A father of two has to keep his mobile phone permanently on vibrating alert - because the ring tone could kill him.

Call centre recruitment team leader Jon Cotterill-Bolsover has one of the rarest genetic heart conditions in Western Europe. 

any unexpected loud noise such as his phone ringing or a sudden shock could stop his heart beating. 

Mr Cotterill-Bolsover, 28, suffers from Brugada Syndrome, a rare disorder that disrupts the heart's normal rhythm and was only identified in the 1980's. 

He said: "The danger with mobile phones for someone with my condition is that the ringing can scare you and send the heart into an abnormal rhythm. 

"It is safer to keep the phone on vibrate only or silent mode.  It is just not worth the risk if my heart stops for the sake of a phone call. 

"I also use my phone as an alarm clock in the morning but ensure it plays a slow piano tune which builds up gradually.  That way it cuts out any potential problems." 

Mr Cotterill-Bolsover, who has a pregnant fiancé Katrina and daughters Natalia, five, and Anastasia, four, is most fearful of quiet rooms. 

He said: "When I'm at work or in a crowd on the streets there is noise all around so a phone ringing would not be a problem. 

"But it could cause a shock if I was in a quiet room and someone's mobile rang.  It is out of my control, all I can do is try and keep calm." 

Mr Cotterill-Bolsover, from Darfield, Barnsley is one of the few sufferers who know they have the condition - most die before it is diagnosed.  Undiagnosed heart conditions, usually labelled under the umbrella Sudden Unexpected Death Syndrome (SUDS), kill eight under-35s every week in Britain. 

The former martial arts competitor only found out about his condition by chance when he contracted a kidney infection last August. 

Doctors detected an irregular heart beat but were baffled as to the cause.  It was only when he was referred to specialists at Sheffield's Northern General Hospital that the disorder was confirmed. 

It restricts the movement of sodium ions into the body cells.  There are no physical signs but the genetic defect causes an abnormal heart rhythm that can lead to blackouts, palpitations or sudden death. 

To control his condition, he was fitted with an Implantable Cardiac Defibrillator last November.  The unit shocks the heart if it stops and improves the odds of survival by more than 90 per cent. 

He said: "In a way it was fortunate.  I had the kidney infection otherwise my condition may never have been discovered before it was too late. 

"One of the doctors at Barnsley District Hospital had just returned from a SUDS conference and suspected I had Brugada Syndrome so I was sent for further tests in Sheffield which confirmed the diagnosis." 

Before such equipment was developed, sufferers had little life expectancy beyond 30.  Now his is busy planning for his wedding to Katrina next month and hopes to form a SUDS support in the Barnsley area. 

The founder and chief executive of the charity Cardiac Risk in the Young, Alison Cox, said: "In a way Jon is one of the lucky ones.  Many young people simply don't find out about their heart conditions and sadly die. 

"We are hoping to introduce a national screening programme and we believe any young person who is worried about their heart of has a history of sudden death in their family should be screened."