Supplementary Material for: Bathrocephaly and serpentine fibula as underrated features of Osteogenesis Imperfecta type I: a case report

Introduction: Osteogenesis imperfecta (OI) comprises a heterogeneous group of skeletal dysplasias characterized mainly by bone fragility and propensity to fractures. The most common forms include classic types I, II, III, and IV, according to the classification of Sillence, caused by variants in the COL1A1 or COL1A2 genes. This report describes a case series of patients with OI type I confirmed by whole genome sequencing, highlighting the clinical and radiological manifestations of one atypical family.
Case Presentation: Six individuals (1M:5F), aged 8 months to 34 years at their first consultation, were enrolled. All were clinically classified as OI type I due to the presence of osteopenia associated with blue sclerae and bone fractures; four presented with short stature, two with hearing loss, and one with fragile teeth; molecular testing confirmed that all presented with heterozygous pathogenic or likely-pathogenic variants in the COL1A1 gene. In one family, an unusual presentation was observed in the patient and her daughter, both of whom presented with severe short stature (Z-score < -6), abnormal skull shape (bathrocephaly), codfish vertebrae, bowing of the long bones in the lower limbs, and serpentine fibulas.
Conclusion: Bathrocephaly and serpentine fibula are rarely reported in classical OI types and are more frequently associated with other skeletal dysplasias, such as Hajdu-Cheney syndrome. This case report highlights the importance of recognizing underrated manifestations in OI and underscores the need for molecular confirmation.