New type of rare brittle-bone disease discovered

Between 300 and 400 people in Switzerland and around half a million worldwide suffer from brittle-bone disease, which causes their bones to break like glass. Not only is their bone formation insuffi-cient; other body tissues containing connective tissue are also affected.

Cecilia Giunta and Marianne Rohrbach, both researchers from the Children’s Research Center at the University Children’s Hospital Zurich, their teams and colleagues from the USA and Thailand have now detected a new type of brit-tle-bone disease, identifying two families with a total of eight patients in all.

The patients suffer from heightened bone fragility, bone deformities and stunted growth. In both families, this new form of oste-ogenesis imperfecta was caused by two different mutations of the same gene (MBTPS2) in the X chromosome. The disease is inherited in an X-chromosome-recessive manner and affects men and boys as only they carry a copy of the X chromosome.

Simple test in the urine

“Exactly how common the newly discovered disease is remains unclear,” says Cecilia Giunta. “That said, it’s easy to identify other patients, as we demonstrated that the disease can be diagnosed with a simple measurement of biomarkers in the urine.”

These biomarkers indicate changes in the crosslink-ing between the structural proteins in the bone. MBTPS2 encodes a protease, i.e. a protein, which is able to cut and therefore activate other proteins – so-called transcription factors. These activated pro-teins bind to the DNA and regulate genes involved in the bone and sterol metabolism and the regula-tion of cell stress.

This was primarily shown in zebra fish in 2003. Shortly afterwards, researchers dis-covered that IFAP syndrome, a group of rare dermatological diseases in humans, is caused by muta-tions in MBTPS2.

“Surprisingly, mutations in the gene MBTPS2 also cause a completely different disease, namely oste-ogenesis imperfecta,” explains Marianne Rohrbach. The culprit is a change in the bone metabolism, which no longer seems to be impaired in the case of dermatological diseases.

Exactly how and why mutations can trigger two completely different diseases in the same gene remains unclear. The team headed by Cecilia Giunta and Marianne Rohrbach are now focusing their research on finding the an-swer. The scientists hope to gain new insights into bone developments and sterol metabolism, which could one day mean improved treatment options for patients.

Literature:
Uschi Lindert, Wayne Cabral, Surasawadee Ausavarat, Siraprapa Tongkobpetch, Katja Ludin, Aileen Barnes, Patra Yeetong, MaryAnn Weis, Birgit Krabichler, Chalurmpon Srichomthong, Elena Makaree-va, Andreas Janecke, Sergey Leikin, Benno Röthlisberger, Marianne Rohrbach, Ingo Kennerknecht, David Eyre, Kanya Suphapeetiporn, Cecilia Giunta, Joan Marini, and Vorasuk Shotelersuk. MBTPS2 mutations cause defective regulated intramembrane proteolysis in X-linked osteogenesis imperfecta. Nature Communications. DOI: 10.1038/NCOMMS11920

Contacts:
Dr. sc. nat. Cecilia Giunta
Division of Metabolic Diseases,
Children’s Research Center, Children’s Hospital Zurich
Phone: +41 266 73 10
E-mail: cecilia.giunta@kispi.uzh.ch

PD, Dr. med. et phil. nat. Marianne Rohrbach
Division of Metabolic Diseases,
Children’s Research Center, Children’s Hospital Zurich
Phone: +41 266 73 10
E-mail: marianne.rohrbach@kispi.uzh.ch