, Cytosine and Thymine. Each chromosome is a single long DNA molecule composed by these bases. There are three billion bases in a human being. The year 2003 celebrated the 50th anniversary of the DNA discovery by Watson and Crick in England, February of 1953, based on the pioneering work of Rosalind Franklin. This feat has been considered to be the opening of the secret of life and it is a landmark in the history of medicine. This
structure was proposed by James Watson and Francis Crick Chromosomes are packets of genes in the nucleus of cells. The human being has 23 pairs, total 46. One chromosome comes from the mother and another one from the father to make the pair, or diploid .Two of the 46 chromosomes are sex chromosomes called X and Y. Females have two X chromosomes while males have one X and one Y chromosome. Genes are contained in chromosomes and carry the information for making all the proteins required by all living organisms. They are about 20,000 genes responsible for a human being. They determined characteristics such as eye color and hair, height as well as some disorders passed from parents to children. Genome is the entire content of DNA in the body including all of its genes. The Human Genome Project begun in 1990 and by June of 2000, 85 % of its elements (DNA) have been drafted or roughly identified. Genotype and Phenotype: Genotype refers to the genetic constitution of an organism (the blue print), to be distinguished from its physical appearance or phenotype, the individual itself. Genomic is the study of
how genes interact and determine the characteristics of living things.
Genetic Disorders occur when DNA mutations or chromosomal defects are passed to the offspring. If only one pair of genes is affected, it causes a uni-factorial disease such as sickle cell anemia and cystic fibrosis. If many different genes are involved, combined with environmental factors, they cause multi-factorial diseases such as asthma, diabetes and cardiovascular disease. To summarize and better illustrate the concepts mentioned above, consider the genome as a book with 23 chapters made up by the chromosomes. These are in pairs or diploids, each half is a haploid. There are 23 diploids and 46 haploids. Each chapter has thousands of stories or genes totaling up to 30,000 in the human being. Each story or gene has thousands of paragraphs called exons. Each paragraph has many words or codons. Each codon has a number of letters called bases. So far the total number of bases has been calculated to be 3 billion, but only 3% form genes. Four bases: Adenine, Guanine, Cytosine and Thymine form a DNA molecule, chemically known as a nucleotide. “Over 80% of all deaths are caused by 20 diseases, associated with no more than 200 or 300 genes, all of which are about to be identified in the very near future.” (Dr. Robert Roberts, Molecular Cardiology September 2000) What is gene testing? How does it
work? Genetic tests are used for the following:
Screening Embryos for Disease: Pre-implantation genetic diagnosis (PGD) is a test that screens for genetic flaws among embryos used for in-vitro fertilization. With PGD testing DNA samples from embryos created in-vitro by the combination of a mother's egg and a father's sperm are analyzed for gene abnormalities that can cause disorders. Fertility specialists can use the results of this analysis to select only mutation-free embryos for implantation into the mother's uterus. Before PGD, couples at higher risks for conceiving a child with a particular disorder would have to initiate the pregnancy and then undergo chorionic villous sampling in the first trimester or amniocentesis in the second trimester to test the fetus for the presence of disease. If the fetus tested positive for the disorder, the couple would be faced with the dilemma of whether or not to terminate the pregnancy. With PGD, couples are much more likely to have healthy babies, Although PGD has been practiced for years, only a few specialized centers worldwide offer this procedure. In gene tests, scientists scan a patient's DNA sample for mutated sequences. A DNA sample can be obtained from any tissue, including blood. For some types of gene tests, researchers design short pieces of DNA called probes, whose sequences are complementary to the mutated sequences. These probes will seek their complement among the three billion base pairs of an individual's genome. If the mutated sequence is present in the patient's genome, the probe will bind to it and flag the mutation. Another type of DNA testing involves comparing the sequence of DNA bases in a patient's gene to a normal version of the gene. Cost of testing can range from hundreds to thousands of dollars, depending on the sizes of the genes and the numbers of mutations tested. What are some of the pros and cons of gene testing? Gene testing already has dramatically improved lives. Some tests are used to clarify a diagnosis and direct a physician