They are caused due to effects of more than one gene in combination with environmental factors and lifestyle such as exercise, diet, or pollutant exposures and none of the genes involved is dominant or recessive.
These disorders are not confined to single gene inheritance but are dependent on a number of genes at different loci and are rarely treatable.
Common examples are diabetes, asthma, Alzheimer's disease, etc.
These disorders don't have a clear-cut pattern of inheritance and often cluster in families.
It is difficult to determine a person's risk of inheriting or passing such disorders.