A surge in genetic testing here has people and authorities worried. The testing regime starts at birth, with a battery of mandatory tests that screen newborn babies for up to 44 congenital disorders, depending on the state in which they are born.

Some doctors fear that rolling out new tests for conditions that cannot be cured, or possibly even treated, risks scaring parents and stigmatising children. Despite this, Americans seem keen to unravel the genetic codes of themselves and their offspring, to the extent that here on the west coast there is now a flourishing genetics industry. At the last count there were more than 30 companies offering tests claiming to forecast future medical conditions or reveal ancestry.

The website www.23andme.com , for instance, analyses half a million DNA “locations” taken from a simple swab of saliva for $1,000 (£514). It predicts the likelihood of developing over 80 diseases and traits, ranging from diabetes and cancer to eye colour and even which foods you might prefer. The company also offers information about ethnic origins.

While the federal government has yet to regulate direct-access genetic tests, many states are worried about people making major lifestyle changes based on diagnoses that could be misleading or misunderstood. Does being told you are at low risk of a heart attack encourage you to guzzle hot dogs? And how are you meant to take a finding that you are susceptible to developing schizophrenia, especially when the analysis is based on a single medical study? Could it become a self-fulfilling prophecy? Residents of 11 states, including New York and California, are now forbidden to use online genetic test services without the permission of their doctors, although enforcing such bans is proving almost impossible. Genetic analysis has yet to become popular in the UK, but as home testing becomes ever easier and cheaper, its arrival in Britain seems inevitable. After all, for just $60 (£31), Americans can now even test their pets’ DNA to check whether their designer labradoodle is a pedigree pooch or mutant mutt. Crick and Watson would be proud.

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