I've got my father's eyes, my mother's chin and an annoying kink in my hair that I recognise in a picture of my grandmother. But it's not just looks that get passed on: our susceptibility to disease is also inherited.
Largely ignored in this country, family health history is something of a national obsession in the US. Geneticists at Wisconsin University recently announced that they can create individualised genetic printouts that will be on sale for less than $100 within three years.
And for the last couple of years, the medical profession has stressed the importance of knowing your family history as "the cornerstone of efforts to prevent disease and save lives". In November 2004, the US Surgeon General, Dr Richard Carmona, urged his fellow Americans to use family reunions such as Thanksgiving dinners as an opportunity "to trace illnesses suffered by parents and other blood relatives".
The more information each person is able to collect, the more useful it will be, he explained. Already, nearly a million people have complied, entering the information they gather into an interactive website (www.hhs.gov/familyhistory), to draw up a "health graph" that they can show to their doctor.
Now that I am becoming a grandmother for the first time, perhaps I should see it as my duty to gather as much data as possible about the state of the ancestral arteries and overall susceptibility to disease - rather than just knitting the odd shawl.
On the face of it, this American desire to get the genes out in the open seems sensible. A study has shown, for instance, that one in eight American families accounts for half the number of heart attacks. Whether such families inherit a tendency to high blood pressure or a preference for junk food is beside the point: knowing you belong to such a family is the start of making the right changes. "Getting advice from your doctor on preventing premature death from heart disease has more of an impact when you can see your risk of developing the disease in a graph in front of you," says Dr Mike Murray, clinical chief of medical genetics at Boston's Brigham and Women's Hospital.
British doctors are more sceptical of the benefits of making us overly conscious of our susceptibility to disease. A recent British Medical Journal cartoon showed a picture of two ageing ladies smoking and boozing. One says: "Cancer? Frankly darling, I just don't have the gene for it" - to which the other replies: "Well actually, darling, I do, but I simply don't care."
Health psychologists say that there is not enough evidence yet to know how people will react to more knowledge about their genes. "Learning more about your genetic risk, whether it's through a DNA test or getting to know more about your family history, could be motivating, or it may make you fatalistic," says Professor Theresa Marteau, director of the Psychology and Genetics Research Group at King's College, London.
She is currently investigating the impact of genetic information on behaviour in two large trials, and until they are completed, she says, there is not enough evidence to suggest which people will benefit from getting different kinds of information and advice. What's more, even the Wisconsin geneticists acknowledge that a full knowledge of one's own genome will not bring cures or effective prevention of these distant threats, but merely "allow doctors to give personalised advice on their diets, lifestyles and medical check-ups".
The concern in the UK is that this development will lead to an increase in the growing number of worried well, for whom little of value can be done.
Take my own family. With an Ashkenazy Jewish grandmother who died in her thirties of breast cancer, and an aunt, her daughter, who developed (and survived) it in her late forties, there's a one in two chance that I have inherited a breast cancer gene mutation (BRCA1 or BRCA2) that is common in this racial group - thus pushing up my lifetime risk of developing breast cancer from about one in 12 (the average lifetime risk for a woman in the West) to four in five.
In theory, such information should be useful. Earlier this month, the Human Fertilisation and Embryology Authority gave the go-ahead for couples with this genetic risk to be allowed IVF and embryo selection to prevent the gene being passed on. What's more, there is a prophylactic therapy available for women who are already living with the gene: double mastectomy, preferably with ovaries removed as well - though there's no guarantee that it will work.
It seems extraordinary to me, however, that anyone would contemplate such extreme "therapies" - not least because neither guarantees good health nor even the avoidance of breast cancer. If I haven't inherited one of the BRCA genes (as seems increasingly likely) then I still face a slightly increased risk of developing cancer. Having one close relative develop cancer at any age increases an individual's risk of developing cancer by around 14 per cent, in someone with two close relatives with cancer, the extra risk is just over 20 per cent.
