By Fergus Walsh
Health correspondent, BBC News
Claudia has passed the 'faulty gene' on to some of her children
Claudia Sanford and her children know all too well about how genetics can affect your health.
Thirty years ago, Claudia's brother dropped dead while playing basketball. He was just 21.
A few years ago Claudia began having heart palpitations.
Eventually a genetic test determined that the condition was a rare inherited heart disorder - arrhythmogenic right ventricular cardiomyopathy (ARVC).
Claudia already knows she has passed the condition on to at least one of her three children. Her son Chris tested positive, while one of her daughters is negative.
"It's been difficult knowing that I have this gene and have passed it on," says Claudia.
"But hopefully genetic testing - knowing about the disease - will prevent what happened to my brother happening to me or my children".
Her son, Chris Carnes, is 27. For him the major concern is whether he has now passed the faulty gene on to the next generation.
"I would like to get my son James tested, and the chance that he may have it plays on my mind more than anything else."
On medical advice Claudia has give up long-distance running because of the potential strain on her heart, while Chris no longer plays basketball.
Claudia's third child, Stephanie Carnes, initially declined a test but has finally made up her mind to go ahead.
"It's taken a little over a year to come to that decision for several reasons.
I do want to have kids, and if I am positive then I'd want to have them tested so that I could do what's best for them
"One was the uncertainty about the disease, because there is still a lot we don't know about it and sometimes the advice from doctors is contradictory.
"Another was whether it would affect my health insurance and I might not be covered if I tested positive."
I met Claudia, Stephanie and Chris at the University of California Medical Center in San Francisco, which has a dedicated genetic testing department. Stephanie has not had to make her decision alone.
She has talked through the issues with Colleen Brown, one of the genetic counsellors.
The test itself is simple. Stephanie uses a large cotton bud to wipe some cells from the inside of her cheek, and these are sent off to a lab.
She knows she has a 50:50 chance of inheriting the faulty gene but simply having this does not automatically mean she will get AVRC.
"I've definitely had to think about what I will do if I test positive", says Stephanie.
Stephanie will begin law school this autumn and eventually wants to have children.
She says the thought of passing on the condition, made her want to know her own status.
"I do want to have kids, and if I am positive then I'd want to have them tested so that I could do what's best for them".
The genetic testing experience of Claudia and her children is a world away from the sort of online DNA profiles on offer.
Dr Robert Nussbaum heads the division of medical genetics at the University of California.
He says: "There are many families where genes play a major factor in their health and we need to look after them and ensure they are properly counselled.
But the democratisation of genetics through online testing, while it has some value in spreading an interest in genetics and raising excitement, I don't think it's going to have the big impact on healthcare."