Previously, we compared the molecular features of OI and IFAP/KFSD caused by pathogenic missense variants in MBTPS2 (hereafter termed MBTPS2-OI and MBTPS2-IFAP/KFSD, respectively) by RNA-sequencing-based transcriptome profiling of control and patient-derived primary fibroblasts (14). The gene discussed is MBTPS2; the disease is osteogenesis imperfecta.