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Contents

Pedigrees

Chapter:
Nomenclature
Author(s):

Harriet S. Meyer

Pedigrees

Pedigree format recommendations are put forth by the Pedigree Standardization Task Force of the National Society of Genetic Counselors.1 (See also 5.8.3, Legal and Ethical Considerations, Protecting Research Participants’ and Patients’ Rights in Scientific Publication, Rights in Published Reports of Genetic Studies.)

A square represents a male individual; a circle, a female individual; and a diamond, an individual whose sex is unknown:

Shading indicates an affected individual. Partitions with different shading should be used for individuals with more than one condition. Define all shading in a legend or key.

Multiple individuals are indicated by a number inside the shape. For unknown number, a roman n is preferred to a question mark:

A slash mark indicates a deceased individual:

An individual in gestation is indicated with a capital P inside the shape:

The proband (“first affected family member coming to medical attention”1[p746]) is indicated by a capital P with arrow:

The consultand (person seeking medical attention) is indicated with an arrow:

Textual information appears below the individual symbol. Preferred order is age information, evaluation, and pedigree number:

An obligate carrier (ie, unaffected individual inferred by pedigree analysis to carry a trait) is indicated with a central dot:

A small triangle indicates an individual in a pregnancy not carried to term. Sex, if known, is indicated with text. Shading is used as described above for affected individuals. “ECT” indicates ectopic pregnancy. A slash indicates termination of pregnancy.

Stillborn individuals are represented by full-sized shapes with “SB” in the caption:

Partner relationships are indicated by a straight, horizontal line. It is preferred that the male partner be shown on the left.

Siblings should appear in order of birth (oldest to the left), connected by lines as follows:

Offspring are indicated by vertical lines; a shorter line indicates a pregnancy not carried to term:

An ended relationship is indicated by a double slash:

Consanguinity (“kinship because of common ancestry”2[p401]) is indicated by a double line:

Diagonal lines indicate twins. A horizontal bar specifies monozygotic; no horizontal bar, dizygotic; and a question mark, unknown:

No issue is indicated by perpendicular lines; infertility, by perpendicular lines with a double horizontal line.

Brackets indicate an adopted individual and dashed lines social parentage, eg, stepparent (example from Bennett et al1[p748]):

In pedigrees that show relationships defined by assisted reproductive technologies, D indicates donor (sperm or ovum) and S, surrogate carrier of the pregnancy.

Diagonal lines indicate other parental relationships:

Haplotypes may be indicated with shaded rectangles below the individual. Meaning should be clarified by means of a key.

A sample complete pedigree follows (Figure 6):

Figure 6. Pedigree showing 3 generations includes terminated relationship (double diagonal lines), condition common to father and 1 dizygotic twin son (half-shaded boxes), and haplotypes of mother and another son (rectangles with numbers). Roman numerals indicate generations.

References

1. Bennett RL, Steinhaus KA, Uhrich SB, et al. Recommendations for standardized human pedigree nomenclature. Am J Hum Genet. 1995;56(3):745-752. Also published in J Genet Counseling. 1995;4(4):267-279.Find This Resource

2. Stedman’s Medical Dictionary. 27th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2000.Find This Resource

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