A brother and sister who died in identical swimming pool accidents two years apart may both have suffered a rare heart defect which can be triggered by water and loud noise.

Daniel and Anne-Marie Readshaw were both 13 when they collapsed and died with no warning whilst swimming with pals.

Their shattered family - who have also lost another of their five children to leukaemia - believed it was a terrible coincidence.

But an inquest into Daniel's death yesterday discovered they are both likely to have been killed by a condition called Long QT Syndrome.

Their family called for greater awareness of the illness and more stringent checks for heart defects in children.

Daniel died in December last year during a supervised swimming lesson with 24 other pupils at his school.

Two years earlier his sister Anne-Marie, also 13, died in a leisure centre swimming pool.

To compound the misery of their family, sister Catherine died aged 10 in June after a three and a half year battle with leukaemia. The family said the death of her older brother and sister had a devastating effect on her ailing health. It has been established Daniel died from Long QT. An inquest into Anne-Marie's death left an open verdict, however doctors are now linking her death with Daniel's and believe she also suffered the same condition.

Pathologist Dr Nigel Cooper told an inquest in Bishop Auckland, Co Durham, that the condition affects less than 100 cases in the UK.

Long QT syndrome (LQTS) causes an abnormality of the heart's electrical system.

Though the mechanical function of the heart is entirely normal, the electrical problem is due to defects in heart muscle cell structures called ion channels.

The electrical defects predispose sufferers to a very fast heart rhythm called arrhythmia or "Torsade de Pointes" (TdP), which leads to sudden loss of consciousness and may cause sudden cardiac death.

A loud noise or contact with water can cause the condition to come into play.

There are instances of children collapsing while being loudly scolded by parents or teachers. Dr Cooper said: "This is a very rare heart condition which can be triggered by loud noise or water.

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

Daniel's teacher from St John's Primary School in Bishop Auckland, Karri Lowes, broke down as she gave evidence.

She said: "Two other children were at the side of the pool and Daniel was beside them. They did not say anything. I was asking them what was wrong with Daniel, he was over the edge of the pool with his head on his arm.

"I just dragged him straight out onto the side of the pool and started to talk to him saying "Daniel, can you hear me?"

"There wasn't any real response from Daniel and when I felt he was giving me no response I started giving him CPR."

She said she then called paramedics.

As Miss Lowes left the dock, Daniel's grandparents Kath and Joe Conroy stood up to hug her.

Fiona MacNeel, principal inspector of safety for County Durham, said the safety plan at the swimming pool at St John's School was in place and had been put into action.

South Durham coroner Andrew Tweddle said: "Daniel's death is absolutely tragic and because of the death of his sister has attracted a lot of interest.

"But in this case Daniel and his sister have died in extremely similar circumstances making the situation even more prominent.

"The pool was not deficient in any way but for this family to lose two children in this way and three children within three years is just about unimaginable.

"I would think that if anything good has come out of this it is that Daniel's death has raised the question of health in other members of the family.

"I agree with the pathologist that Daniel's death was one natural causes."

Speaking after the inquest for the family Joe Conroy, 61, said: "The verdict was expect really we had seen post mortem reports a few weeks ago.

"The only thing that this brings out is that all doctors should look more into this problem.

"If a child has a black out they should be taken straight to their GP and they should be given an ECG test. It may be nothing but they may have the same thing as Daniel.

"On Anne-Marie's headstone we will write "a tear she had, a smile she shared" because she was so dear to us like Daniel."

Nicole, 12, and Rachel, seven, are now the only surviving children of Ian Readshaw, 38, and wife Marie, 33.

Marie could not bear to be at the hearing but Ian, a communications worker, said: "My kids still go swimming so they are not frightened of water, they have had all the tests already and they are okay.

"So we are happy to take them to the swimming pool.

"This has been devastating for us, especially with the loss of Catherine after her fight with leukaemia.

"Nicole was so devastated, she was very close to all her brothers and sisters."

Magistrates imposed a £20,000 maximum fine on Sedgefield District Council after hearing only one lifeguard was on duty at the time of Anne-Marie's death.

The 13-year-old drowned in 2001 despite the efforts of her friend Sarah Cornbill to save her at Spennymoor Leisure Centre, Co Durham.