Treatment Gives Dwarf Mice a Growth Spurt

The most common type of human Dwarfism results when cells in a child’s bones are overstimulated by growth factors. A mouse study, however, suggests that injecting such children with a molecular decoy that sponges up these factors could treat the condition.

People with the form of dwarfism called Achondroplasia (See picture below) rarely stand more than 1.5 meters tall. The mutation responsible for the condition ends up stunting the growth of the long bones in the arms and legs, bowing the vertebral column, and often constricting the passage through which the spinal cord runs.

A mouse that has the equivalent of achondroplasia  doesn’t measure up to an animal that received injections of FGFR3
Along with short stature, the condition can cause difficulty walking; fluid
buildup around the brain; and apnea, or the temporary inability to breathe.
Although researchers haven’t identified a treatment for achondroplasia, they have uncovered the molecular flaw that triggers it. As a typical child’s bones elongate, cartilage cells called chondrocytes mature and then die, allowing hard, bony material to supplant them. In children with achondroplasia, a genetic flaw causes a receptor on the surface of these chondrocytes to be hyperactive. When stimulated by molecules called Fibroblast Growth Factors, this receptor, known as FGFR3, Prevents the cells from maturing and Impedes bone formation.
Chondrocytes I
To calm this overzealous receptor, molecular biologist Elvire Gouze of INSERM in Nice, France, and colleagues resorted to deception. They repeatedly injected a solution of FGFR3 into mice that had a growth-hindering condition equivalent to achondroplasia.

The treatment restored normal growth in the mice and forestalled skeletal defects characteristic of achondroplasia, the researchers report online in Science Translational Medicine. Injections of the decoy cut the percentage of mice that showed abnormal curvature of the spine from 80% to as little as 6%, depending on the dose. When the treated mice matured, the females gave birth to normal numbers of pups, another sign that the skeleton—specifically, the pelvis—had reached full adult size.

FGFR3 injections benefitted the mice in another way, cutting their mortality rates by more than two-thirds. “We suppressed complications,” Gouze says. “They don’t have problems breathing, they don’t have paraplegia [inability to walk] anymore.” The team plans further studies on mice to confirm the approach’s safety and to nail down the optimal schedule for doses, she says.

“I think it’s a really exciting paper,” says clinical geneticist William Horton of the Shriners Hospital for Children in Portland, Oregon. “It clearly shows that if you give this agent, the bones grow.” 
Source: Sciencemag

Chondrocytes II