By Emma Wilkinson
Health reporter, BBC News
Paget's disease causes painful deformities
Three genes which account for 70% of cases of a painful bone condition have been identified by Scottish scientists.
It is hoped the finding could lead to a screening test for Paget's disease, which affects up to one million people in the UK, Nature Genetics reported.
The genes are thought to regulate bone repair and may explain why the bones of people with the condition become enlarged and malformed.
Screening could help doctors target preventive treatment at an early stage.
The international team led by researchers at the University of Edinburgh studied the DNA of 1,250 patients with Paget's disease to pinpoint the genes that cause the condition.
It showed three genes that were faulty more frequently in patients with the bone disease than in healthy people.
Together they account for seven in ten cases, they said.
The findings explain why many patients with Paget's disease have a family history of the condition.
A screening test for the genes could allow early detection of the disease and enable doctors to give preventative treatment before bones have become damaged.
It adds to another gene which had already been found in 10% of cases.
In healthy people old bone is broken down and replaced with new cells as part of the normal cycle.
But this regeneration goes into overdrive in Paget's disease and patients suffer from bone pain, brittle bones susceptible to fractures, and advanced arthritis.
Researcher Dr Omar Albagha said the findings were a "major advance" in understanding why and how the disease develops.
"The three genes identified from this study contribute to 70% of the disease risk - quite unusual in common diseases.
"We are currently extending our studies to identify the genes responsible for the remaining 20% of the disease risk."
Professor Stuart Ralston, who led the project at the University of Edinburgh, said the effects of the genes were so powerful, a screening test was a real possibility.
"This is important since we know that if treatment is left too late, then irreversible damage to the bones can occur.
"If we were able to intervene at an early stage with preventative therapy, guided by genetic profiling, this would be a major advance."
There is a trial underway at Edinburgh University to determine if Paget's disease can be prevented in people with a genetic predisposition to the condition with a drug which inhibits the breakdown of bone.
Marilyn McCallum, chief executive of the Paget's Association, said the research was a "very exciting development".
"This project makes genetic testing a real possibility," she said.
A spokesman for Arthritis Research UK which funded a large part of the research said: "We're hopeful this work will ultimately have a direct impact on patient care."