Jamie Anderson watched helplessly as his father slowly succumbed to Alzheimer's. By the end, Gerry, the creator of Thunderbirds, could not even remember the name of his own hit television show, or that of his youngest son.
The junior Mr Anderson, 30, knew the odds of inheriting the same devastating genetic disease were against him, but decided that - for better or for worse - he had to know what they were.
After researching online he came across a DIY genetic testing kit that promised to give him the answer.
Using a sample of saliva, the test can map an individual's genome - the unique sequence of 23 pairs of chromosomes that make up our DNA - pinpointing the mutations that determine the likelihood of inheriting conditions such as Alzheimer's, Parkinson's, sickle cell anaemia, cystic fibrosis, as well as types of cancer.
The NZ$250 test, developed by 23andMe, the Silicon Valley biotechnology firm, can even look at genetic traits that predict whether you are likely to enjoy coffee, are predisposed to sneezing in bright light and your chances of going bald.
Almost a million people in America have taken the test since the company started in 2008, helping it become the largest private genomic testing company in the world. In December it launched in London and last week the testing kits arrived in Superdrug stores.
Genome testing has recently attracted public attention after Angelina Jolie, the actress, took a similar DNA test and found that, like her mother, she was a carrier of the high-risk breast and ovarian cancer gene BRCA1. With her chance of developing cancer put at 87 per cent, she decided to have a preventive double mastectomy and last month had her ovaries removed.
Referrals for breast cancer testing in the UK doubled after she went public.
But DNA testing is not without controversy. Some experts, including doctors and bioethicists, warn that the results are open to misinterpretation and that too much knowledge in a layman's hands can be dangerous. Others argue it is an individual's right to have access to their own genetic information.
Shortly after its launch, Time magazine named 23andMe's test the best invention of the year, describing it as one of the most crucial medical breakthroughs in decades. Five years later, in 2013, the Food and Drug Administration (FDA), America's health watchdog, became concerned about the accuracy of the results and banned the firm from offering customers interpretive reports alongside the raw data. It was also worried the tests would cause people to panic without seeking medical help.
Unlike the FDA, the Department of Health determined that the test was not a medical device, so it is not now subject to the same restrictions in the UK.
Mr Anderson, of Gloucestershire, was one of the first Britons to try it. He sent his saliva sample to the company's California laboratory and waited seven weeks for the results. "I wasn't sure if dementia ran in my family," he says. "All I knew was that my dad's mum might have had it, but it was never diagnosed as in those days she was just written off as a dotty old lady in a nursing home. I absolutely had to know how likely it was that this was to happen to me."
Mr Anderson said his father, a writer and director who also created the 60s programmes Stingray and Captain Scarlet and the Mysterons, started displaying symptoms as early as 2002, but was not officially diagnosed until 2011.
"By the last few months he didn't know who I was, he thought I was his big brother as I was bald and slightly taller than him. He was just so distressed by what he knew was going to happen to him," says Mr Anderson, who is a writer and television producer.
"Dad forged his entire career on his creativity, but the disease took every last bit of it away. By the end he was asking family members 'What was the name of that show I made?' It was the most unfair and cruel way for a mind like his to go." He died in 2012 - just 18 months after he was given his prognosis, at the age of 83.
Geneticists estimate that a person's chance of developing Alzheimer's disease is 60-80 per cent down to their genes.
"People always ask why I would want to know whether I'm likely to get a disease which has no cure, but there are so many lifestyle choices you can make to lower the risk that it's far from deterministic," Mr Anderson tells The Daily Telegraph.
Some studies have shown that people who exercise frequently and eat healthily are less likely to develop Alzheimer's, but the results are far from conclusive.
Mr Anderson's test results were more positive than he had expected, showing that he had a 60-65 per cent lower-than-average chance of developing dementia.
It is impossible to predict with 100 per cent accuracy if a person will go on to develop certain diseases as too many other factors are at play. But Mr Anderson still breathed a small sigh of relief. Mr Anderson, who in the same test found out he was at a slightly higher than average risk of developing stomach cancer, says it was "reassuring to know one way or the other".
He encourages family members of Alzheimer's sufferers to take the test, in the hope that larger sets of data will build a pattern, which will eventually help in finding a cure. Of the 900,000 people who have paid 23andMe to sequence their DNA, 80 per cent have agreed to allow their genetic information to be used for research, providing one of the world's largest databases of individual genetic information. The company was set up by Anne Wojcicki, whose husband Sergey Brin is the co-founder of Google. She has ambitious plans to process a billion people's DNA and sell the data to researchers to help discover new diseases and find cures for those we know about.
She has high-profile backing, both from Google and Yuri Milner, the Russian billionaire who has invested in Facebook, Twitter and the lodging website Airbnb.
Ms Wojcicki says: "I want the consumers to be in charge of what I think will be the next generation - personalised medicine." She believes people have a right to know about their genetic risks, so they can make informed lifestyle decisions.
Doctors and campaigners in the UK are concerned that the tests effectively remove medical professionals from the equation. "There is the danger of people receiving scary surprises without the presence of a doctor," says Dr Helen Wallace, of monitoring group GeneWatch UK. She added that the genetic testing market is "unregulated and much of the information people get is misleading or unreliable".
But Ms Wojcicki says: "I remember when pharmacy pregnancy tests were taboo. Within five to 10 years, taking an at-home DNA test will be as normal as buying groceries."