Type IV OI is mostly defined in contrast to type III and type I, being the clinical classification for patients somewhere in the middle ground between the two. : 1511  As such, type IV OI is often termed "variable" OI,: 111  with the severity of even those in the same family (so, with the same genetic mutation) differing.Prepubertal bone fracture rates are another way of clinically assessing type IV OI—those with it tend to have fracture rates of ≈1 per year, compared to ≈3 per year for severe OI (type III).As in type I, some further split type IV into types IV–A and IV–B, defined again by the absence (IV–A) or presence (IV–B) of dentinogenesis imperfecta. : 217

Genetically defined types (types V–XXI)
As of 2020, fifteen types of OI are defined genetically:

Type V – Having the same clinical features as type IV, it can be clinically distinguished by observing a "mesh-like" appearance to a bone biopsy under a microscope. Type V can be further distinguished from other types of OI by the "V triad": an opaque band (visible on X-ray) adjacent to the growth plates; hypertrophic calluses (abnormally large masses of bony repair tissue) which form at fracture sites during the healing process; and calcification of the interosseous membrane of the forearm, which may make it difficult to turn the wrist. : 429   Other features of this condition may include pulled elbow, and, as in other types of OI, long bone bowing and hearing loss. Cases of this type are caused by mutations in the IFITM5 gene on chromosome 11p15.5.
: 161  The Norse king Ivar the Boneless, who lived c. 800 CE, is speculated to have had OI as well.Nicolas de Malebranche is oft credited as being the first person to describe the physical characteristics of OI in his 1688 book The Search after Truth, in which he describes a man who has had his "bones broken in the places a murderers would be" all his life. His confident description of the pathology of the disorder, however, which creates what he termed «enfants monstrueux» ("monstrous children"), is scientifically void—he wrote that it was due to the mothers antepartum viewership of a public execution by breaking wheel. : 683 : 165–168 The earliest modern scientific studies of OI began in 1788 by Olof Jakob Ekman, who described the condition, which he termed "osteomalacia congenital", in his doctoral thesis and mentioned cases of it going back to 1678, all in the same family, through three generations. Ekmans description of the condition mentioned dwarfism, bone fragility, and bowing of the long bones. : 763  In 1831, Edmund Axmann gave a detailed description of it in himself and his two brothers, being the first to mention blue sclerae as a characteristic sign of OI. : 683  Jean Lobstein first described the mild form of the condition, today known as type I, in 1833, calling it "osteopsathyrosis idiopathica". : 347 It was not until 1912 that hearing loss was positively recognized as a symptom of OI, first mentioned in a brief paper by the English physician Charles Allen Adair-Dighton.