Genetics questions

We had a couple of interesting genetics related questions from Tim that we decided it was worth making a full post about.

The first was "So genes do change to take account of environmental factors then where does that leave the inuit peoples who have low incidence of MS and a shortage of sunlight?"

The environment can influence the genome in at least three ways which differ in timescales:

Genes change over time (generations) as a result of natural selection (genetic variants that give us an advantage to live in certain conditions become more common over time). An elegant recent study comparing the genomes of 61 different populations across the world has shown how our genomes have adapted to the different climates over the world.

Within our own lifetime, the environment influences our epigenome (chemical changes to the DNA sequence). A recent notable example is how smoking influences DNA methylation (adding of methyl groups) of the F2RL3 gene.

We will spend more time talking about epigenetics in the near future.

More immediately (within minutes/hours), genes respond to the environment through gene-environment interactions. For example we have shown that circulating vitamin D controls the levels of genes involved in MS.

Inuit populations such as those in Canada live at high latitudes (and thus low sunlight exposure) but have a low rate of MS. In fact the only cases of MS identified in this group are from people who have a mixed race background (Caucasian and Inuit parents). This may argue that vitamin D may not be important for MS. However, Inuits have a very,very high frequency of a gene that is strongly protective for MS- this is the concept of a gene-environment interaction- you need the 'wrong' genes being exposed to the 'wrong' environment. Having just the genes or just low vitamin D is not enough- you need both.

If vitamin D is a factor the Swedish migrant study would have had different results, would it not?

No, again this is the same gene-environment concept as before. Iranians for example have a similar genetic background to Caucasians (they carry a high frequency of MS risk genes), but in Iran they are not as likely to be exposed to sunshine/vitamin D deficiency as they are in Sweden. In Sweden they have the wrong environment, which acts on their genes and increases their risk of MS.