Friendships forged at playgroup and cemented round the school gates last a lifetime. 

Like so many mums who meet this way, Barbara Dominy and Sue Foyle shared the ups and downs of their children's childhoods and marked the milestones together from first day at primary school to last day at secondary school, and all points in between. 

Then there were the birthdays from the early jelly and cake funfests through teenage sleepovers as Barbara's son Tom and Sue's daughter Charlotte progressed towards the landmark 18th and 21st birthdays. 

But Barbara won't be celebrating her son's 21st this year as she planned, because Tom - a fit and apparently healthy 20-year-old died suddenly in his sleep at his home in Salisbury last November.  He had been an active, easy going, young many, described by friends as the epitome of fitness and health with a passion for life. 

Losing a child is every parent's worst nightmare.  Barbara's friends watched as she, husband Mike and youngest son Jack struggled to cope with their terrible loss. 

It's devastating.  You just can't believe it - you don't want to believe it," says Sue.  "Because Tom was fit and healthy, it seems unbelievable.  "It wasn't a car accident, it wasn't a drug overdose, he was at home.  "He went to bed on Sunday night, Barbara came home from work on Monday, had her lunch, went upstairs and found him dead." 

Tom's death was attributed to Myocardial Fibrosis, which the family believe was virus-linked, and came just weeks after another family in Hale suffered a similar loss. 

In October, 17-year-old James Salisbury, a keen sportsman and talented swimmer and lifeguard, was found dead in bed by his mother when she went to wake him for school. 

James was studying for his AS levels at the Burgate School and Sixth Form Centre in Fordingbridge, which he had represented in football, cross-country, athletics, cricket and basketball. 

By tragic coincidence, Tom's brother Jack, 18 was also a sixth-former at the school and came home with the news. 

Sue recalls: "I was having coffee with Barbara at the time and she said there's nothing so horrible as losing a child and she wouldn't wish that on anybody, and lo and behold...." James had suffered from left ventricular hypertrophy, a rare undetected heart condition which causes the muscles surrounding the left ventricle of the heart to thicken causing irregular heart beat and subsequent heart failure. 

Sudden Arrhythmia or Adult Death Syndrome (SADS) is thought to account for the deaths of up to eight young, apparently healthy people under the age of 35 each week, according to the charity Cardiac Risk in the Young (CRY). 

As well as offering counselling and support for bereaved families, CRY is currently campaigning for ECG testing in schools to screen youngsters for potential problems. 

After Tom died, Sue wanted to do something positive to help and with Barbara's blessing, she applied for and was given a pledge place with CRY in this year's Flora London Marathon to run in Tom's memory.  With little experience in distance running beyond the annual 5km Race for Life, Sue, 50, started training in January with the support of friends, her husband and colleagues and children at Harnham Junior School where she is a finance and admin officer.  She had set herself a sponsorship target of £2,000 but had reckoned without Tom's popularity. 

By the time she set off on April 13 to pound the 26-miles of London's streets from Greenwich to the Mall, her sponsorship web page was already registering £3,700 and, at the last count, had passed £4,000. 

Through rain, hail and cold, Sue ran and trudged, covering the distance in five hours 41 minutes. 

"It's hard, she admits.  "The course itself is easier than you think, but it's the actual running - you get to the stage where it's too painful to run and it's too painful to walk but the crowd is willing you on and give you that extra spur. 

"It's an indescribable experience, just fantastic.  "You get carried along and you think 'I've got to keep going'.  "There was no way I was going to stop." 

Nursing aching muscles and sore feet, Sue said: "I saw Barbara this morning.  She's very pleased and proud and says I'm her hero but Barbara, Mike and Jack are the heroes for coping with losing Tom." 

Sue's daughter Charlotte said: "Running the marathon could not bring Tom back, but it provided those who loved and miss Tom with an outlet to share their support, grief and hope. 

"It also served as a reminder he will never be forgotten.  "For that, every mile was worth it." 

FACTS ON CARDIAC RISK IN THE YOUNG

Sudden Arrhythmia (or Adult) Death Syndrome is an umbrella term for the many different causes of cardiac arrest in young people.

The majority of young, sudden deaths are due to forms of heart muscle disorder and irregular heart beat.

Sport itself does not lead to heart attacks, but sporty youngsters are potentially most at risk because sporting activity puts most stress on the heart and could exacerbate an underlying but previously undetected cardiac abnormality. 

The charity Cardiac Risk in the Young aims to raise awareness of the condition, as well as [providing a counselling service for bereaved families and support for young people diagnosed at risk. 

The charity says that having an electrocardiogram (ECG) test is a simple way of spotting potential abnormalities. 

It is campaigning for the introduction of ECG testing in  schools and currently offers subsidised screening to you people between the ages of 14 and 35 through a number of clinics in the UK and mobile screening services. 

It recommends screening for anyone who has had a sudden death of a young person in the family or any young person suffering from exercise related chest pain, breathlessness, palpitations, dizziness or fainting. 

For more information, visit www.c-r-y.org.uk; www.sads.org.uk; www.cry-csc.org.uk; or contact the CRY office on 01737 363 222.