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Lowdermilk: Maternity & Womens Health Care, 10th Edition

Chapter 03: Clinical Genetics

Key Points - Print

This section discusses key points about genetics and genomics.

o Recent advances in molecular biology and genomics have revolutionized the field of

health care by providing the tools needed to determine the hereditary component ofmany diseases.

Genetics is the study of individual genes and their effect on relatively rare single-

gene disorders. Genes are the basic physical units of inheritance that are passed

from parents to their children and contain the information needed to specify traits.

Genomics is the study of all the genes in the human genome together, including

their interactions with each other and the influence of the environment and other

psychosocial and cultural factors. The genome is the entire set of genetic

instructions found in each cell.o Increasingly, nurses from all specialty areas and practice settings are expected to have

competencies in genetics and genomics. For nurses with expertise in these topics,

expanded roles are developing in maternity and womens health nursing.

o The Human Genome Project is the major force behind the genetics revolution. The

Project uncovered two key findings:

First, all humans are 99.9% identical at the deoxyribonucleic acid (or DNA)

level.

Second, about 20,500 genes are in the human genome.

o Most genetic tests offered in clinical practice are tests forsingle-gene disorders in

clients with symptoms or a family history of a genetic disease. Some genetic tests are

prenatal tests or tests used to identify the status of a fetus at risk for a genetic disorder.

o One clinical application of the Human Genome Project has been pharmacogenomic

testing, in which genetic information is used to guide a clients drug therapy.

o The decision to undergo genetic testing is often based on feelings of responsibility and

commitment to others. Otherfactors that may affect the decision include social norms,

location, socioeconomic status, and cultural and ethnic differences.

This section provides critical points about clinical genetics.

o Genes are the basic units of heredity responsible for all human characteristics. They

comprise 23 pairs of chromosomes: 22pairs of autosomes and 1pair of sex

chromosomes.

o Chromosomal abnormalities are a major cause of reproductive loss, congenital

problems, and gynecologic disorders. Abnormalities can occur in autosomes and sex

chromosomes.

o Autosomal abnormalities involve differences in the number or structure of chromosome

pairs 1 through 22. They result from unequal distribution of genetic material throughgamete formation. When a normal gamete unites with a gamete that has an extra

chromosome, the result is a trisomy.

Mosby items and derived items 2012, 2007, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.

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The most common trisomy is Down syndrome.

Other autosomal trisomies that maternity nurses may see are trisomy 18 (or

Edward syndrome) and trisomy 13 (or Patau syndrome).

o Several sex chromosome abnormalities result from nondisjunction during

gametogenesis.

The most common deviation in females is Turner syndrome, in which an Xchromosome is missing.

The most common deviation in males is Klinefelter syndrome, in which an extra

X chromosome is present.

o Most common congenital malformations result from multifactorial inheritance, which

is a combination of genetic and environmental factors. Examples include cleft lip, cleftpalate, congenital heart disease, neural tube defects, and pyloric stenosis.

o People acquire gene mutations that can lead to cancer in three main ways:

First is through the environment, such as when exposure to tobacco smoke leads

to lung cancer.

Second is by chance when normal metabolic processes lead to DNA damage.

Third is through inherited mutations from parents, which account for 5% to 10%

of all cancers.

o Cancer genetics is an important emerging field, especially in breast, ovarian, and colon

cancer.

o Advances in genetics have complex ethical, legal, and social implications. Through

genetic counseling, professionals provide genetic information, education, and support to

individuals and families with ongoing or potential genetic health concerns.