Multifactorial inheritance means that many factors (multifactorial) are involved in causing a health problem. The factors are usually both genetic and environmental. A combination of genes from both parents plus unknown environmental factors make the trait or condition. Multifactorial traits do happen in families, because they are partly caused by genes and shared environmental factors. But they might now follow recognizable patterns. The chance of a multifactorial trait or condition happening to you depends on how closely the family member with the trait is related to you. For example, the risk is higher if your parent or sibling has the trait or disease than if your first cousin has the trait or disease. Family members have a certain portion of genes in common, depending on their relationship. For example:
Degrees of relationship
Percentage of genes in common
parents, children, siblings
aunts, uncles, nieces, nephews, grandparents
An example of a multifactorial trait is height. Some people may be very short or tall, often because of a change (mutation) in a single gene that has a major effect on height. But most of the time, a child's height is similar to, or somewhere between, the parents' height. Diseases such as diabetes, high blood pressure, or cancer are multifactorial. Some cancers cluster in families as the result of a combination of genetic and shared environmental factors (multifactorial influences). In such cases, the closer in relation a family member with cancer is to you—the more genes you share—the higher your chance to also develop cancer. In other words, it is more significant for your personal health if one of your parents or siblings gets cancer or another disease than if your second cousin gets the disease.