they either increase quality of life or decrease the rate of fracture incidence. OI affects only about one in 15,000 to 20,000 people, making it a rare genetic disease. Outcomes depend on the genetic cause of the disorder (its type). Type I (the least severe) is the most common, with other types comprising a minority of cases. Moderate-to-severe OI primarily affects mobility; if rodding surgery is performed during childhood, some of those with more severe types of OI may gain the ability to walk. The condition has been described since ancient history. The Latinate term osteogenesis imperfecta was coined by Dutch anatomist Willem Vrolik in 1849; translated literally, it means "imperfect bone formation". Signs and symptoms Orthopedic The main symptom of osteogenesis imperfecta is fragile, low mineral density bones; all types of OI have some bone involvement. In moderate and especially severe OI, the long bones may be bowed, sometimes extremely so. The weakness of the bones causes them to fracture easily; a study in Pakistan found an average of 5.8 fractures per year in untreated children. Fractures typically occur much less after puberty, but begin to increase again in women after menopause and in men between the ages of 60 and 80. Joint hypermobility is also a common sign of OI, thought to be because the affected genes are the same as those that cause some types of Ehlers–Danlos syndrome. Otologic By the age of 50, about 50% of adults with OI experience significant hearing loss, much earlier as compared to the general population. Hearing loss in OI may or may not be associated with visible deformities of the ossicles and inner ear. Hearing loss frequently begins during the second, third, and fourth decades of life, and may be conductive, sensorineural, or a combination of both ("mixed"). If hearing loss does not occur by age 50, it is significantly less likely to occur in the years afterwards. Mixed hearing loss is most common among those with OI of all age groups, while conductive hearing loss is most likely to affect older people, with sensorineural hearing loss most likely to affect children. Although relatively rare, OI-related hearing loss can also begin in childhood; in a study of forty-five children aged four to sixteen, two were found to be affected, aged 11 and 15. In a different 2008 study, the hearing of 41 people with OI was checked. The results showed