Family history: the three-generation pedigree.

The collection of a family history ranges from simply asking patients if family members have the same presenting illness to diagramming complex medical and psychosocial relationships as part of a family genogram. The three-generation pedigree provides a pictorial representation of diseases within a family and is the most efficient way to assess hereditary influences on disease. Two recent events have made family history assessment more important than ever: the completion of the Human Genome Project with resultant identification of the inherited causes of many diseases, and the establishment of national clinical practice guidelines based on systematic reviews of preventive interventions. The family history is useful in stratifying a patient's risk for rare single-gene disorders and more common diseases with multiple genetic and environmental contributions. Major organizations have endorsed using standardized symbols in pedigrees to identify inherited contributions to disease.