The patients’ average boost in height to about 6 centimeters (2.4 inches) per year is close to growth rates among children of average stature, and the side effects of the drug were mostly mild, according to the researchers.
An increase in the annual growth rate alone may have a positive effect on some patients’ quality of life. For other patients, now and in the future, our hope is that the altered bone growth throughout the body could ease such problems as sleep apnea, neurological and leg and back problems, and improve their quality of life,” says Julie Hoover-Fong, M.D., Ph.D., associate professor and director of the Greenberg Center for Skeletal Dysplasias at the Johns Hopkins McKusick-Nathans Institute of Genetic Medicine. “Right now, the results of the study show an impact on growth, and this effect is sustained, at least over nearly four years in this trial. The potential long-term benefit will take more time to observe.”
Achondroplasia, although rare, is the most common form of dwarfism worldwide, affecting an estimated 1 in 15,000-40,000 live births. The condition is caused by mutations in a gene called FGFR3 that result in the excess production of proteins that slow bone growth. The disorder is marked by disproportionate short stature with shortened limbs, near normal-sized torsos and enlarged heads.
About 20% of people with achondroplasia inherit the mutations, meaning most children born with it have parents of average height. People with achondroplasia are prone to develop sleep apnea, chronic ear infections, neurological problems, spinal stenosis and bowed legs, frequently requiring surgical treatments to relieve pain and other symptoms.
There are no treatments able to reverse achondroplasia or treat the genetic culprit itself. However, growth hormone has been approved to treat the condition in Japan and occasionally is used off label elsewhere, but is not considered very effective in achondroplasia.
Vosoritide is a synthetic version of a protein present in humans called C-type natriuretic peptide. It is designed to bind to a specific receptor on the surface of chondrocytes, a type of cartilage cell found in the growth plates of bones. Once joined, the vosoritide-receptor connection sends a signal inside the fibroblast to stanch the flow of negative growth factors that were triggered by the mutation in the FGFR3 gene.
“This is the first therapeutic option that targets the molecular cause of the condition,” says Hoover-Fong.
For the currently reported study, conducted between January 2014 and July 2018, investigators enrolled 35 children ages 5-14 and followed them for a midpoint of 42 months. There were 19 girls and 16 boys, including two Hispanics, seven Asians and two African Americans.