A man found drowned in the sea was depressed because he was suffering from a serious genetic disorder.
Andrew Hoar had Huntington's disease, as did other members of his family, an inquest heard.
The symptoms of the disease include repetitive abnormal movements and psychiatric problems.
There is no cure and its complications mean sufferers rare
ly live for more than 20 years after diagnosis.
The inquest at Chester-le-Street Magistrates' Court heard Mr Hoar's brother died after contracting the disease and his sister is also a sufferer.
The body of Mr Hoar, 44, was found in the sea off Seaham's North Dock on April 17 at about 5.30am by a fisherman.
Mr Hoar's ex-partner, Marjorie Gleghorn, with whom he was still friendly, told the hearing: "He didn't seem very well in the days before.
"He kept saying over and over that he was 'losing it'.
"I had a good idea he might try to harm himself because he had tried twice before."
Mr Hoar spent the evening before his death at his home in Ivy Avenue, Deneside, Seaham, with his son and daughter.
Detective Sergeant Clifford Down, of Peterlee CID, told the inquest: "They were stopping in the house with him to keep his spirits up.
"I believe they played a family game with him and after they retired to bed, he got up sometime between midnight and about 5.30am.
"Mr Hoar was a regular dog walker in the area and the spot he was found is between half and three-quarters of a mile from his house, as the crow flies."
Det Sgt Down said there were no suspicious circumstances surrounding the drowning, and no note had been left by Mr Hoar.
North Durham coroner Andrew Tweddle said: "The Huntington's was causing
Mr Hoar increasing difficulties and we know he was depressed about that.
"As the coroner, I have to consider the possibility he intended to harm himself, but there is nothing to support that proposition.
"There was nothing untoward about the death, but exactly what led to it will remain a mystery. Only Mr Hoar knows what was going on his mind at the time."
Verdict: Open
