A pedigree can be just as useful in determining that a condition is not genetic as in establishing that a condition is inherited in a family. This is particularly true for common complex health conditions such as mental illness, heart disease, and cancer. For example, Jean is a 42-year-old premenopausal woman with unilateral breast cancer. Her mother is healthy at age 65 years, but Jean's maternal grandmother, Pamela, died of breast cancer at age 63. This limited family history may raise your initial suspicion for a familial breast cancer. Yet when you take an extended family history, you find that Jean's mother has three healthy sisters between the ages of 68 and 72 years. You also find that Pamela had two sisters who were cancer free in their mid-70s when they died of heart disease. This "negative" family history is just as important as the "positive" family history of cancer in risk assessment and determining cancer screening protocols.
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