Fibrodysplasia Ossificans Progressiva: An Overview of "Stoneman Syndrome"
Olin, North Carolina
In biology class, your teacher might have told you that one type of tissue will never turn into another. The genes activated in each cell are only the ones needed for that cell type. For example, muscle or tendon will never turn into bone.
In most people, this is true. However, people with fibrodysplasia ossificans progressiva (FOP), colloquially known as stoneman syndrome, have a mutation that can lead to tissues, such as tendons, ligaments, and skeletal muscle, progressively turning into bone. FOP, first discovered in the eighteenth century, has fewer than one thousand documented cases, and has been estimated to have a prevalence of one in one million people worldwide.
The human body gets its different types of cells through a process called cellular differentiation. Through this process, a stem cell, a cell that has the ability to become multiple types of cells, undergoes changes to become a specialized cell, like a muscle cell or bone cell. One aspect of the cellular differentiation process is bone morphogenic protein (BMP) receptors. BMP receptors are present in some cells during the cellular differentiation process, and, when activated, transmit signals into the cell that determine what type of cell it will differentiate into. The primary function of BMP receptors in a person without FOP is to replace cartilage with bone through a process called ossification, as infants are born with cartilaginous bones that fuse together over time into adulthood.
The gene responsible for causing FOP is the ACVR1 gene, which encodes for type IA BMP receptors. When a mutation to the ACVR1 gene causes FOP, BMP receptors are activated when they typically would not be. This causes the receptors to carry out excessive signaling, leading to the growth of bone tissue in locations and circumstances under which it typically would not develop. There are multiple ACVR1 mutations known to cause FOP, but the most frequently observed one is the substitution of the amino acid arginine for histidine at position 206. The majority of documented FOP cases have been caused by sporadic mutations, but FOP is autosomal dominant, meaning that if one parent has the gene their child will inherit it. FOP is congenital, meaning that it is present from birth in affected individuals and cannot occur from a mutation later in life.
In people with FOP, BMP receptors can start signaling for the development of bone in response to minor soft tissue injury, such as a fall, penetration by a needle, or a viral infection. Bone development can even occur spontaneously with no clear trigger. The development of bone where it is not typically present is known as heterotopic ossification, and it can have major consequences for people living with FOP.
The fusion of joints, known as ankylosis, progressively limits mobility in people with FOP. The fusion of the bones in the legs makes walking difficult and eventually impossible, while fusion of the bones in the jaw can hinder a person’s ability to talk and eat, sometimes leading to malnutrition. When heterotopic ossification affects the ossicles, or bones of the ears, hearing loss is commonly observed. Additionally, affected individuals may experience swelling alongside the pooling of fluids in limbs as bone growths push against vessels and interfere with the pumping of blood. Entrapment neuropathies can be created when bone growths compress nerves, leading to extreme pain.
As bone tissue continues to grow, there can be less space in the thoracic cavity for the heart and lungs. As a result of this, cardiopulmonary issues, such as lung infections and heart failure, end up being the cause of death for many individuals with the condition.
FOP is strongly associated with a specific malformation of the big toes at birth, which has been present in nearly all documented cases. Other malformations have been known to be present in the fingers, spine, and legs. These malformations can indicate that an infant has the condition, giving caregivers an opportunity to learn about the condition and find ways to minimize its effects. While there currently is no cure, people with FOP typically live well into adulthood, and researchers continue to look for more effective treatments.
Works Cited:
Cellular Differentiation. (n.d.). Lumen Learning. Retrieved June 27, 2026, from https://courses.lumenlearning.com/suny-ap1/chapter/cellular-differentiation/
Fibrodysplasia ossificans progressiva. (2022, July 15). MedlinePlus. Retrieved April 4, 2026, from https://medlineplus.gov/genetics/condition/fibrodysplasia-ossificans-progressiva/
Fibrodysplasia ossificans progressiva (FOP). (n.d.). Penn Medicine. Retrieved April 4, 2026, from https://www.pennmedicine.org/conditions/fibrodysplasia-ossificans-progressiva
S. Kaplan, F., National Organization for Rare Disorders, The Perelman School of Medicine at The University of Pennsylvania, M. Shore, E., et al. (2024, June 26). Fibrodysplasia Ossificans Progressiva. National Organization for Rare Disorders. Retrieved April 4, 2026, from https://rarediseases.org/rare-diseases/fibrodysplasia-ossificans-progressiva/
Sanchez-Duffhues, G., Williams, E., Goumans, M.-J., Heldin, C.-H., & Ten Dijke, P. (2020). Bone morphogenetic protein receptors: Structure, function and targeting by selective small molecule kinase inhibitors. Bone, 138. https://doi.org/10.1016/j.bone.2020.115472
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