I can't remember a time when bipolar disorder didn't cause our family pain. Just after my parents divorced when I was six, my dad Jim was diagnosed with manic depression as it was then called. He spent the rest of his life (until he was killed in a car accident in 1987) in and out of psychiatric hospitals chain-smoking in his pyjamas.

Bipolar knocked on our family's door again in 1993 when my Aunt Irene, my dad's sister, was diagnosed. My cousin, her daughter Amanda, describes her usually gentle mother's first manic episode: 'She flung her clothes, photos and jewellery out of the bedroom window, then hurled herself against the living room walls, shouting that the IRA were coming to kill us.' Since then, Irene has been sectioned 14 times.

Twelve years ago, my sister Rebecca was also diagnosed with bipolar disorder. She has been sectioned several times — it usually happens after an overdose suicide attempt. Once she escaped from hospital and threw herself in front of a car. In 2003, she had such a severe breakdown she spent almost a year in a secure unit.

These low points of the illness — the breakdowns, suicide attempts, sections, hospital stays — are indelibly etched into our family's memory. Yet it's not just the crises that affect us.

Mental illness can have an insidious impact on family life every day, even during the 'good times'. Loved ones sometimes feel fearful, guilty and lonely. Amanda and I certainly do. Regardless of how well Rebecca or Irene are doing, it's hard to let go of the fear that trouble's brewing. If Rebecca's holding her glass out for more wine, we wonder if she's approaching a high. If Irene is slightly withdrawn, we get ready to call her psychiatric support team.

There's the guilt — the catalyst for Rebecca's first breakdown was my wedding. I returned from honeymoon in Jamaica to find my pale, trembling sister sectioned in a psychiatric unit. How guilty I felt that I was the one fate had spared. How guilty I felt that the best day of my life had been a trigger — we later discovered that a happy occasion (as well as a traumatic one) can trigger an episode. Amanda and I also feel guilty that we're powerless to prevent a suicide attempt when we know it's on the cards, and guilty that we're allowed to leave after visiting Rebecca or Irene in hospital.

And there's the loss. We grieve for the 'well' mother and sister we've lost. Amanda says: 'Bipolar disorder has undermined my relationship with my mum. I can't share my worries with her, not even if one of the kids has a cold, because an innocuous fact can become magnified in her mind, causing her mood to spiral out of control. So I tiptoe around her, saying, "We're all just fine".'

Amanda and I wanted to turn these decades of pain into something infinitely more positive, and so we began writing a book as a resource for our loved ones and others with bipolar. But as the book progressed, it gradually dawned on us that we were writing it for ourselves, too. We realised our genetic family tree means we have a much higher risk of developing the condition. So do our children.

At first this reality terrified us, but we came to realise that knowledge is power. We now know there are many ways to help prevent mental illness in those with a genetic susceptibility. And if our family is unlucky enough to be touched by bipolar disorder again, we know a diagnosis doesn’t rule out the possibility of a happy and fulfilling life.

Bipolar — the facts

• Anybody can suffer from bipolar disorder. In the UK, 2.4 million people have bipolar. Equal numbers of men and women are affected. The average age for diagnosis is 19, though as our family history shows (Rebecca was diagnosed at 22, Jim at 32, Irene at 51), there's no typical pattern. Genes count — an individual's risk increases the more family members who have it — but even those without any family history of the illness aren't immune, depending on a combination of upbringing, stress-load, hormones and the use of substances such as cannabis.

• The earlier the diagnosis, the better. Like diabetes, bipolar disorder is managed rather than cured. It's much easier to treat people who have had fewer than three episodes. After that, bipolar disorder gets incrementally more difficult to treat. If episodes are prevented — usually with a combination of medication, therapy and lifestyle choices — people can do extremely well.

• The shame is often harder to deal with than the symptoms. A recent report found that 70 per cent of people with mental health problems have experienced discrimination yet, just as diabetes is caused by an imbalance in blood sugar regulation, bipolar is caused by an imbalance in the brain's neuro-chemistry. There's no shame in having diabetes. Why the shame of bipolar? The only way the stigma can be erased is to be honest and open about the condition. Every time somebody says, 'I have bipolar', it's a nail in the coffin for ignorance, shame and stigma. A bipolar diagnosis doesn't define a person. Language conveys powerful meanings. Someone's not mad or a loony, they're ill. You wouldn't say 'John is cancer,' but 'John has cancer'. Likewise, don't say 'John is bipolar,' but 'John has bipolar'.

• Suicide is a risk. The suicide risk for someone with bipolar is about 60 times higher than the general population. Friends and family commonly experience guilt pangs after an attempt, but loving someone — however much — is not enough to rescue or save them. Notifying a health professional about any worrying behaviour is an option, as is passing on the number for The Samaritans (08457 90 90 90), a charity that provides confidential support 24/7.

• It's not all doom and gloom. A diagnosis of bipolar is linked to increased creativity and intelligence — think Stephen Fry. Plus, thanks to ongoing research, future treatment will be more tailored to an individual's symptoms. Compared with our parents' generation, the future is so much brighter for the one in 50 of our children who is destined to develop bipolar.

Resources

MDF The Bipolar Organisation runs self-help groups and provides information.

Bipolar Disorder — The Ultimate Guide by Sarah Owen and Amanda Saunders.