Gordon Brown's son has cystic fibrosisLast updated at 11:00 30 November 2006
Gordon and Sarah Brown with son John and baby Fraser
The Chancellor and his wife Sarah issued an upbeat message about fourmonthold Fraser's condition, describing him as 'fit and healthy'.
They told friends they did not want the announcement treated as a 'tragedy', and were confident medical advances would help him.
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But the show of optimism could not conceal the shock for a couple who suffered the devastating loss of their newborn daughter Jennifer Gordon and Sarah Brown with Fraser, right, and John in August
Jane from a brain haemorrhage in 2002. It is understood Fraser has a mild form of cystic fibrosis, an incurable condition which clogs up the lungs with mucus. He has been in and out of hospital in Edinburgh with minor chest infections, a symptom of the genetic disease.
Cystis fibrosis affects some 7,500 people in the UK. Despite medical advances in fighting the condition, the average life expectancy is still only in the mid-30s. A spokesman for Mr Brown said: 'Fraser is fit, healthy and making all the progress that you would expect any little boy to make.'
The Browns were told in July, soon after Fraser's birth, that he may have cystic fibrosis. Tests later confirmed it.
The spokesman said: 'Thousands of other parents are in the same position. They are confident that the advice and treatments available, including proper exercise and, later, sporting activity will keep him fit and healthy.
'The NHS is doing a great job, and Gordon and Sarah are very optimistic that the advances being made in medicine will help Fraser and many others.
'They hope to be able to play their part in doing what they can to help others.'
The Browns' other son, threeyearold John, is healthy.
Last night's news was in stark contrast to the scene four months ago when a beaming Chancellor emerged from Edinburgh Royal Infirmary, holding Fraser, and declared: 'I feel that the sun is shining very brightly on our family.'
But he took nearly ten weeks off before returning to Westminster in September. It now seems that his prolonged absence was at least partly due to the need for Mr Brown and his 45-year-old wife to cope with the discovery that their son was ill.
Last night's announcement, which stunned Westminster, comes as Mr Brown prepares to take over from Tony Blair.
It is likely to generate an outpouring of support for him.
The Chancellor has carried the burden of his son's condition in private at a time when he had to cope with both his own job and the pressure of preparing to become Prime Minister.
It could also mean that the leaders of the two main parties at the next general election will have physically handicapped children.
David Cameron's four-year-old son Ivan suffers from cerebral palsy and the demands of caring for him have strongly influenced the Tory leader's approach to politics.
Last night Yvette Cooper, the wife of Mr Brown's close ally Ed Balls, said that the Chancellor and his wife were feeling ' optimistic' about the future and that Fraser was developing well.
She said: 'This is the kind of thing that no parent wants to hear. But they are very optimistic. He is doing really well. He is strong and healthy.
'They are a very strong family. He is a delightful, bouncing boy. We saw him this week. He is a very bright and bubbly boy who is doing very well. Fraser is a lively addition to the family. They are getting on very well and it is great to see him developing so well.'
Miss Cooper added: 'Medical research goes in all sorts of leaps and bounds.'
Another friend of the Browns said: 'He's a beautiful baby. He is a joy to Sarah and Gordon.
'They just want the very best for him. They are facing this bravely and with determination. Whatever comes along, they will be strong as a family.'
Downing Street said Tony Blair would not be making a statement. A spokesman said it was a 'private' matter.
The birth of Fraser - christened James Fraser Vaughan - had been greeted by delighted family members as a second blessing after the tragedy of Jennifer's death.
Mr Brown's brother John said: 'The key thing was that the baby arrived safely, given what they have been through'.
Soon afterwards the couple issued a portrait showing a relaxed Mr Brown embracing his young family.
Jennifer Jane was born prematurely just after Christmas in 2001 and died in her parents' arms ten days later. The couple were visibly ravaged by her loss, but threw their efforts into setting up the Jennifer Brown Research Fund, which supports research to save newborn lives and solve pregnancy problems.
Mrs Brown has campaigned vigorously, gaining the support of high-profile figures including her friend JK Rowling.
Earlier this month, the Chancellor's wife announced she had edited a book of short stories by well-known authors to raise money for the charity.
The stories in Mums: A Celebration of Motherhood, were described as 'both touching and amusing'.