My mother's family carries a gene for an exotic eye shape. My sister has it; her eyes are almond shaped, tip-tilted; "faerie eyes" as a rather romantically inclined boyfriend once called them.

It skipped my mother and it skipped me, but it's come out in my eldest daughter. We've no idea where it comes from, but's it's interesting to look back in the family and try to find out.

In my father's family it's lungs. We were at my Uncle's 70th birthday party yesterday, celebrating the amazing fact that he has actually reached 70, while he sat, constantly short of breath, with his oxygen cylinder at his side. Little Max, at two, was running around the garden playing, but has just had a four day stay in hospital with his asthma. There ensued much discussion about who in the family has the lungs, how many times they have had pneumonia and who's escaped.

And then there's the other thing in my father's family. That's the illness we don't talk about. My father died from it. I've nearly died from it (twice). My sister has had a bout or two of it and it's hit at least one cousin (that I know of). The Victorians didn't seem to have the taboo that we do – they called it "Melancholia" and seemed to accept that some people were affected by it while others escaped.

But I can't be the only parent who anxiously watches their children for signs that they have inherited this melancholic gene. With two academic, ambitious, high-achieving girls, my concern is surely valid.

I try not to let it be a forbidden subject. We talk about when "Mummy is poorly" and how we manage it in the family. We talk about the importance of talking about how we're feeling and that sometimes those feelings might be a sign that we are really poorly and we might need some medicine.

Forewarned is forearmed and I want my girls to know what's happening if it ever does. I also want them to know that it is just the same as getting the lungs, the eyes, the milk allergy; it's genetic and it can be managed.

And it might not happen. But I'm going to stay vigilant – just in case.