Reported by Julielynn Wong, MD

A single gene may shed light on why more than half of transplanted kidneys fail in 10 years, a new study found.

The study of nearly 4,500 European transplant recipients, some whom were followed for 20 years, found kidneys with one version of the gene were 69 percent more likely to fail, sending patients back to dialysis and a transplant waiting list.

But with a wait list 74,000 names long and only 17,500 kidneys donated annually, doctors won't be excluding any organs based on the gene variant just yet.

"We just don't have enough donor kidneys to go around now," said Dr. Michael E. Shapiro, associate professor of surgery at New Jersey Medical School/University of Medicine and Dentistry New Jersey, who was not involved in the study. "So we couldn't exclude such kidneys based solely on genetic variation."

The study authors are unsure why the gene variant is linked to a higher risk of kidney failure after a transplant, but they suspect it might have to do with the anti-rejection drugs needed to prevent the immune system from attacking the new organ. Those drugs can cause kidney failure if they accumulate in high levels, they said.

But because kidneys are such a rare and valuable resource, even those more likely to fail in the long run will continue to be transplanted. The alternative is dialysis, a process that artificially filters blood, according to Dr. Stanley Jordan, medical director of the Kidney Transplant Program at Cedars-Sinai Medical Center in Los Angeles, who was not involved with the study.

And dialysis has its drawbacks.

"We know that remaining on dialysis has a very high mortality rate, as high as 20 percent per year for some patients," said Jordan.

Dialysis costs roughly $85,000 per year, compared with $19,000 per year for a working transplanted kidney, Jordan said, citing a 2011 report on the United States Renal Data System website. But the cost of treating a failed kidney transplant can be as high as $230,000 in the first year, with Medicare usually bearing the brunt of these costs, he added.

In the future, a screening test to identify a number of genes could help doctors find the best approach to dealing with patients who receive kidneys that are at higher risk for failure, according to the study authors.

"Studies such as this give cause for optimism that, in due course, an understanding of the genetics of kidney transplantation can lead to better risk prediction and to the development of therapeutics," he said.

In the meantime, kidney transplant patients will continue to soldier on.

"It may not be in all patients' best interests - or even possible - to wait for the 'perfect' kidney, as this might not come up in a reasonable time frame if the patient needs transplantation urgently," said study senior author Dr. Richard Borrows, nephrologist consultant at the department of nephrology and kidney transplantation at the University Hospital Birmingham, Queen Elizabeth Hospital, in the U.K. "Under these circumstances it is appropriate to offer transplantation, even if the kidney may not be perfect, as it will still improve the quality of life, and hopefully life span."