We all carry hundreds of genetic mutations in our DNA

An average person carries roughly 400 potentially damaging mutations in their DNA, say geneticists. The findings from the 1000 Genome Project suggest approximately two of these mutations can be directly linked to the development of a disease.

'For over half a century, medical geneticists have wanted to establish the magnitude of the damage caused by harmful variants in our genomes. Our study finally brings us closer to understanding the extent of these damaging mutations', says lead author Dr Yali Xue from the Wellcome Trust Sanger Institute.

Scientists compared the sequenced genomes of 179 people to data held in the Human Gene Mutation Database (HGMD) on genetic mutations known to cause disease. The genomes analysed remained anonymous, so none of the specific findings were reported back to the participants.

Most of the disease-causing mutations identified were found to be 'silent', as the majority of participants carried only one copy of the mutation, where two copies would be needed to cause disease. However, researchers did show that in one in ten people the mutations present were enough to cause disease, though the effects were determined to be relatively small.

'In the majority of people we found to have a potential disease-causing mutation, the genetic condition is actually quite mild, or would only become apparent in the later decades of life', explained Professor David Cooper who led the study at Cardiff University. 'We now know that normal, healthy people can possess many damaged or even completely inactivated proteins without any noticeable impact on their health'.

Professor James Evans from the University of North Carolina, USA, who was not involved in the study, similarly remarked to NPR health blog: 'We're all mutants. The good news is that most of those mutations do not overtly cause disease, and we appear to have all kinds of redundancy and backup mechanisms to take care of that'.

The HGMD is not a complete collection of all disease-causing mutations. It is therefore likely that the current estimate for the number of potentially damaging genetic variations a person carries will increase as improved technology reveals previously unknown mutations.

Professor Cooper concludes: 'It is extremely difficult to predict the clinical consequences of a given genetic variant, but databases such as HGMD promise to come into their own as we enter the new era of personalised medicine'.

The study was published in the American Journal of Human Genetics.