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Genetic disorders may also be complex, multifactorial, or polygenic, meaning that they are likely associated with the effects of multiple genes in combination with lifestyle 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.

On a pedigree, polygenic diseases do tend to “run in families”, but the inheritance does not fit simple patterns as with Mendelian diseases. But 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).

* asthma

* autoimmune diseases such as multiple sclerosis

* cancers

* ciliopathies

* cleft palate

* diabetes

* heart disease

* hypertension

* inflammatory bowel disease

* mental retardation

* mood disorder

* obesity

* refractive error


Adapted from the Wikipedia article Genetic disorder, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki