RÉSUMÉ
Osteogenesis imperfecta (OI) arises from a collagen type 1 defect due to several gene mutations, particularly COL1A1 and COL1A2. Its inheritance pattern is typically autosomal dominant, which is more common, or autosomal recessive, although sporadic cases also occur. Prenatal ultrasound can detect severe types, but genetic testing is necessary for confirmation, often at birth or in early childhood. We present a rare case of sporadic OI type III involving a three-year-old boy. Prenatal ultrasound initially revealed limb deformities and skeletal dysplasia, with subsequent confirmation at birth through bone deformities and multiple fractures. Exome sequencing confirmed the diagnosis at 15 months, revealing a new, rare variant in the COL1A2 gene. Pamidronate treatment began at seven months.