Genetic Screening

Leona Al-Sayah

National Institutes of Health

Background Information Genetic screening is a process to analyze DNA, and serves as

an important tool of modern preventive medicine.

The purpose is to identify persons whose genotype places them or their offspring at risk. Such screening has the potential to lessen the devastating impact of genetic disease.

The human race carries 3,000 - 4,000 diseases in its genes. The faulty gene that causes any of these diseases will be a one in 100,000 and 200,000 healthy gene in each cell.

In order to locate this faulty gene, scientists search for variations in larger pieces of DNA called markers. They are found nearby the DNA and become the basis of genetic screening. With such markers it becomes theoretically possible to screen individuals of every age, from infants to adults, even babies before birth.

History Although much has been discovered in recent decades to improve genetic testing, the history of genetics is ratheran old science and has been studied for many years. Between 1879 and 1882 Walter Fleming discovered chromosomes or DNA which is the subject of study in genetics and so began the history of real genetic testing.In 1902 inherited diseases were first linked to chromosomes and following this a number of other genetic disorders were found and described by various geneticists.In 1975, a method to isolate and analyze DNA fragments was discovered which is now known as the "Southern blot analysis" and it is urrently used in genetic testing.In 1983 the PCR method of DNA analysis was discovered and is now a popular method of DNA analysis in genetic testing. Today genetic testing is becoming more and more popular and the history of genetic testing has laid the foundation for modern analysis into diseases as well as paternity and ancestry DNA testing.

Uses To determine sex

To check for abnormal chromosome number

To check for early onset conditions (sickle cell, cystic

fibrosis)

To check for late onset conditions (Huntington’s disease,

Polycystic kidney disease)

To find susceptibility to diseases (hypercholesterol,

alcoholism)

To determine carriers of recessive genes (sickle cell, cystic

fibrosis)

ScreeningThere are two classes of genetic screening: Presymptomatic screening - this is used to test individuals whose health is in danger Carrier screening - carried out in healthy individuals where genes are harmful to the health of their future offspring. Other types of genetic screening usually include parental screening, newborn screening, forensic screening and susceptibility screening.

Once a person decides to proceed with genetic testing, a medical geneticist, primary care doctor, specialist, or nurse practitioner can order the test. Genetic testing is often done as part of a genetic consultation.

Genetic testing uses a sample of DNA-containing material like blood, saliva and amniotic fluid to search for variations in chromosomes genes and proteins. There are many different procedures used in genetic testing and many different reasons for their use. The screening of a particular disorder is carried out on one of the following samples: blood, bone marrow, amniotic fluid, hair, semen, skin.

A procedure called a buccal smear uses a small brush or cotton swab to collect a sample of cells from the inside surface of the cheek. The sample is sent to a laboratory where technicians look for specific changes in chromosomes, DNA, or proteins, depending on the suspected disorder. The laboratory reports the test results in writing to a person’s doctor or genetic counselor.

Procedure

DNA Amplification

Genetic testing can be done on very small samples. However, when more DNA is required for testing than is available, it can be amplified through processes like polymerase chain reaction, which copies a DNA molecule by stimulating the DNA-reproduction process.

Karyotyping

Conditions such as Down's and Turner's syndromes, which are caused by the inheritance of an extra or too few chromosomes can be revealed through karyotyping, which creates an image of the chromosomes found in an individual's somatic cells. This is one of the simplest forms of genetic testing as no molecular study is necessary.

Molecular Study

Genetically linked conditions have a standard form for healthy, sick or at-risk individuals. Genetic testing can isolate deletions or mutations of a gene or protein and either confirm a diagnosis or alert to the risk of developing a condition such as Huntington's chorea years or even decades before symptoms develop.

Newborn Screening Newborn screening is concerned with

the analysis of blood or tissue samples taken in early infancy in order to detect genetic diseases for which early intervention can avert serious health problems or death. This started in 1960 with the ability to test newborns for a rare metabolic disease, phenylketonuria (PKU). Two other examples of newborn screening are the testing of African - American infants for sickle cell anemia and Ashkenazic Jews for Tay-Sachs disease.

Newborn screening tests are done on a small blood sample, which is taken by pricking the baby’s heel. Unlike other types of genetic testing, a parent will usually only receive the result if it is positive. If the test result is positive, additional testing is needed to determine whether the baby has a genetic disorder.

Positive Viewpoint Genetic testing has potential benefits whether the

results are positive or negative for a gene mutation. Test results can provide a sense of relief from uncertainty and help people make informed decisions about managing their health care.

A negative result can eliminate the need for unnecessary checkups and screening tests in some cases. A positive result can direct a person toward available prevention, monitoring, and treatment options.

Some test results can also help people make decisions about having children.

Newborn screening can identify genetic disorders early in life so treatment can be started as early as possible.

Progress Markers have already been found for various diseases

such as Huntington's disease, cystic fibrosis, Duchenne's muscular dystrophy, hemophilia and thalassaemia, and some rare cancers. Scientists are also searching for the genetic connection with more common disorders where environment may play a role - Alzheimer's disease, diabetes, epilepsy, certain cancers and heart disease.

The term testing is usually used when seeking to identify individuals or those within a family, screening for analyzing samples from a larger group of people, perhaps within a population.

