Does a Pedigree Chart Include Cousins?
Yes, pedigree charts can and do include cousins when they are relevant to the genetic assessment being performed. The standardized pedigree nomenclature explicitly addresses cousin relationships, particularly in the context of consanguinity and genetic risk assessment 1.
When Cousins Are Included
Cousins should be included in a pedigree when they affect the genetic assessment or when consanguineous relationships exist. The National Society of Genetic Counselors' standardized nomenclature specifically states that if the degree of relationship is not obvious from the pedigree structure, it should be explicitly stated (e.g., "third cousins") above the relationship line 1.
Key Principles for Including Extended Family
Multiple previous partners and extended family members do not need to be shown if they do not affect genetic assessment 1
The scope of the pedigree is determined by clinical relevance, not by arbitrary family boundaries 1
Consanguinity notation is specifically designed to capture cousin relationships, as these are critical for assessing autosomal recessive inheritance patterns 1
Practical Application
In clinical practice, cousins are commonly included when:
Evaluating consanguineous marriages (first cousins, second cousins, etc.), which significantly impacts genetic risk calculations 2
Assessing inheritance patterns where affected cousins help establish disease segregation in the family 3
Mapping complex traits where cousin relationships provide valuable linkage information 3
The pedigree structure naturally extends to include them when documenting multiple generations of a family 1
Important Caveat
The extent of cousin inclusion depends entirely on the clinical or research question being addressed. A focused pedigree for a specific genetic condition may only include first-degree and second-degree relatives, while a comprehensive genetic evaluation may extend to third cousins or beyond when relevant to the inheritance pattern being investigated 4.