Researchers are learning that nearly all conditions and diseases have a genetic component. Some disorders, such as sickle cell disease and cystic fibrosis, are caused by variants (also known as mutations) in single genes. The causes of many other disorders, however, are much more complex. Common health problems such as heart disease, type 2 diabetes, and obesity do not have a single genetic cause—they are influenced by multiple genes (polygenic) in combination with lifestyle and environmental factors, such as exercise, diet, or pollutant exposures. Conditions caused by many contributing factors are called complex or multifactorial disorders.
Although complex disorders often cluster in families, they do not have a clear-cut pattern of inheritance. It may be difficult to identify the role of genetics in these disorders, particularly because families often also share environments and may have similar lifestyles. This makes it difficult to determine a person’s risk of inheriting or passing on these disorders. Complex disorders are also difficult to study and treat because the specific factors that cause most of these disorders have not yet been identified. Researchers continue to look for major contributing genes for many common, complex disorders.
Topics in the Variants and Health chapter
- What is a gene variant and how do variants occur?
- How can gene variants affect health and development?
- Do all gene variants affect health and development?
- What kinds of gene variants are possible?
- Can a change in the number of genes affect health and development?
- Can changes in the number of chromosomes affect health and development?
- Can changes in the structure of chromosomes affect health and development?
- Can changes in noncoding DNA affect health and development?
- Can changes in mitochondrial DNA affect health and development?
- What are complex or multifactorial disorders?
- What does it mean to have a genetic predisposition to a disease?
- How are gene variants involved in evolution?
- What information can statistics provide about a genetic condition?
- How are genetic conditions and genes named?
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