Ch.13: Genetics

Education on Genetic Testing

100

What is a genetic counselor & what do they do?

• People considering genetic testing should meet with a genetics counselor who is specially trained in medical genetics and counseling.

• Counseling can help you understand the purpose of genetic testing, considerations before testing, and the emotional and medical impact of the test results.

• Genetics counseling can help you understand the pros and cons of genetic testing before deciding to undergo a genetic test.

200

What is the education associated with genetic testing?

• Genetic testing can be expensive. Your health insurance may not cover the cost.

• Genetic testing may determine whether you are predisposed to developing an inherited disease.

• A particular genetic test will only tell you whether there is a specific genetic variant or mutation. Positive tests do not mean you will develop that disease or disorder. Neither can the results tell you when you will develop the disease.

• If a genetic test shows a genetic predisposition to an inherited disorder, the news can be depressing.

• Knowledge of a genetic predisposition to a disease may motivate you to take preventive measures (e.g., taking drugs for familial hypercholesterolemia) or make lifestyle changes to lower the risk for a disease (e.g., exercising to decrease the risk for type 2 diabetes).

• If a genetic test reveals you are at risk for a specific genetic disorder, there is the chance that other family members may be at risk.

• If a genetic test reveals you are at risk for developing an inherited disease, whether you decide to share that information with family members is a personal and ethical decision that you will have to make.

• Genetic testing may provide important information that you can use when making decisions about having children.

Comparison of Genetic Disorders

100

Describe Autosomal Dominant Disorders

• Males and females are affected or have the disease equally

• More common than recessive disorders and usually less severe

• Affected persons show variable expression

• Affected persons may have an affected parent

• Children of a heterozygous (affected) parent have a 50% chance of being affected

• Affects persons in successive generations

• EX:

  • Breast and ovarian cancer related to BRCA genes

  • Familial hypercholesterolemia

  • Hereditary nonpolyposis colorectal cancer

  • Huntington disease

  • Neurofibromatosis

  • Marfan syndrome

200

Describe Autosomal Recessive Disorders

• Affects males and females equally

• Heterozygotes are carriers and usually asymptomatic

• Affected persons may have unaffected parents who are heterozygous for trait

• Children of 2 heterozygous parents have a 25% chance of being affected and a 50% chance of being carriers

• Often no family history of disease

• EX:

  • Cystic fibrosis

  • Phenylketonuria

  • Sickle cell disease

  • Tay-Sachs disease

  • Thalassemia

300

Describe X-Linked Recessive Disorders

• Most affected persons have unaffected parents

• Affected persons are usually male

• Daughters of affected males are carriers

• Sons of affected males are unaffected (unless mother is a carrier)

• EX:

  • Duchenne muscular dystrophy

  • Hemophilia

  • Wiskott-Aldrich syndrome

400

Describe Y-Linked Disorders

• Y- chromosome mutation

• Father transmits to sons (only men affected)

Risk Factors for Genetic Disorders

100

List Risk Factors

Tobacco use, smoking, radiation, family hx, alcohol use, diet, etc.