JK Rowling has been a long-term supporter of the MS charity
JK Rowling has stood down as patron of the Multiple Sclerosis Society Scotland claiming that the charity is being split by an internal row.
The Harry Potter author, whose mother had the disease and died aged 45, has backed the charity for nearly a decade.
But she said conflict between Scotland and management in London had resulted in resignations and demoralisation.
An MS Society spokesman said it was undergoing a governance review and regretted Ms Rowling's departure.
Ms Rowling said in a statement: "I have now reluctantly decided that I cannot, in good conscience, continue to be the public face of a charity that is changing beyond recognition from the one with which I have been so proud to be associated."
JK Rowling speaks in a rare interview about her mother's death after suffering MS
She said she had taken the decision to stand down "with profound sadness and regret" but added that her financial support of a research project at Edinburgh University would continue.
She added: "I also remain committed to financing future research into the treatment and causes of multiple sclerosis, and to campaigning for better care and treatment of people with MS in Scotland, which is the MS capital of the world.
"I have not taken the decision to quit my position as patron of MSSS lightly. Late last year I initiated and attended a mediation session, in the hope of sorting out long-standing and escalating conflict between the Scottish council and management in London, driven by the imposition of changes by London.
"Unfortunately, this achieved very little. With mounting frustration and disappointment, I have witnessed resignations of immensely dedicated people within MSSS and the increasing demoralisation of staff whom I have come to know and admire over the 10 years of our association."
We would have preferred to do this [review] with JK Rowling's involvement, but we appreciate that significant change can be difficult
MS Society spokesman
She said her disappointment could not be overstated and expressed hope that the MS Society Scotland manages to resolve its difficulties.
In 2006, Ms Rowling gave a "major" undisclosed cash donation to help set up a multiple sclerosis research centre in Edinburgh.
An MS Society spokesman said they were sorry JK Rowling was stepping down after being a great patron for many years.
He said: "The society is in the middle of a governance review to make sure we are properly organised to build on the excellent work we already do in Scotland and across the UK.
"We are a strong, democratic organisation and this review is being done in consultation with all of our 43,000 members.
"We would have preferred to do this with JK Rowling's involvement, but we appreciate that significant change can be difficult."
He urged supporters of the MS Society to work with them to deliver the best possible support to more than 10,000 people living with MS in Scotland.
Scotland is believed to have the highest rates of multiple sclerosis in the world.
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