toward appropriate treatments, while others allow families to avoid having children with devastating diseases or identify people at high risk for conditions that may be preventable. Aggressive monitoring for and removal of colon growths in those inheriting a gene for familial adenomatous polyposis, for example, has saved many lives. On the horizon is a gene test that will provide doctors with a simple diagnostic test for a common iron-storage disease, transforming it from a usually fatal condition to a treatable one. Commercialized gene tests for adult-onset disorders such as Alzheimer's disease and some cancers are the subject of most of the debate over gene testing. These tests are targeted to healthy pre-symptomatic people who are identified as being at high risk because of a strong family medical history for the disorder. The tests give only a probability for developing the disorder. One of the most serious limitations of these susceptibility tests is the difficulty in interpreting a positive result because some people who carry a disease-associated mutation never develop the disease. Scientists believe that these mutations may work together with other, unknown mutations or with environmental factors to cause disease. A limitation of all medical testing is the possibility for laboratory errors. These might be due to sample misidentification, contamination of the chemicals used for testing, or other factors. Many in the medical establishment feel that uncertainties surrounding test interpretation, the current lack of available medical options for these diseases, the tests' potential for provoking anxiety, and risks for discrimination and social stigmatization could outweigh the benefits of testing. For what diseases are gene tests available? Currently, more than 900 genetic tests are available from testing laboratories. Some gene tests available in the past few years from clinical genetics laboratories appear below. Test names and a description of the diseases or symptoms are in parentheses. Susceptibility tests, noted by an asterisk, provide only an estimated risk for developing the disorder. Contact Gene Tests for comprehensive information on test availability and genetic testing facilities. Currently Available DNA-Based Gene Tests:
Currently in the United States, no regulations are in place for evaluating the accuracy and reliability of genetic testing. Most genetic tests developed by laboratories are categorized as services, which the Food and Drug Administration (FDA) does not regulate. Only a few states have established some regulatory guidelines. This lack of government oversight is particularly troublesome in light of the fact that a handful of companies have started marketing test kits directly to the public. Some of these companies make dubious claims about how the kits not only test for disease but also serve as tools for customizing medicine, vitamins, and foods to each individual's genetic makeup. Another fear is that individuals who purchase such kits will not seek out genetic counseling to help them interpret results and make the best possible decisions regarding their personal welfare. More information on these questionable test kits is available from Dubious Genetic Testing, an online report provided by Quackwatch. For a brief overview of the current regulatory environment for genetic testing, see the Oversight of Genetic Testing, a Genetics Brief from the National Conference of State Legislatures. Does insurance cover genetic testing? In most cases, an individual will have to contact his or her insurance provider to see if genetic tests, which cost between $200 and $3000, are covered. Usually insurance companies do not cover genetic tests, those that do will have access to the results. Insured persons would need to decide whether they would want the insurance company to have this information. States have a patchwork of genetic-information nondiscrimination laws, none of them comprehensive. Existing state laws differ in coverage, protections afforded, and enforcement schemes. The National Conference of State Legislatures provides a listing of current legislation regarding genetic information and health insurance. The recent marketing of genetic test kits directly to consumers, may lead to an increase in demand for insurance coverage. See the Genetics and Health Insurance (PDF) policy brief from the National Conference of State Legislatures for more information. Secretary's Advisory Committee on Genetic Testing - Access documents about oversight of genetic testing, genetic discrimination legislation, gene patenting and searching, and secondary subjects. Promoting Safe and Effective Genetic Testing in the United States - Final report of the Task Force on Genetic Testing created by the National Institutes of Health-Department of Energy Working Group on Ethical, Legal, and Social Implications of Human Genome Research. Published September 1997 How will the knowledge of Genetics