However, both these terms are often used to describe the same thing as the process and intent is the same: to discover if someone has disease or is a healthy carrier.

Diseases Found by Screening

Source: Office of Technology Assessment

Negative Viewpoint Genetic discrimination: People with genetic flaws, not all of which show up as dysfunctions, may be denied life insurance, health insurance, and access to schooling or to jobs.

Differential treatment: Employers could hire only those people whose genes indicate they are resistant to the health hazards of the work place, which is a cheaper alternative to making the work place safe for all.

Eugenics: Social or political pressure may be applied to people to make childbearing decisions on the basis of genetic information. Mating between those with valued genes may be encouraged while mating between two people with dangerous recessive traits may be prohibited. Women carrying fetuses with genetic abnormalities may be encouraged to abort.

Genetic determinism: Genetic determinism is the belief that behavioral and personality characteristics, such as intelligence or criminal behavior, are mostly a function of genes. Genetic determinism implies a fatalistic attitude toward health and disease. It can be used to justify bigotry and to perpetuate racial or ethnic inequalities. A genetic underclass could be created. Drastic procedures may be taken that may not have been necessary

Issues Even those diagnosed with

the present tests might be told they carry a debilitating mutation when they may never get sick in their lifetime. With each new test that detects a new mutation there will be a higher risk of misdiagnoses, and since there are now at least 360 known mutations that result in cystic fibrosis, population screening would be a costly and time-consuming process that would not achieve the intended results.

Genetic Discrimination Genetic discrimination occurs when people are treated differently by their employer or insurance company because they have a gene mutation that causes or increases the risk of an inherited disorder. People who undergo genetic testing may be at risk for genetic discrimination.

The results of a genetic test are normally included in a person’s medical records. When a person applies for life, disability, or health insurance, the insurance company may ask to look at these records before making a decision about coverage. An employer may also have the right to look at an employee’s medical records. As a result, genetic test results could affect a person’s insurance coverage or employment. People making decisions about genetic testing should be aware that when test results are placed in their medical records, the results might not be kept private.

Fear of discrimination is a common concern among people considering genetic testing. Several laws at the federal and state levels help protect people against genetic discrimination; however, genetic testing is a fast-growing field and these laws don’t cover every situation.

CostGenetic tests may be expensive because they are somewhat rare and labor intensive, undergo multiple levels of review, and may include any cost for blood draw or specimen collection, shipping costs, and genetic counseling or physician fees. These costs may vary depending on the type of test and who orders it.

Costs for Selected Genetic Tests by Disorder and Type of Test

LAB Test Sequencing AnalysisDenaturing gradient gel

electrophoresis

Allele Specific olligonucleotide

Protein truncation test

HNPCC $500-3000 $260 $250-800 - -

FAP $800-1000 - - $350-450 $235

BRCA1 $1290 - - $350-450 -

BRCA2 $1290 - - $190-354 -

BRCA- Ashkenazi mutations

- - - - -

Legal Matters With regard to genetic testing and information in general,

legislation in the United States called the Genetic Information Nondiscrimination Act prohibits group health plans and health insurers from denying coverage to a healthy individual or charging that person higher premiums based solely on a genetic predisposition to developing a disease in the future.

The legislation also bars employers from using individuals’ genetic information when making hiring, firing, job placement, or promotion decisions

The legislation, the first of its kind in the U.S. was passed by the United States Senate on April 24, 2008, on a vote of 95-0, and was signed into law by President George W. Bush on May 21, 2008. It went into effect on November 21, 2009.

Opinion Genetic testing has many benefits that may save a person and his or her family from troubles and ease their pains. Newborn screening may be used to avoid the medical and emotional hardships that accompany deadly disorders such as Tay-Sachs and cystic fibrosis that have onsets early in a child's life.

The fact that there is a probability of the disease occurring also raises problems and concerns, for some people may take extreme measures to prevent the disease from occurring as they have seen family members struggle. Such as in the case of a woman who got a mastectomy after a screening that showed she was susceptible to breast cancer to avoid getting it like her sister who died from it.

It is wonderful that deadly diseases can be avoided in some cases using this new technology, but it definitely has the potential to be misused. Therefore, genetic testing and screening must be used sparingly and at all costs avoid becoming a commercial service that can be exploited. Regulations to protect the wellbeing and identity of those tested must be enforced.

Works Cited http://www.ndsu.edu/pubweb/~··mcclean/plsc431/students99/

karthikeyan.htm

http://www.woodrow.org/teachers/bi/1992/gen_screen1.html

http://www.usatoday.com/news/health/2010-02-17-genetic-testing_N.htm

www.dnapolicy.org/resources/AlphabetizedDTCGeneticTestingCompanies.pdf

http://www.kaisernetwork.org/daily_reports/rep_index.cfm?DR_ID=52305

http://www.ehow.com/how-does_4927560_how-genetic-testing-done.html

http://find.galegroup.com/ovrc/retrieve.do?subjectParam=Locale%2528enBscreening%2524&contentSet=GSRC&sort=Relevance&tabID=T010&sg

http://learn.genetics.utah.edu/content/health/ngs/

http://www.scienceprogress.org/2008/05/a-brief-history-of-genetic-testing

http://www.genetichealth.com/genetic_testing_costs_of_genetic_testing.shtml