DNA data for the price of a dinner

The two women are among 180,000 people who have paid to have their DNA analysed by 23andMe, the world's biggest private genomics company, to assess more than 200 genetic traits and health risks.

That number of customers is expected to soar this year after the California-based company, which takes its name from the 23 pairs of chromosomes in a normal human cell, reduced the cost of a testing kit to $99 last month.

The company, co-founded by Anne Wojcicki, the wife of the Google entrepreneur Sergey Brin, is planning to reach a million clients by the end of this year, including in Britain.

Kits similar to 23andMe are available in Australia online, through several companies, starting at about $300. The boom in business and interest in genomes and genetics has led to controversy about the commercial use of one of the most crucial medical breakthroughs of recent years.

For proponents, such as Ms Wojcicki, whose husband has a genetic mutation that significantly increases the risk of Parkinson's disease, this is the dawn of a new era.

For the price of a night out, individuals can learn key elements of their genetic composition and take treatment, or protect their children from hereditary health risks.

Critics, including doctors, bioethicists and geneticists, are concerned that people will be overloaded with information that is difficult for them to interpret.

''There are major concerns about the private genetic testing market,'' Helen Wallace, of GeneWatch UK, a genetic watchdog group, said.

''It is unregulated; much of the information people get is misleading or unreliable and genetic tests are a poor predictor of the big killer diseases. And there is also the danger of people receiving scary surprises - without the presence of a doctor …''

Mrs Kushnir, 69, who owns a chain of hair salons with her husband in Silicon Valley, said it was ''patronising in the extreme'' to say only experts could handle this sort of information.

The American Academy of Pediatrics expressed reservations about using the tests on children, except in limited circumstances. The American College of Obstetricians and Gynecologists has concluded that personalised genetic profiling is ''not ready for prime time''. But as the medical community tries to apply some rules, others are forging ahead.

Mrs Durrett, 53, from Roswell in Georgia, took the DNA test to try to determine the cause of some minor health problems. She discovered not only that she had breast cancer, but also that the man she had called ''Dad'' for 50 years was not her father.

Mrs Durrett tracked down her biological father and a half-sister, who had breast cancer. When an update from 23andMe revealed that she had an elevated risk of the same disease, Mrs Durrett went to her doctor. A subsequent biopsy found that she had cancer. ''If I'd waited, it would have gone into the tissue,'' she said.

Tests for various genetic predispositions in Australian public hospitals range from $30 up to about $1500 (for the price of a breast cancer test).

The chairman of Australia's Human Genetics Advisory Committee, molecular geneticist Ron Trent, said such products were wrongly presented as a preventive health measure but could cause unnecessary worry to families.

The companies' own websites include disclaimers that they are just an information source and not designed to diagnose, treat or prevent a disease or medical condition, or give medical advice.

''These tests are not black and white in trying to interpret them and that is why we have health professionals,'' Professor Trent said. ''The interpretation of these tests is really quite difficult and sometimes I'm struggling to know what it means and I do it for a full-time job.

''If you send your DNA overseas to a company, you've lost control of it in terms of privacy and what it could be used for,'' he said.

TELEGRAPH, with MARIKA DOBBIN