Bent bone dysplasia syndrome
Rare skeletal dysplasia with bowed bones and often lethal outcome.
Bent bone dysplasia syndrome (BBDS) is a very rare genetic disorder that affects the skeleton, marked by curved long bones and poor bone mineralization. The best-known type, linked to the FGFR2 gene, tends to be severe and often leads to death before birth or shortly after. Two genetic forms exist: type 1, caused by changes in FGFR2, and type 2, caused by changes in both copies of LAMA5.
Signs of the condition may be spotted before birth, when ultrasound shows bowing of the long bones, particularly the thigh bones. Other possible features include a poorly formed skull, early fusion of skull bones, small or oddly shaped collarbones, abnormal finger bones, excess body hair, and problems with the liver or urinary and reproductive organs. While the disorder is usually fatal around the time of birth, a few individuals have lived longer.
Diagnosis relies on a combination of physical and X-ray findings, often confirmed by genetic testing. Before birth, ultrasound or fetal X-rays can reveal bone bowing and other skeletal issues; after birth, a full skeletal X-ray series and gene sequencing for skeletal dysplasia genes may be used.
Most reported cases end in death before birth, as a newborn, or in early infancy. In one early study of several cases, three children survived longer, but all needed breathing support. A later report described a child living into early childhood, showing that the FGFR2 form is not always fatal, though serious complications remain common. The oldest known person with BBDS, a 4-year-old boy with the FGFR2 type, was still alive as of 2026, making developmental progress and able to walk and interact.
- classification
- Genetic skeletal dysplasia
- genetic forms
- FGFR2-related (type 1) and LAMA5-related (type 2)
- typical prognosis
- Perinatal lethal; longer-term survival reported in a small number of individuals
- oldest documented survivor
- 4-year-old male (FGFR2 type), living as of 2026
- key features
- Bowed long bones, poor skull mineralization, craniosynostosis, distinctive craniofacial findings
Lore & Background
Bent bone dysplasia syndrome may be suspected prenatally when imaging shows bowing of the long bones, especially the femora. Other findings can include a poorly mineralized calvarium, craniosynostosis, small or unusually shaped clavicles, abnormal phalanges, hirsutism, hepatic abnormalities, and genitourinary abnormalities. The condition is usually described as perinatal lethal, but longer-term survival has been reported in a small number of individuals.
Reader's Guide
Bent bone dysplasia syndrome represents a rare but instructive example of genetic skeletal disease, highlighting the critical roles of fibroblast growth factor receptor 2 and laminin subunit alpha 5 in bone development. Its significance lies in the severe, often lethal presentation that nonetheless shows a spectrum of outcomes, including rare longer-term survival. The oldest documented individual, a 4-year-old male with the FGFR2 type, demonstrates that the condition is not invariably lethal, though severe complications remain common. The syndrome underscores the importance of prenatal imaging and molecular genetic testing for diagnosis. Its inclusion in reference compendia aids clinicians in recognizing and differentiating it from other skeletal dysplasias such as campomelic dysplasia and Raine syndrome. The existence of two genetic forms (FGFR2 and LAMA5) points to genetic heterogeneity and the need for precise molecular diagnosis to guide counseling and management.
Did You Know?
- The most studied form, FGFR2-related bent bone dysplasia, is usually severe and often lethal before or shortly after birth.
- Two genetic forms have been described: type 1 associated with FGFR2 and type 2 linked to biallelic variants in LAMA5.
- The oldest documented individual with BBDS is a 4-year-old male (FGFR2 type), still living as of 2026 and able to walk and interact.
- Reported symptoms include poor mineralization of the skull, craniosynostosis, osteopenia, hypoplastic clavicles, and distinctive craniofacial findings such as low-set ears and natal teeth.
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