These approaches have led to the identification of new OI-causing genes and novel pathogenic variants that are not classically associated with collagen metabolism and can occur via distinct inheritance patterns, such as the first X-linked recessive form of OI (OI type XIX, OI19, MIM #301014), caused by missense mutations in MBTPS2 [3, 120, 121] (Fig. 3c, d). Here, MBTPS2 is linked to osteogenesis imperfecta.