Gordon Brown insists today he remains upbeat about his baby son Fraser’s future after revealing that his third-born has cystic fibrosis.
The Chancellor and his wife Sarah were told their younger son might have the condition shortly after his birth in July.
A spokesman for Mr Brown said that despite confirmation of the diagnosis Fraser was "fit, healthy and making all the progress that you would expect any little boy to make".
"Thousands of other parents are in the same position," the spokesman added. "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 him and many others, and they hope to be able to play their part in doing what they can to help others."
Political friends and rivals alike sent their best wishes to the Chancellor, with Tory leader David Cameron among the first to offer his support.
Mr Cameron’s son Ivan, born in 2001, is disabled by a rare condition that combines epilepsy and cerebral palsy.
Mr Cameron has previously spoken of going into "mourning" when doctors gave him and wife Sam the news.
The Tory leader said: "Sam and I are thinking of Gordon and Sarah and their family at this time and we send them our best wishes for the future."
Housing minister Yvette Cooper, a close friend of the Browns, along with her husband Economic Secretary Ed Balls, said they were a "strong and happy family".
She said: "Fraser’s a lovely, bouncy healthy little boy. He’s doing really well. This is the kind of thing that no parent obviously wants to hear, and it was the same for Gordon and Sarah in the summer.
"But they’re very optimistic and doing really well and medical advances obviously happen all the time."
Mr Brown and his wife were hit by tragedy in January 2002 when their first child, daughter Jennifer Jane, died just 10 days after her premature birth.
But the couple were overjoyed in 2003 with the birth of their oldest son John and the family grew again in July of this year with the birth of James Fraser, weighing 7lb 14oz.
Asked about the earlier tragedy, Ms Cooper told Sky News: "I think obviously this is very different, Fraser is a lovely part of their family and they are all enjoying life and getting on with things, he’s doing very well, this is a very different situation now."
Cystic fibrosis (CF) is a life-threatening inherited genetic disease which disrupts the way the digestive and respiratory systems work.
It affects five babies born each week in the UK, and more than 7,500 babies, children and young adults are living with the condition. Average life expectancy is early 30s.
Testing of infants for CF is already routine in Scotland, Ireland, Wales and parts of England, and the Government plans to introduce screening programmes for all newborn babies throughout the UK.
Ed Owen is a board member of the Cystic Fibrosis Trust, and knows Mr Brown through his former job as an adviser to leader of the Commons Jack Straw.
Mr Owen told the Press Association he had spoken to the Chancellor and could empathise with what the couple were going through because his four-year-old daughter had the condition.
"Children with cystic fibrosis do have to undergo a daily regime of medication and therapy, but given the extraordinary development in treatments over recent years children can expect to live an extremely happy, active and in most ways normal life."
Mr Owen said Mr Brown had helped raise funds for the condition before Fraser was born.
"He was always very supportive of the trust and two years ago hosted a reception at Number 11. He made a speech and has been very supportive of efforts to raise funds.
"It’s something that he personally had been aware of through the charity work that he has been doing."
Shadow chancellor George Osborne offered support to his counterpart, saying: "My thoughts and best wishes go to Gordon and Sarah and their family at this difficult time."
The Chancellor is understood to be at 11 Downing Street with his family last night.