Single nucleotide polymorphisms – a single change in the DNA code

Some diseases seem to run in families, suggesting that there might be a genetic link. Sometimes the DNA change only involves a single base. This is called a single nucleotide polymorphism (SNP).

Identifying SNPs, involves screening the DNA of thousands of different people, including those who have the disease and those who don't. Computers can then be used to check for particular DNA sequences that are found only in people who have the disease.

Currently there are about eight different SNPs known to increase the risk that a person will develop Crohn's disease.

Transcript

Dr Julian Heyes ()

The focus for our work is something called single nucleotide polymorphisms, SNPs [“snips”] for short — very, very minor genetic differences which don’t completely prevent a gene acting, or don’t produce an inactive protein, but which produce a protein perhaps which has a higher or lower affinity for its substrate. That means it doesn’t show up as an obvious single gene defect that someone has, and they will automatically get a disease, and we have to completely overcome their gene defect. It’s much more like a predisposition, or a risk factor. It seems as though are a number of SNPs which affect genes in your body, which predispose people to develop Crohn’s disease. There are perhaps 8 different ones at the moment. There are probably more, known to be associated with Crohn’s disease.

Dr Andrew Shelling ()

So what we do is we take our patients with Crohn’s disease, and controls that don’t have Crohns disease, sequence the genes that we are interested in, and look to see if there are any differences between the Crohn’s patients and the controls in the regions that we are really interested in.Once we find a difference we have some other more sophisticated methods to suddenly see if the patients all have a certain nucleotide change, or a change – a mutation – in their DNA, at a certain point. We can then very quickly set up a straightforward assay [chemical test] to look for that specific nucleotide change in all the patients and all the controls.