Genetics Overview

How do genes cause or contribute to disease?

There are many ways genetic differences can affect the way the body functions. The genetic difference may cause the body to make something incorrectly, make too much of something, or make something when it is not needed. Or, maybe the difference is so severe that it prevents the body from making something it needs. When and how the genes are used can also be impacted by the environment. For example, lactase is a digestive enzyme that digests the sugar in milk (lactose). Thus, lactase digests (breaks down) lactose. The amount of lactase that is made depends on how much milk a person drinks. The environment (aka the milk that comes in) impacts the activity of the gene that makes lactase. Those who drink a lot of cow’s milk make a lot of lactase. On another note, some people have differences in their genetic code that affect their ability to make lactase. These people have difficulty digesting milk because of it. This is known as lactose intolerance.

How genes impact disease can be organized into three categories: single gene disorders, complex disorders, and environmental disorders.