The family of a teenage brother and sister who died in almost identical swimming pool tragedies has called for greater awareness of a rare heart condition thought to have caused their deaths.

Daniel and Anne-Marie Readshaw were both 13 when they collapsed and died without warning two years apart.

An inquest held yesterday into Daniel's death revealed they are both likely to have died of a rare heart defect which could have been triggered whilst swimming.

No specific tests for the condition were carried out when Anne-Marie died in the pool at Spennymoor leisure centre in 2001.

But following Daniel's death during a swimming session at St John's RC School, in Bishop Auckland, last December a detailed investigation identified the probable cause as Long QT Syndrome.

In a separate tragedy the children's parents Iain and Marie, of Ferryhill, County Durham, lost another daughter, ten-year-old Catherine, to leukaemia in June.

Two other children, Nicole, 12, and Rachel, seven, have been tested for the defect and scans have cleared them of the condition. Pathologist Dr Nigel Cooper said the condition, possibly hereditary, can lie dormant for years until a specific trigger such as cold water or loud noises causes heart failure.

He said: "Daniel would have felt no pain, he would have lost consciousness straight away and not been aware of what was going on."

The inquest, at Bishop Auckland, heard that teacher Keri Lowes tried to resuscitate Daniel but he could not be saved and that inspectors from the Health and Safety Executive had no major safety concerns about the school.

Grandfather Joe Conroy said that GPs and families need to know about the condition so youngsters who show signs of heart complaints can be tested.

He said: "It may be uncommon but we've had two cases in one household and know of another in the neighbourhood so it isn't that rare.

"It is something people have to be made aware of, so any parent concerned about a child who faints or blacks-out can ask that they be tested regularly.

"GPs also need to me be more aware of it, in America it is a routine test for schoolchildren.

"We had a warning with Anne-Marie but were told three times she fainted because she was teenage girl, if this condition had been checked I'm convinced Daniel would still be here."

Dad Iain Readshaw said the family had been comforted by the support of people in Ferryhill and Spennymoor, which has included fund-raising to send them for a break together in Portugal.

He said: "Without support from local people we would not have been able to do this."

Despite being a rare condition, there have been several high profile LQTS related deaths including that of footballers Miklos Feher, of Hungary, Cameroon international Marc-Vivien Foe and Terry Yorath's teenage son Daniel.

Former James Bond actor Sir Roger Moore was fitted with a pacemaker when he discovered he had the condition after passing out during a stage performance.

Eve Knight, service development officer from the British Cardiac Patients Association, said: "Where a problem is found in a family that might be genetic we would want to see more screening of brothers, sisters and other relations.

"This is not the first time that families have been affected in this way. I know of a family where the daughter and then the father died. Only at that point was the son screened.

The Department of Health is currently drawing up new guidelines for the management of patients with heart rhythm problems.