Just over a year ago, Iceland’s deCODE Genetics kicked off a new era in personalised genetics with the launch of a direct-to-consumer service dubbed deCODEme.

A few days later, California’s 23andMe launched its own service with the slogan: “Genetics just got personal. Don’t worry. We’re here to help.” In November 2008, that company’s service was named Time magazine’s invention of the year.

For less than $1000, deCODE and 23andMe offered customers the opportunity to take a gander at their unique genetic quirks and glitches, as revealed by the identities of more than 500,000 single nucleotide polymorphisms (SNPs).

Such services would have been unthinkable just two years ago, before the explosion of genome-wide association studies (GWAS) began pinpointing susceptibility genes for common, complex diseases such as cancer, heart disease, diabetes, and mental illness.

Some of the attraction of these web-based services is undoubtedly recreational – what’s my haplogroup? Do I have fast-twitch muscles? Am I a fast or slow caffeine metaboliser?

Some people may be curious about tracing their family’s roots or comparing genomes to friends and family members. Adoptees may be interested in gleaning something of their biological background.

But these services, which now include offerings by Navigenics and SeqWright, translate the latest peer-reviewed genomic research into estimates of individualised disease risk, potentially allowing consumers the opportunity to confirm indications from their family history or revealing wholly unsuspected predispositions to a given disorder.

The proselytisers of personal genomics acknowledge that these services are works in progress, but some anecdotal results have been remarkable.

Last year, deCODE Genetics co-founder Jeffrey Gulcher, 48, reviewed his deCODEme data, which indicated he had a doubled lifetime risk for prostate cancer. Even though his PSA levels were fairly normal, Gulcher ended up getting a biopsy that revealed a grade 6 (Gleason scale) prostate carcinoma, which was successfully resected.

“This test may have saved his life,” deCODE CEO Kari Stefansson said.

The co-founder of Navigenics, Los Angeles physician David Agus, received similarly alarming results when he took his firm’s Health Compass analysis – an 80 per cent risk of a heart attack. He told guests at the Navigenics launch party that he began taking appropriate lifestyle, dietary and medical action.

Sergey Brin, the co-founder of Google and husband of 23andMe co-founder Anne Wojcicki, recently disclosed that he carries a mutation in a Parkinson’s disease susceptibility gene called LRRK2. By searching all of his genotyped LRRK2 SNPs through his 23andMe account, Brin learned that he carried the same point G2019S mutation as his mother, who has Parkinson’s.

A handful of anecdotal stories is no substitute for hard data of course, and the consumer genomics industry has sparked deep concern among the medical establishment and certain regulatory agencies about the wisdom, validity, and legality of delivering medical information to consumers, and the public’s limited ability to interpret their odds ratios and relative risks without expert assistance.

Rather than fork out $1000 for a genome scan, the New England Journal of Medicine argued in 2008 that it made more sense to buy “a gym membership or a personal trainer” and implement dietary changes to reduce the risk of heart disease and diabetes.

In 2007, the state of California issued “cease and desist” letters to 13 consumer genomics providers, but while some firms retreated, the major providers satisfied the state that their tests were performed in CLIA-certified labs with appropriate physician oversight.

Regulatory rumblings notwithstanding, it is easy to overlook just what has been achieved in the past 12 months thanks to the collective efforts of what US bioinformatics company BioTeam’s Michael Cariaso dubs “23 et al”.

These genome scans are not, the providers stress, diagnostic tests, but a means of providing information that mirrors the stunning progress researchers are making in dissecting the genes underlying complex traits. Indeed for most genes, the individual effect on a person’s relative disease risk is minor.

One exception is Apolipoprotein E (ApoE), which was strongly associated with late-onset Alzheimer’s disease by Duke University’s Professor Allen Roses and colleagues. This is the gene that James Watson had redacted from his genome sequence last year rather than learn his potential risk.

“The odds ratio of ApoE4 is 3.0, which is pretty substantive,” Boston University’s Robert Green, who is conducting a trial to study reactions to Alzheimer’s genetic testing, said. By contrast, most gene associations in complex diseases produce odds ratios of 1.1 or 1.2 and thus have limited significance by themselves. “But people who are not statistically sophisticated will not necessarily understand that," Gren said. "All they’ll see is that the risk is higher or lower.”

In 2008, I signed up for personal genomics services from the four main providers: deCODE, Navigenics, 23andMe and SeqWright. The firms’ philosophies may vary but the procedures are similar. The consumer’s DNA is surveyed on a commercial or customised Affymetrix or Illumina DNA chip for 500,000 to one million SNPs.

The results are delivered via the web and (with one exception) regularly updated as new findings are published. These services are now as cheap as US$399, thanks to 23andMe’s recent price cut.