Penetranssi

Penetranssi is a genetic term used in medical genetics to describe the probability that a given pathogenic variant will be phenotypically expressed in an individual who carries it. In other words, it is the proportion of mutation carriers who show the associated trait or disease. Penetranssi is distinct from expressivity, which refers to the spectrum and severity of symptoms among affected individuals. Penetranssi can be complete, approaching 100%, or incomplete, where only a subset of carriers develop the phenotype. Some conditions show age-related penetrance, meaning the likelihood of manifestation increases with age.

Estimating penetranssi relies on family studies, patient registries, and population data, and it can vary by population, sex, environmental factors, and genetic modifiers. High-penetrance variants make disease more predictable in carriers, whereas variants with reduced or variable penetrance complicate risk assessment. In clinical practice, penetranssi informs genetic counseling, screening strategies, and decisions about preventive interventions. A variant's penetrance can be uncertain, especially for newly discovered or poorly characterized mutations, and such variants are reported with lower confidence until more data accumulate.

Etymology: the term penetranssi derives from Latin penetrans, 'penetrating', and is used in Finnish-language genetics literature to describe phenotype expression among carriers. See also penetrance, expressivity, variable expressivity, and genetic modifiers.