The first step in considering how important genetic factors might be in the clinical situation of a patient is obtaining a detailed family history. At a minimum, a patient should be queried in detail about all first-degree relatives—parents, siblings, and offspring—(age, sex, health status if alive, including major illnesses; cause of death) and more distant relatives with reference to the particular condition at issue. Ethnicity of both sides of the family should be noted; any disorders known to be especially prevalent in a particular ethnic group should be asked about specifically. Once the family history is obtained, it should be analyzed; medical geneticists and genetic counselors are trained in this task and are particularly valuable when the busy clinician has neither the time nor the staff to pursue the information. A pedigree diagram (eg, eFigure 40–3) with the symbols filled in to indicate the presence of a condition can be instructive in suggesting a mode of inheritance. Once targeted genetic testing of the proband produces a result, the diagram also proves useful in identifying relatives who might benefit from counseling about similar testing.
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