Multifactorial inheritance is when more than one factor causes a trait or health problem, such as a birth defect or chronic illness. The main factor is genes. But the cause includes other factors that aren’t genes, such as:  

• Nutrition

• Lifestyle

• Alcohol and tobacco

• Some medicines

• An illness

• Pollution

Often one sex—males or females—is affected more often than the other for certain traits or disorders.

Multifactorial conditions tend to run in families. This is because they are partly caused by genes. Your risk for a multifactorial trait or condition depends on how close you are to a family member with the trait or condition.

For example, you’re at higher risk for a trait or disorder if your brother or sister has it. You’re at lower risk if a cousin has it. Family members share a portion of genes in common, depending upon their place in the family tree. Your parents, siblings, and children share about half of your genes. But because multifactorial disorders are caused by more than one factor, it’s hard to pin down a person’s real risk of having it or passing it on.

Health problems that are caused by both genes and other factors include:

• Birth defects such as neural tube defects and cleft palate

• Cancers of the breast, ovaries, bowel, prostate, and skin

• High blood pressure and high cholesterol

• Diabetes

• Alzheimer disease

• Schizophrenia

• Bipolar disorder

• Arthritis

• Osteoporosis

• Skin conditions such as psoriasis, moles, and eczema

• Asthma and allergies

• Multiple sclerosis and other autoimmune disorders

If you have family members with any of the above health conditions, talk with your healthcare provider about your risks. He or she can give you information about how to lower your risk for certain conditions, or how to manage a condition.