Genetic testing

This section presents information on the benefits, costs, risks, and limitations of genetic testing. 

Genetic testing is voluntary. Because testing has both benefits and limitations, the decision about whether to be tested is a personal and complex one. A genetic counselor can help by providing information about the pros and cons of the test and discussing the social and emotional aspects of testing. 

Genetic testing can provide information about a person s genes and chromosomes. Available types of testing include  

Newborn screening is used just after birth to identify genetic disorders that can be treated early in life. Millions of babies are tested each year in the United States. All states currently test infants for phenylketonuria (a genetic disorder that causes mental retardation if left untreated) and congenital hypothyroidism (a disorder of the thyroid gland). Most states also test for other genetic disorders. 

Forensic testing uses DNA sequences to identify an individual for legal purposes. Unlike the tests described above, forensic testing is not used to detect gene mutations associated with disease. This type of testing can identify crime or catastrophe victims, rule out or implicate a crime suspect, or establish biological relationships between people (for example, paternity). 

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

Genetic tests are performed on a sample of blood, hair, skin, amniotic fluid (the fluid that surrounds a fetus during pregnancy), or other tissue. For example, 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. 

The pattern of inheritance one finds in a family depends on whether the mutant gene is located on an autosome, the X chromosome, or mitochondrial DNA. It also depends on whether the mutant gene is dominant or recessive. 

Autosomal dominant diseases are more likely to show late onset of symptoms. The genes involved often encode noncatalytic proteins, and may occasionally show incomplete penetrance or variable expression in a pedigree. 

Solid Lines Represent Bands Reactive With Probe 

Only the Bands Reactive With Probes Are Made Visible 

The firagments in the material to be analyzed (DNA, RNA, or protein) are separated by gel electrophoresis. The smaller molecules travel faster and appear nearer the bottom of the gd. The bands of material in the gel are transferred or blotted to the surface of a membrane. The membrane is incubated with a (usually radioactive) labeled probe that will specifically bind to the molecules of interest. Visualization of the labded probe (usually by autoradiography) will reveal which band interacted with the probe. The most common types of blots are compared in Table 1-7-1. Most typically, DNA restriction fragments are analyzed on a Southern blot. 

---

Diagnosis of CF is based on two separate elevated sweat chloride concentrations of greater than or equal to 60 mEq/L (or mmol/L) obtained through pilocarpine iontophoresis (referred to as the sweat test ). Genetic testing (CFTR mutation analysis) may be performed to confirm the diagnosis, screen in utero, or detect carrier status. More than 70% of diagnoses are made by 12 months of age and almost all are made by age 12. 

Yan H, Kinzler KW, Vogelstein B. Tech.sight. Genetic testing - present and future. Science 2000 289 1890-1892. 

Ross LF, Moon MR. Ethical issues in genetic testing of children. Arch Pediatr Adolesc Med 2000 154 873-879. 

A Drousiotou, O Ioannou, T Georgiou, E Mavrikiou, G Christopoulos, T Kyria-kides, M Voyasianos, A Argyriou, L Middleton. Genet Test 2 55-60, 1998. 

Genetic tests are being prospectively validated as decision-support tools for adjuvant chemotherapy in node-negative patients to identify characteristics of the primary tumor that may predict for the likelihood of metastases and death. 

B. How likely would you be to participate in genetic research if it involved researchers reviewing your medical records in addition to a genetic test in order to explore possible links between genetic test results and health history ... 

A. If your employer could get the results of a genetic test that showed whether you were more likely to get sick in the future, what impact, if any, would this have on your willingness to take the test ... 

FIGURE 1.9. Percentage Willing to Undergo Genetic Testing if Results Were Available to Employers, Health Insurers, and Life Insurers (by race/ethnicity). 

FIGURE 1.10. Percentage Willing to Undergo Genetic Testing (by education). 

In the multivariate analysis, African Americans were nearly twice as likely as whites (OR = 1.88, p = 0.013), whereas Asians were 2.6 times (p = 0.001) and Hispanics 3.1 times (p < 0.001) as likely as whites to have such a test. These results suggest that confidentiality of genetic test results and possible discrimination by employers is not a salient concern of racial/ethnic minorities, but it is a concern among whites. 

The final question in this section of the interview inquired into the respondents willingness to have a genetic test if the results were available to their life insurance company. Again, the likelihood of participation decreases with years of education and is significantly higher among racial/ ethnic minorities compared with whites. What is noteworthy here is the finding that respondents who have total family incomes above 50,000 are... 

---