A mother who gave her brain-damaged son a lethal heroin injection in order to end his "living hell" has lost her appeal against conviction.
Frances Inglis, 57, of Dagenham, Essex, had denied murdering Thomas Inglis, 22, on 21 November 2008 but was jailed for life with a minimum term of nine years.
Three Court of Appeal judges rejected her conviction challenge but reduced her minimum prison term to five years.
Her barrister told them she believed her son was in "constant pain".
Inglis was found guilty of murder and attempted murder by a jury at the Old Bailey in January this year.
Mr Inglis had suffered severe head injuries when he fell out of a moving ambulance in July 2007.
His mother first tried to end his life two months after the accident when he was being treated at Queens Hospital in Romford, Essex.
His heart stopped for six minutes but he was revived.
She was charged with attempted murder before successfully ending his life in November 2008, after barricading herself in her son's room at the Gardens nursing home in Sawbridgeworth, Hertfordshire.
Lord Judge said of the concept of mercy killing: "We must underline that the law of murder does not distinguish between murder committed for malevolent reasons and murder motivated by familial love.
"Subject to well-established partial defences, like provocation or diminished responsibility, mercy killing is murder."
At the appeal hearing, Inglis's QC Alan Newman said she feared her son would die in agony and gave him the injection to end his life "peacefully and painlessly".
Mr Newman said: "She was entirely taken up with the belief that Tom was suffering and that he was trapped in a sort of living hell and in pain."
Lord Judge said the evidence showed Inglis had not lost self control and had applied her mind to her objective, "which was to kill her son".
The judges ruled that her appeal against conviction was "not arguable".
Lord Judge said: "The fact is that he was alive, a person in being. However brief the time left for him, that life could not lawfully be extinguished.
"Similarly, however disabled Thomas might have been, a disabled life, even a life lived at the extremes of disability, is not one jot less precious than the life of an able-bodied person.
"Thomas's condition made him especially vulnerable, and for that among other reasons, whether or not he might have died within a few months anyway, his life was protected by the law, and no one, not even his mother, could lawfully step in and bring it to a premature conclusion."