Known colloquially as OI or “brittle bone disease,” osteogenesis imperfecta is a genetic bone disorder that causes a person’s bones to break with little provocation. The condition develops due to a mutation in the collagen-producing gene (COL1A1 or COL1A2) in which collagen, the substance responsible for building and strengthening connective tissue between bones, is insufficiently produced in either quantity or quality. OI is genetic, developing in the womb; it is common for infants with OI to be born with broken bones. Due to the brittleness of their bones, people with OI often develop other chronic issues, such as muscle weakness, brittle teeth (dentinogenesis imperfecta), looseness of joints (joint laxity), and a crooked spine (scoliosis). Many people with OI also experience stunted growth due to bone breaks, and as a result, may be of short stature. 

Currently, OI is classified into several subtypes, each varying in severity. Olive’s OI in Hummingbird is considered mild, but it still impacts her life in significant ways. The most severe forms of the condition are fatal at, or shortly following, birth. Living with OI may cause emotional distress due to difficulties managing daily life; additionally, milder forms of the condition may not be visible to others, causing misunderstandings.