The Sun are claiming a world exclusive saying it's another family tragedy for Gordon Brown and his wife Sarah, following the loss of their first daughter Jennifer five years ago.
The Sun carries a beautiful informal family picture on their website and comments:
The awful tragedy means that the next general election could be fought by two leaders with physically handicapped children.Tory leader David Cameron's four-year-old son Ivan has cerebral palsy.
Cystic Fibrosis is the UK's most common life-threatening, inherited disease and affects more than 7,500 babies, children and young adults.
Average life expectancy is currently just 31.
The Press Association are tonight quoting a spokesman for the Chancellor and his wife, who went through personal tragedy in 2000 when their first daughter Jennifer died within days of her birth. A trust was set up in her memory.
The spokesman said tonight:
"While Gordon and Sarah's younger son, Fraser, has been diagnosed with cystic fibrosis, he is fit, healthy and making all the progress that you would expect any little boy to make.UPDATE: BBC Political Editor Nick Robinson tells how Gordon Brown was visibly moved a couple of years ago when he hosted a fundraising event for the Cystic Fibrosis Trust at 11 Downing Street.
"They were told in late July that Fraser may have cystic fibrosis. Tests since then have confirmed this.
"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 him and many others, and they hope to be able to play their part in doing what they can to help others."
Robinson says he stopped filming to give the Chancellor privacy after he was visibly moved at meeting a beautiful charismatic young woman ill with cystic fibrosis who was waiting for a lung transplant "because time is running out".
Robinson says there is real hope that a gene therapy cure will be developed. He points pout that not long ago cystic fibrosis was a disease only children had. Now half its sufferers are adults, he says.