What is a complex disease?

Many common diseases are influenced by a combination of multiple genes and environmental factors. These diseases are referred to as complex diseases.

  • Many of the most common diseases run in families and are caused by a combination of genetic, environmental and lifestyle factors.
  • These diseases are called complex diseases.
  • Although complex diseases tend to run in families, unlike single gene disorders, they do not have clear-cut patterns of inheritance so it is difficult to predict a person’s risk of inheriting or passing on these diseases.
  • Because they can be caused by both genetic and environmental factors, complex diseases can be difficult to treat.
  • Complex diseases include asthma, diabetes, epilepsy, hypertension, manic depression and schizophrenia.
  • Some developmental abnormalities are also included, such as cleft lip and congenital heart defects.
  • It is thought that the incidence of any complex disease is dependent on a balance of risks, too many negative genetic and environmental factors and the balance can be tipped towards disease.

Single nucleotide polymorphisms

  • Single nucleotide polymorphisms, or SNPs, are single letter changes in the DNA code.
  • SNPs are the most common type of genetic variation.
  • SNPs occur throughout the genome, on average there is an SNP every 300 bases.
  • Many genetic changes associated with complex diseases have been identified by looking to see if there are SNPs that occur more or less commonly in people with a disease, than people without the disease. This type of study is called a genome-wide association study or GWAS.
  • Identifying SNPs associated with particular diseases will enable scientists to predict an individual’s likelihood of developing a disease and how the disease runs in families.
  • These ‘risk SNPs’ can also help scientists to identify biological pathways underlying these diseases which can help with the development of treatments.

This page was last updated on 2021-07-21