Genetics Overview

Genes and Complex Disorders

Most disorders are categorized as complex. These disorders do not follow the same predicted pattern of inheritance seen in single gene disorders. Instead, they result from a complex interplay of genes and environment. If you’ve ever heard someone say that a disorder “runs” in their family, they are referring to a complex disorder. Examples of complex disorders include heart disease, diabetes, Alzheimer disease, autism, Parkinson disease, asthma, and spina bifida.

This type of inheritance is also referred to as multifactorial because many different factors, genetic and/or environmental, are involved. A person will have a complex disorder if he or she has the right combination of genetic differences and environmental exposures. Sometimes these disorders are caused by differences in more than one gene in combination with or without environmental factors. Examples of environmental factors include exposure to certain chemicals, medications, smoking, alcohol, stress, or diet. Close relatives of someone with a complex disorder have a higher chance of developing the disorder than the close relatives of someone who does not have the disorder.