proband

Proband is a term used in genetics and medical research to designate the person in a family who first brings a hereditary condition to the attention of investigators. The proband, also called the index case, serves as the starting point for a genetic study and for constructing the family pedigree to analyze inheritance patterns. In many cases the proband is a patient with the disease, but the designation can apply to an individual who prompts a family study, including asymptomatic carriers.

Etymology and naming: The word comes from Latin probandus, meaning “that which must be tested” or “that which should be proved,” derived from probare, “to test.” In pedigrees, the proband is often labeled propositus if male or proposita if female; the term proband itself is widely used as a gender-neutral designation.

Usage in research: The proband’s phenotype guides the investigation of how a trait is inherited within the family, helping to determine whether a trait follows, for example, autosomal dominant, autosomal recessive, or X-linked patterns. Studying relatives after identifying the proband can reveal penetrance, expressivity, and carrier status, informing risk assessment for other family members.

Other contexts: Outside genetics, proband may occasionally be used to refer to the subject of a study, but this usage is less common in modern psychology and social science, where terms such as participant or subject are preferred. The term is most closely associated with medical genetics and familial studies.