genetic factors that haven’t been defined. If positive, the woman should be informed about her 50% risk to transmit the mutation to each child. However, general consensus among the genetics community is that fetuses or minors should not be tested for genes that will cause problems later in life (presymptomatic diagnosis) unless there are clear benefits for prevention. Cancers are additional examples of multifactorial disorders like coronary artery disease that were discussed in the previous section. Most will confer low risks for family members unless the same cancer is present in multiple relatives or a given cancer has an unusual or extreme presentation (e.g., early onset, associated features). Single gene diseases can also be concealed amidst multifactorial cancers, exemplified by the BRCA genes or cancer syndromes like Li-Fraumeni (bone, breast, brain cancers— OMIM #151623) or Gardner disease (colon cancer-- OMIM #175100) that are due to single gene mutations. Alertness for early onset or recurrent types of cancers in families allows evaluation for a growing number of cancer genes or susceptibility markers. It is now thought that every cancer has specific gene or chromosome changes that guide prognosis and sometimes even therapy (e.g., the Gleevec antibody therapy designed to inhibit a tyrosine kinase produced from a specific chromosome translocation in chronic myelocytic leukemia-- OMIM #608232). DNA markers are even being found that predict response of individuals with a particular type of tumor to chemotherapy—one type of DNA marker may indicate likely toxicity while another indicates likely good response. This linkage of genetic information to drug response is generally referred to as pharmacogenomics, and is another trend that will benefit greatly from nursing involvement. RULE 12: Recognition of family histories with multiple affected individuals or those with unusual/extreme presentations of common diseases (e.g., heart attacks) allows definition of risk factors (e.g., cholesterol) and preventive management. 24
Problem set 1: Key genetic presentations Select the best single answer to the following questions: 1-2 1. A term female infant to a 37-year-old mother with three prior children has a low birth weight and a poor latch for breast-feeding the first 24 hours of life. Mother had first trimester maternal serum screening (quad screen) that was normal. Your assessment of the baby reveals an unusual facial appearance with a broad nose and extra skin folds on the neck. Based on the history, which of the following is the most likely reason for poor breast-feeding in this child: A. Maternal incompetence B. Autosomal dominant disorder in mother C. X-linked recessive disorder in child D. Chromosomal disorder in child E. Multifactorial disorder in child 2. Prior to receiving test results, the most important aspect of care along with evaluating the feeding problem is: A. Genetic counseling regarding recurrence risk B. Genetic counseling regarding prenatal diagnosis C. Supportive counseling for future mental retardation D. Supportive counseling for probable birth defects E.
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