A number of companies now offer to conduct scans of a person's DNA over the internet searching for the genes associated to diseases such as Alzheimer's or breast cancer.

The scans search for up to 500,000 genetic "markers" that can indicate anything from the risk of heart disease to ethnic origins.

But medical specialists are warning there is a risk of people being misled about the results of such scans.

The specialists say the genome-wide scans on offer will provide little meaningful information because the science is still too preliminary.

They also believe the scans can mislead people into becoming either over-anxious about being labelled "high risk", or over-confident that they are at low risk of a particular disease.

Dr. Christine Patch, a consultant genetics counsellor at Guy's Hospital in London and a member of the Human Genetics Commission says the scans are a waste of money and people taking the tests believe that the information they are getting are a genetic prediction.

Companies such as DecodeMe, based in Iceland, offer a screening service typically costing hundreds of dollars, to calculate genetic risks for common conditions like cancer, diabetes and heart disease that involve multiple genes.

Customers send cheek swabs through the post and have access to the information via a password-controlled website run by DecodeMe.

Navigenics, based in Silicon Valley, California, and 23andMe, plan to offer a similar service.

A report by the Human Genetics Commission is calling on the government to ensure the tests used by these companies go through a more rigorous assessment process.

Scientists have already linked a number of genes to common diseases but these interact in a complex manner and their ultimate effect is influenced by environmental factors in ways that are as yet not clearly understood.

According to Stuart Hogarth of the Institute for Science and Society at University of Nottingham these new companies have substantial financial backing, and it highlights the growing commercialisation of the gene testing industry.

Hogarth says there is no regulatory framework that can control the burgeoning field, and there is a severe danger of losing public confidence in what is a very promising and very exciting field of science.