The London Marathon is always full of tales of courage and against-the-odds heroism.

But few of the runners in this year's race on April 17 will top the extraordinary story of a Norfolk woman.

For 75-year-old Daphne Hathaway is tackling the course despite having terminal bone marrow cancer - which has left her bones so brittle that she will have to walk the 26 miles and 385 yards.

To add a poignant twist to the tale, Mrs Hathaway is taking part to raise money for research into Alzheimer's, which has cruelly hit four of her close relatives in recent years.

The former newspaper sub-editor and secretary to the assistant director of RHS Wisley, lives at Threehammer Common, near Wroxham, with her husband Andy, who has battled Alzheimer's for a decade.

Mr Hathaway's mother Edith also had the condition, as did Mrs Hathaway's late mother, Lily Booth. And her father, 100-year-old Bill Booth from Wroxham, also has Alzheimer's.

The cause has given added impetus to Mrs Hathaway's training efforts, which have included walks of up to 22-and-a-half miles around the lanes of Norfolk.

She said: 'This cause is everything to me. I cannot imagine a worse disease for anyone to endure. And this is someone with cancer saying it.

'It affects everybody, and in the future there will be hardly a family without at least one member with Alzheimer's. I am so keen to raise its profile.'

Mrs Hathaway took up running in her late 50s, and has completed 14 marathons, including nine in London.

She was diagnosed with myeloma in March 2010, shortly before she was due to run that year's London Marathon. She deferred her place, even though she did not really expect to take it up.

She said: 'I'm training hard. I haven't got a car and I'm not allowed to cycle, so I walk everywhere - whatever the weather. I take a haversack with two filled bottles, sandwiches, a mac, my phone and �20 for a taxi, in case I can't carry on.

'I know I'm going to finish on the day, even though I think it will take me at least seven hours.

'I can't do it any quicker because the consultant has said I must have one foot on the floor at all times - and the people from the Alzheimer's Society want me to look out for people like Sue Barker with a microphone, so that I can talk about the cause.'

Mrs Hathaway said it would be her 'hardest challenge ever', and added that she was hoping to raise up to �3,000.

? To sponsor Mrs Hathaway, visit www.virginmoneygiving.com/DaphneHathaway or send a cheque to The Alzheimer's Society, Devon House, 58 St Katherine's Way, London E1 1JX, mentioning Mrs Hathaway.