Multifactorial inheritance, also called complex inheritance, can be attributed to a combination of genetic (ie single gene, multiple genes), environmental and lifestyle factors.
The number of necessary factors, and the impact those factors have on the presence or severity of a condition, will vary for different conditions and individuals.
Often, when there are multiple susceptibility genes involved, there is an additive effect on the outcome.
Early onset of conditions, such as cancer, cardiovascular disease or type 2 diabetes, may be indicative of multifactorial inheritance within a family.
This type of inheritance does not follow a characteristic pedigree pattern, but may look like autosomal dominant inheritance with incomplete penetrance.