The identification of genetic variants predisposing to complex diseases and phenotypes represent a challenge for geneticists in the early part of the 21st century. These are not simple Mendelian disorders caused by single mutations, such as cystic fibrosis or Huntington's disease, but common diseases that are usually polygenic in origin. The predisposing genes can be susceptibility factors or protective factors. One example of such a complex disease is the inflammatory skin disease psoriasis. However, another example could be protection from an infectious disease. Both of these phenotypes are due in part to the presence of low-risk variants in the host. Moreover, all of these complex phenotypes require environmental triggers as well and, in the case of infectious diseases, these are pathogens. In the case of other common diseases such as cardiovascular disease the triggers are often lifestyle-related issues such as diet or exercise. Genome-wide association studies are now identifying some of these genetic susceptibility factors.
- Risk factors