Penetrance

In genetics is understood penetrance the percentage probability that a particular genotype leading to the formation of the corresponding phenotype.

Complete and incomplete penetrance

A distinction is made between complete penetrance, in which it always comes to the expression or manifestation of the feature, and incomplete penetrance, in which not manifest despite the presence of genotype characteristics of the associated phenotype in each case. Background of incomplete penetrance ( <100%) may be modifying genes, environmental factors, or even the chance.

Concordance and discordance

Incomplete penetrance can be the manifestation of a characteristic probability calculated. An auxiliary variable is the number of concordance in monozygotic twins (DC). Concordance means that the same features occur in phenotypically EZ, unconformity, if this is not the case, see also → twin research.

Penetrance and expressivity

The penetrance is a categorical feature, thus refers only to the question whether a genotype associated phenotype is present or absent. The degree to which an obtrusive allele expresses a characteristic in the phenotype is referred to as genetic expression.

Practical significance

The penetrance of an allele influences the disease risk for children of carriers of a hereditary disease.

Assessment

The description of a mode of inheritance with incomplete penetrance is not an indicator as to which mechanisms are responsible for the expression or non- expression of the characteristic. The assumption of simple Mendelian inheritance is particularly useful in cases where the penetrance is less than 50 percent, often not justified. In such cases, the alternative hypothesis of a multifactorial inheritance in must be considered. For this purpose, the inheritance is by means of the heritability often precisely describable.

Examples

• Neurofibromatosis, virtually 100 % penetrance
• BRCA1 gene -dependent breast cancer ( in women), clinically about 8.5 % penetrance.