Osteogenesis imperfecta type XVII: expansion of the phenotype

Biallelic variants in SPARC are extremely rare, and have been reported in only a few cases of autosomal recessive osteogenesis imperfecta (OI) type XVII. Here, we describe an individual with a SPARC homozygous missense variant (c.787G > A; p.Glu263Lys) and expand on the phenotype. The proband had a history of multiple fractures, osteopenia, severe thoracolumbar levoscoliosis, rib fusion, global hypotonia, conductive hearing loss, and was non-ambulatory. Several of his features were similar to previously described cases, such as early neuromuscular concerns, scoliosis, long bone and vertebral compression fractures, and delayed motor milestones, suggesting these are consistent across SPARC-related osteogenesis imperfecta (OI). However, the proband sustained fractures at a younger age with a more severe course compared to most previous reports. He also had bony fusion of several ribs and hearing loss, which have not been reported in SPARC-related OI. Overall, the proband supports the current phenotype of SPARC-related OI, but also expands the phenotypic variability.