Jonah Lomu
Jonah Lomu suffered from rare kidney disease nephrotic syndromeReuters

New Zealand rugby union player Jonah Lomu has died at the age of 40 in Auckland. His death was described as "totally unexpected" and details of the cause of death are yet to be announced.

However, Lomu had been living with a rare kidney condition for almost 20 years, having been diagnosed with nephrotic syndrome in 1996. He continued to play rugby after his diagnosis, occasionally taking time off for treatment.

He retired from rugby in 2007, three years after receiving a kidney transplant and in 2013 he announced he had almost died after the opening ceremony of the 2011 Rugby World Cup when doctors found the kidney was failing.

Since then he had reportedly been on a waiting list for a second kidney transplant and had been receiving dialysis thrice a week for up to six hours at a time. Dialysis eliminates waste of unwanted water from the blood artificially – normally the kidneys do this naturally.

What is nephrotic syndrome?

Nephrotic syndrome is normally diagnosed in children, although it can affect people of any age. It is rare, affecting around three in every 100,000 people. Those with the condition have kidneys that do not work properly, resulting in large amounts of protein leaking into their urine. This loss of protein causes a range of problems, including the swelling of body tissues and increasing the risk of catching infections.

Nephrotic syndrome can be caused by a number of kidney problems or other conditions, including lupus, diabetes and sickle cell anaemia. There is also a form of the syndrome called minimal change disease, the cause of which is unknown. Congenital nephrotic syndrome is normally caused by an inherited faulty gene.

Swelling symptoms result from the low level of protein in the blood reducing the movement of water surrounding tissues back into the blood vessels. This is normally first seen around the eyes and lower legs. Infections are caused due to the loss of antibodies in the blood that help fight off infections. Another problem can be blood clots because of the loss of proteins that help prevent this.

The condition is normally managed with steroids to stop protein from leaking into the urine. Diuretics can also be prescribed to help reduce the build-up of fluid, while penicillin is prescribed during relapses to reduce the risk of infection.

However, sufferers of congenital nephrotic syndrome, may be given albumin infusions – most of the protein lost in nephrotic syndrome is albumin. This involves adding albumin to the blood over a few hours. In some cases, doctors will also recommend kidney transplantation, which stops the proteins being lost – but can result in rejection – and being on dialysis while waiting for a suitable donor.