A 10-hour session led to problems

Dominic Patrick, 14, from Merseyside, developed deep vein thrombosis after a rainy day inside with a games console.

The potentially dangerous condition was caused because Dominic had his legs tucked under his body.

DVT is rare in younger people - it is mainly linked to long periods of immobility in older patients.

Cases arising among long-haul airline passengers led to the condition being dubbed "economy-class syndrome" - a reference to the lack of legroom perhaps helping it develop.

However, studies suggest that any situation in which someone spends hours sitting in one place - including at a desk in front of a screen - can increase the risk of a DVT.

The only risk factor we could find in this case was the fact that Dominic had sat on his legs for 10 hours playing computer games without moving Dr Russell Keenan, Alder Hey Children's Hospital

Dominic noticed something was wrong when, after getting up from playing games all day, he got pins and needles in his legs and one of his calves swelled up.

When this failed to go away, his father initially put it down to "growing pains", but eventually took him to a doctor, who diagnosed DVT.

Drug course

The 14-year-old was prescribed a long course of the blood thinning drug warfarin to prevent any recurrence.

His father told a newspaper: "This just proves that DVT can affect even the fittest and healthiest of children."

This is not the first time that computer games have been implicated in DVT formation.

In Thailand, the authorities proposed a curfew on online gaming between 10pm and 6am amid fears of both "addiction" to role-playing games, and the dangers of marathon sessions.

Mandatory play breaks every two hours were also proposed as a way of cutting the risk of DVTs.

Dr Russell Keenan, a paediatric haematologist from the Alder Hey Children's Hospital in Liverpool, said that it was extremely unusual to see DVTs in otherwise fit and healthy children.

He said: "I would expect to see a DVT in a child perhaps once every few weeks - but the vast majority of these involve children who are very seriously-ill in other ways.

"The only risk factor we could find in this case was the fact that Dominic had sat on his legs for 10 hours playing computer games without moving.

"If you fold the leg, you are basically folding the vein in the leg and causing the blood supply to stagnate. That is what might be causing the clot.