influence medicine and specifically the management of cardiovascular
disease? Genetics offers the following contributions to medicine: Predictability: By having a genetic profile, individuals will be able to know their propensity to develop certain disorders before symptoms appear. Examples: many forms of cancer, premature heart attacks and strokes, arterial hypertension, diabetes. Recently a study in Vernata, Italy by Dr. Franco Romeo, identified a mutation of gene LOX-1 which promotes oxidized lipids (LDL) to accumulate in the lining of the coronary arteries leading to heart attacks. Determining carrier status: Important for prospective parents before having offspring. The parents may be free of overt illness themselves but may be carriers. When both parents are carriers, all of their offspring will be affected by a genetic disorder. Diagnosis: Diagnosing illnesses affecting families secondary to gene mutations, before the illness presents its full manifestations is clearly important. In newborns or even in the prenatal state by amniocentesis the diagnosis of certain conditions can accurately be made, for instance, phenylketonuria, cystic fibrosis, sickle cell anemia. Individual Identification (ID): Establishes true identity in questionable fatherhood, or for forensic purposes. It will replace regular finger printing. Gene manipulation and therapy: It can be done by transplanting defective genes with healthy genes, by modifying or administering genes that are lacking in certain conditions, and by removing certain genes that caused abnormalities or unwanted characteristics. Pharmacogenomics, molecular medicine and proteinomics: The Genome Human Project has opened enormous possibilities for the treatment of diseases. Miracle drugs or “designer drugs” are in the making. With the aid of ultra-fast computer-driven devices, droplets of genetic material are sampled and analyzed for a specific code. Dr. Francis Collins, Director of the Human Genome Research Institute of NIH (National Institute of Health) stated ”If you understand the genetic basis of a disease, then you can predict what protein it produces and set about developing a drug to block it”. Traditionally, physicians prescribe drugs treating diseases at the last phase of a very complex chain of biochemical events. In the near future, individual patients will be given medications designed specifically for them according to their pertinent code at their onset of their disease. Medications will be more effective; their dosage will be precisely prescribed. At the end, medical care will be more efficient and less expensive. Redundancy of multiple agents and their over-dosage will be avoided. The traditional “trial-and-error” method in the use of therapies will not longer occur. Side effects and allergic reactions will be precisely predicted in patients. Another development will be the precise targeting of affected organs and tissues for the most beneficial effect of medications. Proteinomics will determine the effective vectoring or transporting of drugs by using certain proteins and modified viruses sent to the intended targets in precise doses. At present, some drugs have to be administered in larger doses systemically in order to obtain high enough blood levels in the organs and tissues being treated. With the new advances in proteinomics the cost-effectiveness of medical therapy will be very beneficial. Stem cell therapy and cloning: Stem cells are primitive cells capable of regenerating tissues or organs when placed in areas of need. Stem cells are normally present in the human body, regardless of its age, usually in the bone marrow, peritoneum (membranes inside of the abdomen) and even in the brain. Injection of these cells in the heart muscle of patients suffering heart attacks has shown spectacular repairs. Dr. Perin, from the Texas Heart Institute reported great results in 21 patients suffering from congestive heart failure secondary to coronary disease. He injected multiple sites of the heart muscle with stem cells in the most affected areas (Reported in Circulation, April 2003). Cloning of human beings for the purpose of obtaining a bank of stem cells is being done, regardless of the ethical controversy. When the political and religious issues are settled, this method, properly legislated, will provide stem cells in amounts required by certain diseases, changing their otherwise tragic outcome. This is the case in spinal injuries, ALS (Amyotrophic lateral sclerosis) myocardiopathies (diseases of the heart muscle) and even strokes and other forms of brain damage. The following websites were used regarding
genetics and related illnesses. Genes,
Dreams, and Reality: The Promises and Risks of the New Genetics
- Article from Judicature. Updated 18th 2007 |
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Cardio Wellness, Inc. 2004 cardiowellness@comcast.net |
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