Mystery surrounds how a man died from sporadic Creutzfeld-Jakob Disease(CJD) just six months after he had a kidney operation, an inquest has heard.
Brian Edwards, 62, from Newtown, Powys died in May, 2007 after surgery at the Royal Shrewsbury Hospital to unblock arteries leading to his kidneys.
The Welshpool inquest heard soon after leaving hospital Mr Edwards started acting oddly and suffered memory loss.
Powys Coroner Peter Maddox recorded a verdict of death by natural causes.
In a letter read out in court from the CJD surveillance unit at Edinburgh University, it said father-of-two Mr Edwards had the sporadic form of CJD, which accounted for 75% of CJD cases in the UK.
But as Mr Edwards had not received a blood transfusion during his kidney operation, the surveillance unit was unable to identify how he had contracted the disease.
Addressing Mr Edwards' family Mr Maddox said: "I don't know what caused it (the CJD). The expert evidence I have is that there is no known cause for this.
"Sorry I can't provide you with the answer which is obviously very important to you."
A post mortem examination revealed Mr Edwards had died from aspiration pneumonia caused by CJD.
In a statement, Mr Edwards' partner of 11 years, Sheila Davies, said after he was discharged from hospital on 23 December 2006, he was tired and his mannerisms had changed.
She said in the weeks that followed he began acting oddly and had problems with his memory.
But she said his GP had put it down to depression.
The inquest heard Mr Edwards had worked at the Institute of Grassland and Environmental Research IGER) near Aberystwyth between 1983 and 1998.