40-08: The Techniques of Medical Genetics

Hereditary disorders affect multiple organ systems and people of all ages. Many disorders are chronic ones, although acute crises often occur. The concerns of patients and families span a wide range of medical, psychological, social, and economic issues. These characteristics emphasize the need for clinicians to provide medical genetics services for their patients. This section reviews the laboratory and consultative services available from clinical geneticists and the indications for their use.

FAMILY HISTORY & PEDIGREE ANALYSIS

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.