A faulty gene means Gaby Koppel carries a high risk of female cancers. Taking no chances, she's had her breasts and ovaries removed – but how can she help her children with the choices they face?

Twenty-five years after my aunt died of cancer, I found myself sitting in a hospital consulting room facing a pair of young doctors. The two women exchanged nervous glances.

"We have your blood test results," said one, "and I'm afraid it's positive." Apparently, I'd inherited a faulty gene that put me at high risk of sharing my aunt's fate, and the medical advice was as clear as it was brutal: consider having your ovaries and breasts removed. Despite misgivings, I went ahead with the first operation, but before the surgeons could get to my breasts I found a lump. That quickly removed any residual doubts, but also raised a lot of questions about what I might have passed on to my own three children.

As I watch them grow up, I'm constantly aware that they may be forced to make difficult decisions at a much earlier age than I was. Hannah Fitzpatrick of Birmingham had a double mastectomy at 19, exactly the age my eldest is now. My daughter is in South America on a gap year, her Facebook photos show her trekking across moon-like landscapes, laughing with friends; there are art galleries, waterfalls and (much to our horror) skydiving. I'm appalled at the thought of having to bring her down to earth with such a horrible bump.

The embarrassing truth is that I've dodged every opportunity to discuss this with her before. When she was 12, I watched the expression on her face with a sense of rising panic as she thought it through. "Hang on then," she said, "that means I could..."

"Oh, you don't have to think about that until you are much older," I blurted. At the time, my husband and I were still reeling from the shock of dealing with my illness and the havoc it had wreaked in our young family. As the years rolled by, we remained reluctant to bring the subject up.

Children of carriers have a 50/50 chance that they will inherit the faulty gene. Jackie Harris of Breast Cancer Care says there's no "right" age to start talking to them about it. "But there is good evidence that children cope better when a family is willing to discuss what is happening. They respond to being given small amounts of information gradually, answering questions, and if you don't know the answer to something, be honest, say you will try and find out."

Of course, she's right. Maybe it isn't the best idea to do that on a wonky mobile signal across continents, but I'm determined to make up for past failings. Checking the time difference with Argentina, I call her number. No reply. I put down the phone and start tapping out an email.

The genes linked with breast and ovarian cancer, BRCA1 and BRCA2, are tumour suppressors; any one of hundreds of possible faults in them can multiply an individual's risk of cancer. They were first identified in 1994 and 1995, by which time one of my aunt's daughters had fallen ill, and we'd begun to wonder if that was mere coincidence. Of course I'd heard about successive generations of women succumbing to the same fate, but there was no consistent pattern in our family. When I became the sixth close relative to get ill, we worked out that the rogue gene had been passed on by our grandfathers and my father. Slipping silently through the male line, it created a blip in our family tree that camouflaged the poison seeping along its branches. We've now discovered that Ashkenazi Jewish families such as ours are at a much higher risk of carrying the faulty BRCA genes.

Despite my illness, I'm lucky that medical advances came in time to save me from worse (so far, touch wood). But I'm grateful for something else, too: that I didn't know any earlier. It wasn't until after having my son when I was 41 that I was forced to consider surgery that would terminate my ability to bear or feed children. I doubt I would have dared to leave it that long if I'd known the risk I was running.

Before the surgery, I was on an intensive screening programme designed to spot malignancy early. My children will benefit from newer scientific advances as well – when they are ready to have babies themselves, genetic testing could be used to select healthy embryos. That would ensure their children don't inherit, and the gene's pathway through our family will be stopped.

At bedtime I gently raise the subject with my younger daughter. "It's too early for me to really start panicking, but I do want to think about it," she says cautiously. But even at the age of 15, she hates the idea of screening embryos because it involves IVF and she wants to conceive naturally.

Jackie Harris says it's important to talk to my 12-year-old son about it, too, even though he may not be directly affected. "Make sure he's aware of the implications for any future children, but also so that he feels part of the family and feels respected and mature enough to be involved in all of this." Male carriers may also have an increased risk of some cancers.

It's important to speak to the whole family, including my husband. After all, he has been deeply affected by my cancer, too, and I realise I should have consulted him before broaching the subject with the children. But when it comes to testing, it's their decision and one they can take only when they are old enough, albeit with all the support we can offer. For young adults, testing positive can alter life plans by bringing on a real sense of urgency. It could catapult them into some extremely serious, grown-up decisions.

Harris says her concern is that expert counselling is needed as different issues arise through life, and there's a huge shortage round the country.

Annette Solomons agrees: "You need a psychologist to help you through this, because how else do you tell your children that they've got this potential death threat hanging over them?" Both her mother and grandmother died of ovarian cancer when they were 49, and Annette has survived breast cancer twice. "It's so much easier for the one in eight women who get normal breast cancers. They can put it behind them, but we have it hanging over us, generation after generation."

Annette says she spent hours in tears, agonising over how to tell her daughter. But Laura, then 14, worked out the truth after studying genetics in her science class. "She wanted to go straight to the hospital's counsellor. She's always been a very determined person." At 22, Laura tested positive, and she had a double mastectomy two years later. "My daughter is in a rush. She wants to have children one after another, then a hysterectomy. She wants rid of those bits that are life-threatening."

But how will my daughters react? The following day, the younger one calls from school, crying because she's left her art folder on the bus. "And Mum," she says, "I've been thinking about the cancer thing and it's really scary." My heart sinks. She's too young. Why didn't I keep my big mouth shut? Jackie Harris reassures me.

"You need to go back to her and say, 'Look at your relatives and see how well they are.' Because we are in an age where research is making huge strides forward and better treatments are available."

When my girl comes home from school I'm ready and waiting. But it turns out I've underestimated her. She's discovered that two of her friends have the same problem in their families, and talking to them seems to have made it easier to handle. In counselling speak, the situation has been "normalised" for her.

Late that night, an email pings into my inbox. It's from Bolivia, where the skydiver has just emerged from a 14-hour bus ride. Nervously, I open it, expecting recrimination. But instead it's extremely thoughtful. She insists that I did explain the problem when she was younger, though shielding her from the darkest details. "I think about it only very occasionally, but when I do I get a sinking feeling in my stomach like I've just found a time bomb strapped to my back. However, I feel in some ways safer than the Average Jo... at least I am aware that I am at risk, and can therefore take extra precautions.

"I don't think this gene changes my life plan at all. Why should it? I don't want to bow to a genetic defect that hasn't yet reared its ugly head. I am, though, approaching an age where I feel I deserve access to all the information you have available."

I breathe a sigh of relief. She's so much more level-headed than I could have hoped. It almost sounds as though she's pleased that I raised the subject. Harris isn't surprised: "Sharing and being open about the information helps them to make choices. Most genetic counsellors say that talking about it brings families closer."

A deadly inheritance: how to tell the children

* In families where there is an inherited risk of cancer, children cope better when the family is willing to discuss what is happening, according to Alison Metcalfe, professor of health care research at King's College, London.

* There is no "right" age to bring up the subject with your children, but try not to keep secrets, Professor Metcalfe advises.

* Talk to the whole family, not just those directly at risk.

* Each child's needs varies according to developmental stage. Gradually build children's knowledge – they may need to hear an explanation several times.

* Check their understanding, because children worry about upsetting their parents so may not ask all the questions they want to.

* Give the name (BRCA1/BRCA2 gene), as knowing it can help give children a sense of control.

* Reassure that carrying the gene is not the same as having cancer.

* Discuss any information children find on the internet or in newspapers.