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The Family Tree (Pedigree)

Genetic counseling, and effective treatment of genetic disorders, depends in part on the availability of a family history, or pedigree. The family history can shed light on and offer clues about disease or allow predictions about potential disease. In some ways, the pedigree is a road map back into time that can help shed light on the future. Thus, discovering whether a patient is at risk for any genetic disorder requires knowing with great accuracy an individual’s health history and that of his or her family.

When used in medicine, the pedigree is a historical diagram that traces family genetic characteristics, health problems, and diseases.  Because charting a pedigree involves keeping track of many pieces of information, a diagram is made using symbols. The symbols distinguish males and females, show relationships among family members, and indicate relevant individual genetic traits. In genetic counseling, the family tree is used to:

  • Establish patterns of gene inheritance within a family
  • Allow for calculation of recurrence risks
  • Identify individuals at risk
  • Rule out certain diagnoses.

Properly diagrammed, the pedigree will provide helpful details about each individual in the family and how the extended family (grandparents, uncles, aunts, grandchildren, in-laws) fared health-wise over time. Details provided by the pedigree include:

  • Ages of relatives when they died
  • Causes of death
  • Details about pregnancy and birth (e.g. miscarriages, stillbirths, elective pregnancy terminations, birth defects, mental retardation)
  • Who in the family inherited a disorder and who did not
  • Types of illnesses and disease that are common among family members
  • Whether or not family members experienced any problems such as deafness, blindness, and mental or psychiatric problems.

Often, the counselor will suggest that you obtain some of this information before coming to the genetics clinic. This typically involves calling on certain relatives to ask them questions about the health of grandparents, spouses, siblings, sons, daughters, etc.

Before the process of charting the family history begins, the genetic counselor will explain the objective of the exercise and demonstrate the pedigree symbols and how they are used. Many persons worry that they will never be able to answer detailed questions about the members of their extended families. But there is no pressure involved, and the counselors are skilled at helping patients recall basic details. The family history usually takes about 15 to 20 minutes to obtain.

You will be asked direct questions about the health of your grandparents, parents, and brothers and sisters. If you have children, you will be asked about their health and that of their father. Examples of Questions Asked in Genetic Counseling:

  • “Does anyone in your family have a child with mental retardation or learning disabilities?”
  • “Has anyone in your family had cancer before age 40?”
  • “Has your child always had difficulties speaking or is this something new?”
  • “Was anyone in your family ever treated for mental illness?”

Because every relevant piece of information may be helpful for creation of the pedigree, the genetic counselor will ask you for basic information about any step – and half-relations, whether or not any family members have been adopted, whether any children were born outside of a reported marriage, and whether any family members are involved in consanguineous relationships (meaning that the partners are related by blood; for example, distant cousins who have married one another).

Reference: National Society of Genetic Counselors

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