Pedigree analysis Health Article

Definition

A pedigree is a family tree or chart made of symbols and lines that represent a patient's genetic family history. The pedigree is a visual tool for documenting biological relationships in families and the presence of diseases. Pedigree analysis is an assessment made by a medical professional about genetic risk in a family.

Purpose

Pedigrees are most often constructed by medical geneticists or genetic counselors. People are referred to genetic professionals because of concern about the presence of a genetic condition in a family member. Pedigree analysis can help identify a genetic condition running through a family, aids in making a diagnosis, and aids in determining who in the family is at risk for genetic conditions. During pedigree construction, the family's beliefs about the cause for a genetic disease or emotional issues related to a diagnosis may be revealed. For instance, family members may experience guilt or shame about passing on a genetic trait. Thus, the communication process involved in taking the family history may allow the health care provider to identify areas in which the patient may need reassurance, education, or emotional support.

Pedigree symbols

A standard set of symbols has been established for use in creating pedigrees. Some of the most commonly used symbols are shown in this entry. When a person is affected with a birth disorder, mental retardation, or other health problems, the individual is shaded or marked. If more than one condition is present in a family, different identifying marks should be made. A key to decipher these markings should also be included on the pedigree. The meaning of each horizontal and vertical line is also shown.

Information obtained

A typical pedigree is made of information about three generations of a family. The consultand is the person seeking genetic evaluation, counseling, or testing. The proband in a family is the person in a family affected with a genetic disorder. Beginning with the consultand, questions should be asked about the health of first, second, and third degree relatives. First-degree relatives are children, parents, and siblings. Second-degree relatives are half siblings, nieces, nephews, aunts and uncles, grandparents, and grandchildren. Third-degree relatives are first cousins. Important information to obtain on both sides of the family includes:

• ages or dates of birth
• presence of any birth disorders, learning problems, chronic illnesses, surgeries, or medical treatments
• presence of specific features of a disease if the condition is suspected in the family
• genetic testing results if previously performed in the family
• cause of death for deceased family members
• pregnancy losses, stillbirths, or infant deaths and causes
• infertility in the family
• ethnic background of the families
• consanguinity

It is important to establish the accuracy of information given by patients. Therefore, medical records are often requested in order to provide accurate risk assessment.