'Dripping Candle Wax' Bone Disease: Scientists Find Cause of Rare Condition That Causes Bones to 'Flow'

Melted candles in Isla Vista, California, May 25, 2014. A new study has revealed why some people's bones "drip" like candle wax. David McNew/Getty Images

A new study has shed rare light on the cause of a condition dubbed "dripping candle wax" bone disease, linking it to a genetic mutation.

Formally known as melorheostosis, the genetic condition is characterized by the thickening of the dense outer layer of the bone. On X-rays, the affected bones resemble a candle with wax flowing down its sides. According to the National Institutes of Health (NIH), only around 400 people worldwide have been diagnosed with the disease.

The benign condition affects the development of soft tissue. It can therefore impact a person's functions, causing limb, hand and foot deformities as well as chronic pain.

An x-ray image of a patient with melorheostosis shows excess bone formation, likened to dripping candle wax. National Institutes of Health

"Most adults have the problem of weakening bones as they grow older. These patients have the opposite problem as some of their bones are rock hard and still growing," Dr. Timothy Bhattacharyya, head of the Clinical and Investigative Orthopedics Surgery Unit at the National Institute on Arthritis and Musculoskeletal and Skin Diseases at NIH and co-senior author of the study said in a statement.

A team at the NIAMS and the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) worked on the study published in Nature Communications on Wednesday. They hope their research will help to develop treatments for the rare condition, as well as offer insight into more common bone problems such as osteoporosis and fractures.

With the help of 15 volunteer melorheostosis patients from around the world, researchers were able to investigate whether genetic mutations only occur in the affected bone tissue: those which resemble a melted candle. Scientists tested samples from biopsies on the participants' healthy and "dripping" bones, and checked for differences in the part of their genetic coding related to proteins.

Of the 15 participants, eight had mutations in the MAP2K1 gene—which creates the MEK1 protein—in the affected bone, but not the healthy one. Previous studies have linked MAP2K1 to conditions including cancer, as well as diseases where the blood vessels in the head and neck grow abnormally.

"Scientists previously assumed that the genetic mutations responsible for melorheostosis occurred in all cells of a person with the disorder," said Dr. Bhattacharyya. "Our team hypothesized that mutations might only occur in the affected bone tissue."

"This is an exciting study of a very rare bone disorder that not only identified the responsible mutation in half of the patients, but uncovered fundamental information about the role of a cancer-related gene in the metabolic pathways of normal bone," senior co-study author Dr Joan Marini, of NICHD, added in a statement. He said that the having the patients onboard "really changed the scientific landscape on this topic."