At the other extreme, there's also heart disease in the family, another area where scientists are "close" to a breakthrough in identifying the range of DNA involved. One major ongoing study is trying to identify the genes that make people susceptible to smoking-related diseases. Another has reported on the half a dozen "culprit genes" that increase the risk of a heart attack in middle age.
Yet there are simpler ways for an individual to check their risk of heart disease. The current older generation of my own family doesn't need to worry too much about our family history. Blood pressure and cholesterol checks are the best way to identify a potential risk of having a heart attack - and those of us that need to are already taking statins.
It should come as no surprise that behind this push to make people more aware of inherited disease is a developing industry with a vested interest in a gene-conscious population. On the one hand, genetically tailored smoking-cessation and weight-loss products are already in the pipeline. And the new science of "nutrigenomics", with its range of food products tailored to people's genetic profile, is already causing waves of excitement at scientific conferences around the world.
Alongside the buzz, however, is concern about how expensive such products are compared to more mundane but potentially more effective strategies. "The idea of investing public funding in individualised nutritional products that tweak beneficial or undesirable aspects of our genetic predisposition is absurd in a country with a high incidence of saturated fat-related disease - especially in a country that is failing to take action to reduce the production of fatty foods," says Tim Lang, professor of food policy at City University.
All of which is not to say that genetic medicine has nothing to offer. There are no doubt major breakthroughs in the pipeline that may provide acceptable treatments for inherited cancers and other diseases. An awareness of family health history may also prove a useful tool in health promotion, once the research to back it up has been carried out.
Meanwhile, a cautious approach to the benefits of genetic testing seems sensible - particularly when it comes to priorities for funding. Take the well-equipped local authority gym that recently opened down the road from me, which is much cheaper to use than a private health club. Such a facility should do more to cut the risk of heart disease and cancer for local grandmas and grandchildren alike than any amount of spending on nutrigenomics or genetic testing.
Five ways to screen your genes
Embryo testing (pre-implantation genetic diagnosis or PIGD)
For couples at high risk of passing on a serious genetic disease such as cystic fibrosis or haemophilia who are prepared to undertake embryo screening as part of an IVF cycle. It's not available on the NHS and each procedure requires individual approval by the Human Fertilisation and Embryo Authority. There have been less than 100 births using PIGD so far in UK.
Blood test in adults
For close relatives of people diagnosed with an inherited disorder where a single gene has been identified. These include:
* Huntington's disease: a genetic blood test for this progressive disease, which affects people from their thirties onwards, passed on via a single gene from one parent, has been available for more than a decade. With no treatment available, only around 18 per cent of children of diagnosed sufferers opt to have the test.
* Familial adenomatous polyposis coli (FAP): a blood test can pick up about 85 per cent of people at risk of this rare and severe form of bowel cancer - but it is normally used in families of people diagnosed with the disease.
* Five per cent of cases of breast cancer are caused by a mutation of the BRCA1 or 2 gene, increasing the 12 per cent lifetime risk facing Western women to around 80 per cent. With at least 100 different mutations of this gene, it is difficult to test for without a blood sample from a close relative.
For close relatives of people diagnosed with a treatable inherited disorder where there is no genetic test as such. The test covers disorders including:
* Familial hypercholesterolaemia (inherited high cholesterol)
* Sudden cardiac death
* Fragile X syndrome (inherited mental impairment)
More frequent conventional screening for anyone whose family history suggests they have a high risk of developing diseases including:
Bowel, breast and ovarian cancer for people who have more than one relative who was diagnosed with the disease under the age of 50.
Heart disease in people who have one or more relative who was diagnosed in men under the age of 40 and women under 50.
Commercial genetic testing
Widely available in the US and on the internet, attempts to sell unregulated and unproven genetic tests linked with dietary advice, either on the high street or through alternative practitioners and GPs, have been banned in the UK.Reuse content