Milestone birthdays often provoke mixed emotions, but Dr Christian Jessen felt only a surge of relief when he celebrated his 30th.
Reaching that age, unscathed by ill health, he believed he had escaped a debilitating condition which he saw devastate the life of one of his closest relatives.
The TV doctor, best known for his medical advice on Channel Four's Embarrassing Bodies, grew up watching his uncle, Volker, battle multiple sclerosis (MS).
The condition affects nerves in the brain and spinal cord, causing a range of symptoms, including problems with movement, balance and vision. Worldwide, more than 2.3 million people (around 100,000 in the UK) are affected by MS and symptoms tend to appear when people are in their twenties and thirties, although it can develop at any age. It is two to three times more common in women than men.
"My father's brother, Volker, who was a vet, lived with MS for more than 25 years and was just under 30 when he was diagnosed, before I was born," recalls Jessen (38), who's supporting new website, 1MSg (one message), providing information and advice for MS patients.
"It's still not known what causes this condition, there may be a slight genetic link, although it's very low. It does seem to run in families, but the risk is small. My parents were worried about my developing it later in life, but were reassured by a specialist when I was a toddler that it wouldn't happen to me," he says.
"To be honest, I'm not actually sure how that doctor could have been so certain of that diagnosis, but that reassurance helped them at the time. As I grew up, though, I became conscious that fate can sometimes be cruel.
"I thought, 'Volker and I share similarities'. He trained to a high level as a vet and then was struck down, and there I was, following in his footsteps by entering the medical profession to graduate as a doctor.
"When my inner pessimist - medical students tend to think they've got every disease they learn about - nagged me, I'd occasionally succumb to a fleeting fear that it was almost bound to happen.
"So although people don't normally breathe a sigh of relief when they reach 30, I did, and as the years have gone by, I'm now pretty certain I won't be affected."
Volker suffered his first symptoms in his late twenties - shaky hands, a gradual loss of dexterity and periods of blurred vision.
He had the most common type, relapsing remitting MS, where symptoms come and go and, in remission, may improve or disappear. Those with primary progressive MS, which affects 10% of patients, have symptoms that get steadily worse and the onset of the disease tends to be later in life, in those in their forties or fifties.
"For my uncle, it must have been devastating to finally get such a diagnosis. In those days it meant premature death, whereas today, MS doesn't significantly shorten life expectancy. When he was diagnosed in the late Seventies, there were only steroids and other medications to relieve symptoms and latterly he suffered agonising muscle spasms and pain.
"Now treatments, particularly for relapsing remitting MS, aim to modulate the immune system so it's less likely to attack the central nervous system."
Although his uncle was forced to give up veterinary surgery, he continued as a travelling vet in a specially adapted car until his mid-thirties.
"Giving up his profession must have been a hammer blow. I know how devoted I am to my career and can only guess at the pain that must have caused him," says Christian.
"His MS often made him weak and as the disease progressed, it affected his speech so sometimes he could sound a bit slurry. He died aged 55 in 2003 when I was 25.
"Today, just because someone has MS it doesn't mean they can't lead a happy, healthy life."
By revealing his family's tragedy he aims is to raise awareness and encourage MS sufferers to have regular assessments.
"Latest figures show nearly a fifth of patients haven't seen a specialist for a year and yet those appointments are so key, so medication can be updated and, if necessary, more help, including therapies or support groups can be accessed," he says.
Christian has previously focused on a variety of issues, including a controversial Channel Four documentary in 2014, Cure Me, I'm Gay - he is gay and lives with his partner in London - as well as a health series about extreme eaters, Supersize vs Superskinny.
"I'd welcome a return of Embarrassing Bodies which was a groundbreaking show that over eight years changed the way we thought about health," he says.
"It was a victim of its own success and became rather over-exposed. It's popular worldwide so we may be looking at some international versions. Generally, awareness and knowledge of health can literally change people's lives and playing just a small part in that is a privilege."
Dr Christian Jessen is supporting a new website, 1MSg (one message), which gives information and advice to multiple sclerosis (MS) sufferers. The 1MSg campaign is supported by Biogen. Visit 1MSg.co.uk