Osteogenesis Imperfecta: Fragile Bones

Osteogenesis imperfecta (OI), which translates to ‘bones formed imperfectly’, is a rare genetic condition that causes bones to be fragile.

Due to its rarity, healthcare professionals may have limited awareness, understanding and experience when caring for individuals with this condition (The OI Society of Australia 2019; Palomo et al. 2015).

Types of Osteogenesis Imperfecta

There are five main types of OI ranging from mild to severe, with the mildest form of OI also being the most common. There are also many subgroups of these types.

Type 1 OI is the mildest form of OI, and may not be diagnosed until later in life, whereas the more severe types of OI can cause infant death during or shortly after birth, often as a result of respiratory failure.

The 5 types of OI can be classified as follows:

OI Type I: non-deforming OI with blue sclerae

• This is the mildest form of OI and is characterised by increased bone fragility, blue sclerae and increased susceptibility to hearing loss.

OI Type II: Perinatally lethal OI syndromes

• This is the most severe and deadly type of OI. It is often detected at 18 to 20 weeks gestation, and sadly, babies with this type of OI will rarely survive.

OI Type III: Progressively deforming OI

• OI will be present in these individuals from birth with bone fragility and multiple fractures leading to a progressive deformity of their skeleton. In the past, many individuals with this type of OI didn't survive into adulthood due to complications of skeletal chest wall deformity causing pulmonary hypertension, cardio-respiratory failure and kyphoscoliosis. However, with current therapeutic options, these individuals are now surviving into adulthood.

OI Type IV: Common variable OI with normal sclerae

• These patients have recurrent fractures, osteoporosis and deformity of both the long bones and spine, but will have normal sclerae by the time they reach late childhood.

OI Type V: OI with calcification in interosseous membranes

• This type of OI is indicated by moderate to severe bone fragility with progressive calcification of the inter-osseous membranes in the forearm and legs.

(The OI Society of Australia 2019; Van Dijk & Sillence 2014)

The severity grading of each type relies on assessing the individual’s clinical data, historical data, frequency of fractures, bone density and level of mobility. Statistically, however, approximately only 7 people per 100,000 people are born with any type of OI (The OI Society of Australia 2019; US National Library of Medicine 2018; Van Dijk & Sillence 2014).

Causes of Osteogenesis Imperfecta

OI is caused by a mutation in one of the two genes that produce collagen. It causes the person to have either a decreased amount of collagen or poorer quality collagen, which then causes their bones to be weak and consequently fracture more easily.

The mutated gene can be inherited from one or both parents or can be the result of a new and random mutation. It's important to note that parents of a child with OI often will not display OI themselves (The OI Society of Australia 2019; Van Dijk & Sillence 2014).

Diagnosing Osteogenesis Imperfecta

Diagnosis occurs as a result of investigations being undertaken due to a child experiencing frequent fractures. As well as frequent fractures, OI may be diagnosed through clinical signs and tests such as:

• Blue sclerae: note that this is not present in all types of OI
• Opalescent teeth: not present in all types of OI
• Family history: however, in many cases of OI, there will be no family history of OI
• Blood tests: these include calcium, phosphorus and serum alkaline phosphate. Blood tests are important in order to exclude other causes
• Urine tests: these allow determination of the level of bone breakdown and turnover occurring
• X-rays: many OI patients will have Wormian bones, which are extra bones present in the skull
• Bone density scans
• Genetic testing:uncommon, due to the cost and how time-consuming these tests can be.

(The OI Society of Australia 2019)

How Does Osteogenesis Imperfecta Present?

People with OI will often be of short stature, have blue-tinted sclerae, some form of hearing loss, brittle teeth, muscle weakness, hypermobility and potentially progressive skeletal deformity and restricted breathing.

Many people will also be diagnosed with osteoporosis. There may also be cardiovascular effects related to OI, which are usually reported in adults rather than children. These could include forms of valve dysfunction and aortic root dilation.

Another implication for adults over 40 years of age with OI is that more than 50% of sufferers will also have some form of hearing impairment. Experiences of vertigo are also quite common (The OI Society of Australia 2019; Palomo et al. 2015; Van Dijk & Sillence 2014).

Care for individuals with OI should take into account not only connective tissue and bone deformities but also the consequential effects of the condition, such as vertigo.

Pain is also often present in individuals with OI and when uncontrolled, can negatively impact the individual’s quality of life.

It's important to note that the symptoms of OI may differ between types. There are many common variables between the types, although some symptoms are more common in certain types of OI than others.

Therefore, if you are caring for someone with OI, it's important to determine which type of OI they have and what symptoms they are experiencing (MedlinePlus 2020; Van Dijk &; Sillence 2014).

Treating Osteogenesis Imperfecta

As a genetic condition, OI will often affect many of the body systems and cannot be cured. Therefore, treatment aims to manage some of the associated signs and symptoms.

One of these treatments includes intravenous bisphosphonate therapy to help treat bone fragility, increase bone density and decrease the fracture rates of the long bones in children with OI (Palomo et al. 2015; MedlinePlus 2020).

The implementation of management strategies for individuals with OI is also an important part of treatment. Therefore, the healthcare professional’s role needs to not only focus on assisting with treatment strategies but also management strategies in areas such as pain, mobility, hearing impairment and any modifications to maintain the individual's quality of life.

Additional Resources

• An Overview of Osteoporosis | Ausmed Article

References

• Medline Plus 2020, Osteogenesis Imperfecta, US National Library of Medicine, viewed 24 January 2022, https://ghr.nlm.nih.gov/condition/osteogenesis-imperfecta
• The OI Society of Australia 2019, What is OI, Osteogenesis Imperfecta Society of Australia, viewed 24 January 2019, https://www.oiaustralia.org.au/about-oi/
• Palomo, T, Fassier, F, Ouellet, J, Sato, A, Montpetit, K, Glorieux, F H & Rauch, F 2015, ‘Intravenous Bisphosphonate Therapy of Young Children With Osteogenesis Imperfecta: Skeletal Findings During Follow Up Throughout the Growing Years’, Journal of Bone and Mineral Research, vol. 30, no. 12, viewed 24 January 2019, https://onlinelibrary.wiley.com/doi/full/10.1002/jbmr.2567
• Van Dijk, F S & Sillence, D O 2014, ‘Osteogenesis Imperfecta: Clinical Diagnosis, Nomenclature and Severity Assessment’, American Journal of Medical Genetics, vol. 164, no. 6, viewed 24 January 2019, https://onlinelibrary.wiley.com/doi/full/10.1002/ajmg.a.36545