Genetics of complex disease

To find true genetic associations in complex diseases, such as allergic rhinitis and chronic rhinosinusitis, is a difficult task. Both are polygenetic diseases where it is believed that genetic variation in several genes make up their phenotypes. In addition, the environment of the affected individuals also play an important role, further obscuring eventual associations. Today most genetic association studies of polygenetic disease perform tests on the whole-genome level, but this has not always been the case. By 2012 a total of 56 genetic association studies had been published in allergic rhinitis and by 2013 a total of 27 studies in chronic rhinosinusitis. In but a few exceptions, all studies of the two diseases targeted candidate genes in small case and control groups. Replication attempts of significant associations from previous studies has shown some promise by pointing out more likely candidates. However, these associations do not explain the heritability of the studied diseases to any great extent. To find this missing heritability researchers have to look beyond common variants and instead focus on other potential targets. Re-sequencing studies of candidate genes could find rare variants with much higher effects sizes and studies of RNA and proteins should also prove to be helpful. New technologies and advances in molecular biology are looking promising but it is still hard to interpret all the new data. Polygenetic disorders are hard to study, low effect sizes makes novel candidate genes hard to discover. However, it is a numbers game, as more and more studies are made, more information will be available and eventually the genetic component, however big or small it is, of complex diseases will be solved.