David Cameron spoke movingly about his son Ivan, who died in 2009 with a rare disease, when he opened a specialist research centre to revolutionise healthcare.
His six-year-old son Ivan suffered from Ohtahara syndrome, a rare form of epilepsy characterised by spasms.
The centre - named after one of the world's richest men, who was also present at the opening ceremony - aims to specialise in so-called "big data", which it says could help revolutionise health research into medical science's biggest enigmas. Its work is intended to offer patients better, safer and more personalised treatments.
In a speech to delegates, Mr Cameron said: "As I walked around the laboratory I met a young researcher, she said she was running genetic data - DNA tests - against a very unknown disease, a syndrome called Ohtahara syndrome, which is what my son Ivan suffered from.
"I will never forget when we were first told of the diagnosis of a desperately ill and disabled child. Then when you want to know more about it, there's very little that we know. It's one of the many parts of medical science where we have huge breakthroughs still to make."
The Prime Minister said he still received letters from across the country from people whose loved ones are diagnosed with Ohtahara.
He said: "It will be good to be able to write back to them and say there is, right here in Oxford, that vital piece of scientific work going on to try and link DNA information with this under-researched syndrome."
The centre is supported by a £20 million donation from the Li Ka-shing Foundation, as well as £10 million from the Government. It is being built in two phases and will house up to 600 scientists when complete.
The opening marked the completion of the first stage - a £35 million building on the university's Old Road Campus, which will be home to crucial research into disease.