multifaktorielles

Multifaktorielles (multifactorial) refers to traits or conditions influenced by many genetic factors in combination with environmental influences. Unlike traits caused by a single gene, multifactorial traits show continuous variation in the population and do not segregate in simple Mendelian patterns.

Genetic contribution arises from the combined, additive effects of numerous genes, often with small individual effects. Environmental factors such as nutrition, exposure to toxins, and lifestyle modify expression and liability. Many multifactorial conditions follow a liability-threshold model: individuals carry an underlying, normally distributed liability determined by genes and environment, and disease manifests only when liability exceeds a certain threshold. This model explains why relatives have higher risks without obeying simple Mendelian ratios.

Heritability estimates measure the proportion of variation due to genetic factors, but they depend on populations and environments. Family studies, twin studies, and, more recently, genome-wide association studies (GWAS) identify many contributing loci, each with small effect. Polygenic risk scores combine effects of multiple loci to estimate individual risk and can inform screening and prevention, though predictive power varies by population.

Examples include height, body mass index, skin color, and many common diseases such as type 2 diabetes, coronary artery disease, neural tube defects, and schizophrenia. These traits illustrate how genetics sets a background susceptibility that interacts with the environment to shape outcomes.

Clinical implications involve risk assessment and counseling, public health planning, and personalized medicine. Limitations include incomplete knowledge of gene–environment interactions and population differences.