Nature and nurture
Most conditions involve an interaction between genes and environment
Almost everything to do with health is affected by genes. Most often, the effect of an individual genetic variation is small and influenced by additional external factors: diet or exercise; exposure to a virus, bacterium or radiation; or a more general challenge, such as heat stress or exhaustion.
For example, people who develop the cancer mesothelioma have almost always been exposed to asbestos, the fibres of which lodge in the lungs. Some people who are exposed will be at a higher risk because of minor genetic differences. A 2013 study identified ten genetic variants that may contribute to a person’s risk, although they might not be the only ones.
Some genetic differences have mixed costs and benefits. There are a number of known mutations in the gene for the blood’s oxygen-carrying DNA haemoglobin. Carrying one altered copy of the gene can help to protect against infection by the parasite that causes malaria. However, carrying two altered copies (and hence no normal haemoglobin) can lead to diseases, including sickle-cell anaemia or thalassaemia.
Cancer cells have aberrant genomes, usually as a result of a series of genetic changes that happen as the disease develops. In the first step, normal cells may be exposed to chemicals that damage DNA or interfere with its repair. For more on the influence of genes and environment on disease, see Understanding the links.Lead image:
EM Unit, UCL Medical School, Royal Free Campus, Wellcome Images CC BY NC ND
- Genetic variants associated with increased risk of malignant pleural mesothelioma: a genome-wide association study (2013)
- WHO fact sheets: sickle-cell anaemia and thalassemia
- What causes cancer?
- Inside Cancer: a multimedia guide to cancer