Fibrous dysplasia (FD) is a genetic condition in which normal bone tissue is gradually replaced by abnormal fibrous tissue. The bone in the affected area becomes weaker and can expand, deform, or cause pain.
The cause is a mutation in the GNAS gene, which occurs spontaneously during early embryonic development. In the vast majority of cases, FD is not inherited - parents do not pass it to their children. The mutation is somatic, meaning it affects only some cells in the body (mosaicism).
FD may affect a single bone or many. It can run quietly without symptoms for years, or cause serious deformities and hormonal problems. Every case is different - which is why correct diagnosis and individualized treatment matter.
Educational content, not a substitute for a medical consultation. Before any clinical decision, please consult a clinician experienced with FD/MAS.
The most common form - affects a single bone. About 70% of cases. Often discovered incidentally on imaging ordered for another reason. Can involve the skull, maxilla, mandible, ribs, or femur.
Affects two or more bones - often on one side of the body. Symptoms appear earlier than in the monostotic form, usually in childhood. May lead to body asymmetry, pathological fractures, and walking difficulties.
The most severe form: polyostotic FD combined with hormonal disorders (precocious puberty, hyperthyroidism, excess cortisol) and café-au-lait skin pigmentation. MAS requires multidisciplinary care - endocrinologist, orthopedist, and other specialists.
FD symptoms depend on the location and extent of lesions. Not every patient feels pain - many learn of the disease incidentally.
Most common symptoms:
In children, FD often becomes apparent between ages 3 and 15, when bones grow intensively. After skeletal maturity, disease activity usually stabilizes.
FD is estimated to affect 1 in 5,000 to 10,000 people. This means 3,800 to 7,600 people in Poland may have it. Yet most clinicians will never encounter an FD patient. The clinical picture is sometimes mistaken for bone tumors, leading to unnecessary surgeries - especially in children.
If a bone lesion is suspected in you or your child, ask your doctor about the GNAS gene mutation test. It is a genetic test that unambiguously confirms or excludes fibrous dysplasia. Histopathology (biopsy alone) may not be enough.
Diagnostic path →