LONDON • Jonah Lomu was suffering from a rare and serious kidney disorder called nephrotic syndrome.
It was unclear yesterday whether the illness contributed to his death, with All Blacks doctor John Mayhew telling New Zealand's TV3 it was "totally unexpected".
But Lomu was on the waiting list for a second kidney transplant after the first transplant he received failed in 2011.
He revealed in 1995 that he had been diagnosed with the rare condition and in 2004 had a kidney transplant.
He managed to continue to play rugby throughout his illness, though he occasionally took time off for treatment.
About a quarter of nephrotic syndrome cases are caused by focal segmental glomerulosclerosis - scar tissue in the filtering unit of the kidney, called the glomerulus.
The causes of this scar tissue are often unknown, though known causes include infections, genetic problems, diabetes and sickle cell disease. The damage to the kidneys leads to an excess of proteins being removed in the urine and can increase the risk of infections and blood clots.
The outcome for patients varies, with some failing to respond to treatments and requiring dialysis or a kidney transplant. For others the syndrome is acute, but recovery is relatively swift. It can affect both adults and children.
In 2013, Lomu revealed he almost died in the hours after participating in the opening ceremony of the 2011 Rugby World Cup, with tests revealing the kidney he had received in 2004 was failing.
"My bloodstream was septic and the doctors were starting to think the worst - that my kidney had failed and my body was in total meltdown," he wrote in an updated version of his autobiography, Jonah: My Story.
"Over the next few hours I got worse. I couldn't keep anything down."
Lomu had been on the waiting list for a second transplant ever since, requiring dialysis three times a week for six hours a day. The chances of a body rejecting a second kidney transplant increases if the first transplant fails.
In an interview with the Daily Mail in August, Lomu said his goal was to live until 55 so that he would see both his children (with his third wife Nadene), Brayley, six, and Dhyreille, five, to the age of 21.