Political correspondent, BBC News
David Cameron said his experience of life with Ivan has shaped his policies
For most politicians, the personal and the political are closely intertwined. Human experience forms the basis of the ideas which go on to become policy.
In David Cameron's case, the life and now, tragically, the death, of his son Ivan goes to the heart of who the Conservative leader is as a politician.
Mr Cameron's friends speak of a man whose life was changed after the birth of his son.
No-one would deny that David and Samantha Cameron come from anything other than extremely privileged backgrounds.
But Ivan's condition, Ohtahara Syndrome, meant that a comfortable lifestyle had to take second place to the needs of their son.
That meant late-night visits to the hospital, sometimes sleeping on the floor by their son's bedside.
It meant meeting other parents with seriously ill children, from all social backgrounds and walks of life.
But perhaps most importantly in terms of David Cameron the politician, it meant a profound respect and admiration for the NHS.
Conservative leaders have sometimes had a problem convincing the public the National Health Service would be safe in their hands.
From the outset, David Cameron has made clear the important part he believes it plays in the life of the nation - based on the significant part it plays in his own life.
He told the Tory Party conference in 2006: "For me, it's not a question of saying the NHS is safe in my hands.
"My family is so often in the hands of the NHS. And I want them to be safe there. Tony Blair once explained his priority in three words: education, education, education. I can do it in three letters - NHS."
But as well as the praise for those at the sharp end of the NHS - the nurses, doctors and carers, there is sometimes an anger as well - anger at what David Cameron sees as the bureaucracy which exists in the system - but also anger at its failures to provide the services which families in a far worse position than his own require.
Should David Cameron win the next election, his experience of life with Ivan won't necessarily make him a good prime minister.
But it will inform his views - and behind nearly every decision he makes, whatever happens in his political life, a little bit of Ivan will be there.