Pedigree

Pedigrees are hand-drawn or created using special computer software. The standard pedigree typically includes at least three generations, with each generation Degrees of relationship shown within a simplified pedigree. The proband is the individual first coming to the attention of the geneticist. arranged horizontally and connected to the other generations by lines. Family members who have the genetic disorder in question are colored-in or shaded. Unique symbols represent carriers, miscarriages, people of unknown sex, twins, and other categories of individuals. Furthermore, different patterns within the pedigree symbol may represent variable expression (variation in symptoms of individuals with the same disorder). For example, in a pedigree showing myotonic dystrophy, a shaded upper-left quadrant of the male or female symbol may represent cataracts, but a shaded right-lower quadrant may represent heart problems.

The process of collecting the family history used to draw the pedigree includes interviewing the informant and asking questions in three general categories. The detailed information about family members is recorded under the symbol for that individual. First, the interviewer asks standard questions about the family members, resulting in a skeleton picture of the family. These questions collect identifying information about each family member, such as their names, names of their parents, siblings, and children, dates of birth, dates of death, cause of death, and pregnancies. Detailed information is also included about general health problems, such as cancer and heart disease, and their specific symptoms, onset, and age at diagnosis. The interviewer may also ask about the ethnic background of family members and any possible consanguineous relationships (relationships between individuals who are related to each other by blood, such as first cousins).

Second, the interviewer may ask general questions to identify common genetic syndromes in the family, such as birth defects, mental retardation, vision and hearing loss, and common genetic disorders found more prevalently in certain ethnic backgrounds. For example, cystic fibrosis is relatively more common in people of Western European decent, whereas sickle cell disease is more common in those of African decent. If any common genetic syndromes are identified, they are then discussed during the genetic counseling appointment.

Lastly, the interviewer may collect targeted information about the specific genetic disease for which the family was referred. Information is gathered on the symptoms of the disease, age of onset, and age at diagnosis. These targeted questions help genetic counselors and researchers identify the typical course of disease in the family, disease severity, possible variable expression, reduced penetrance, or genetic anticipation. Because accurate diagnoses are essential for accurate genetic counseling and research studies, all diagnoses should be confirmed by medical records. Further, pedigree updates can be obtained over time during follow-up genetic counseling sessions or research interviews.