Editing Genetic disorder (section)

== Multifactorial disorder ==
{{main|Multifactorial disease}}
Genetic disorders may also be complex, multifactorial, or polygenic, meaning they are likely associated with the effects of multiple genes in combination with lifestyles and environmental factors. Multifactorial disorders include [[heart disease]] and [[diabetes]]. Although complex disorders often cluster in families, they do not have a clear-cut pattern of inheritance. 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. Studies that aim to identify the cause of complex disorders can use several methodological approaches to determine [[genotype]]–[[phenotype]] associations. One method, the [[genotype-first approach]], starts by identifying genetic variants within patients and then determining the associated clinical manifestations. This is opposed to the more traditional phenotype-first approach, and may identify causal factors that have previously been obscured by clinical [[heterogeneity]], [[penetrance]], and expressivity.{{cn|date=March 2023}}

On a pedigree, polygenic diseases do tend to "run in families", but the inheritance does not fit simple patterns as with [[Mendelian]] diseases. This does not mean that the genes cannot eventually be located and studied. There is also a strong environmental component to many of them (e.g., [[blood pressure]]).

Other such cases include:
* [[asthma]]
* [[autoimmune diseases]] such as [[multiple sclerosis]]
* [[cancers]]
* [[ciliopathies]]
* [[cleft palate]]
* [[diabetes]]
* [[heart disease]]
* [[hypertension]]
* [[inflammatory bowel disease]]
* [[intellectual disability]]
* [[mood disorder]]
* [[obesity]]
* [[refractive error]]
* [[infertility]]