Osteogenesis imperfecta (all types)

Overview

Osteogenesis Imperfecta (OI) encompasses a range of genetic disorders primarily affecting connective tissue, leading to bones that are unusually fragile and prone to breaking. It is often known as 'brittle bone disease'. This condition is not caused by calcium deficiency or poor diet, but rather by underlying genetic changes that impact the body's ability to produce strong, healthy collagen, a key protein in bone structure [PMID:33604313].

OI can manifest with varying degrees of severity, from very mild forms where individuals experience only a few fractures throughout their lifetime, to extremely severe forms that can be life-threatening around the time of birth. Beyond bone fragility, OI can also affect other parts of the body, including teeth, hearing, and the whites of the eyes (sclera). The exact prevalence of OI is estimated to be around 1 in 15,000-20,000 individuals [PMID:33604313].

Because of its variable nature, understanding OI involves recognising that it is not a single condition but a spectrum of related disorders. Clinical classification systems exist to help categorise the different types, primarily based on symptoms and genetic findings. However, the unifying feature across all types is the fundamental defect in collagen production or processing.

Symptoms & clinical features

The primary and most defining symptom of Osteogenesis Imperfecta is bone fragility, leading to fractures from minor trauma or, in severe cases, without any apparent cause. The number and severity of fractures can differ significantly between individuals, even within the same family or type of OI. Some individuals may experience hundreds of fractures over their lifetime, while others may have only a handful [PMID:27091845].

Beyond bone fractures, other clinical features commonly associated with OI include blue or greyish tint to the whites of the eyes (sclera), which is due to the thinness of the sclera allowing the underlying blood vessels to show through. Hearing loss, often developing in adulthood, is another frequent symptom. Dental problems, such as dentinogenesis imperfecta (brittle, discoloured teeth prone to chipping), can also occur. Short stature is common, particularly in more severe forms of OI, due to the cumulative effect of multiple fractures and spinal compressions.

Additional features can include bone deformities, curvature of the spine (scoliosis), loose joints, and muscle weakness. The breathing difficulties sometimes seen in severe OI types can be due to chest wall deformities. The constellation of symptoms helps clinicians classify the type of OI and guide management strategies.

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Affected organs

Osteogenesis Imperfecta primarily affects the skeletal system, leading to fragile bones, recurrent fractures, and bone deformities. This includes the long bones of the arms and legs, the spine, and the ribs. The impact on the skeleton can result in short stature, bowing of limbs, and scoliosis (curvature of the spine).

Beyond the bones, other organs and tissues rich in type I collagen are also often affected. This includes the eyes, where the sclera (the white part of the eye) may appear blue or grey. The ears can be affected, leading to progressive hearing loss, typically conductive or mixed, which often begins in young adulthood. Teeth can also be impacted, presenting as dentinogenesis imperfecta, characterised by discoloured, translucent, and brittle teeth. Ligaments and tendons may also be more lax, contributing to joint hypermobility.

Multiple body systems

Systemic involvement

Cellular impact

Mechanism at cellular level

Risks & severity

The severity of Osteogenesis Imperfecta varies significantly, ranging from very mild to perinatal lethal forms. In mild forms, individuals may only experience a few fractures throughout their lives, often in childhood, and may have normal or near-normal height and lifespan. In contrast, severe forms can lead to multiple fractures before birth or in early infancy, significant skeletal deformities, and can be life-threatening due to respiratory complications or intracranial haemorrhage [PMID:33604313].

Specific lifetime risks include recurrent fractures, with the frequency decreasing after puberty for many. Progressive hearing loss affects a significant proportion of adults with OI. There is also an increased risk of scoliosis and kyphosis, which can lead to pain and, in severe cases, impact lung function. Dental issues like dentinogenesis imperfecta affect around half of individuals with OI. The age of onset for fractures can range from prenatally in severe types, through childhood and adulthood in milder forms. While lifespan is generally normal for milder types, it can be reduced in severe forms, especially Type II.

Genetic causes

Osteogenesis Imperfecta is typically caused by genetic changes in genes responsible for producing type I collagen, the most abundant protein in bone, skin, and other connective tissues. The primary genes involved include *COL1A1* and *COL1A2*. These genes provide instructions for making the two main protein chains (alpha-1 and alpha-2) that assemble to form type I collagen. Pathogenic variants in *COL1A1* or *COL1A2* can lead to either a reduced amount of normal collagen or the production of structurally abnormal collagen, both of which weaken bone [PMID:27091845].

In some cases, OI is caused by variants in other genes, such as *CRTAP*. The protein made from the *CRTAP* gene plays a crucial role in modifying collagen after it is made, specifically in a process called prolyl 3-hydroxylation. Pathogenic variants in *CRTAP* can disrupt this important modification step, leading to the production of abnormal collagen that compromises bone quality and strength [PMID:21727780].

The normal function of these genes is to ensure the production of strong, well-structured type I collagen. When genetic variants disrupt this process, the resulting collagen is either deficient in quantity or of poor quality. This leads to bones that lack their usual strength and resilience, making them brittle and prone to fracture, which is the hallmark of Osteogenesis Imperfecta.

• COL1A1
  collagen type I alpha 1 chain
  The COL1A1 gene provides instructions for producing a key component of type I collagen, a protein vital for strengthening various connective tissues throughout the body.
• COL1A2
  collagen type I alpha 2 chain
  The COL1A2 gene provides instructions for producing a component of type I collagen, a crucial structural protein found in bones, skin, and other connective tissues throughout the body.
• CRTAP
  cartilage associated protein
  The *CRTAP* gene provides instructions for making a protein crucial for bone formation and mineralisation, and variants in this gene are linked to certain forms of osteogenesis imperfecta.

Inheritance pattern

Osteogenesis Imperfecta typically follows an autosomal dominant (AD) inheritance pattern, meaning a person only needs to inherit one copy of the altered gene from one parent to develop the condition. In most autosomal dominant cases, the condition results from a new (de novo) genetic change that occurred in the affected individual and was not inherited from either parent. However, it can also be inherited from an affected parent, with each child having a 50% chance of inheriting the variant.

Less commonly, OI can be inherited in an autosomal recessive (AR) pattern. This means an individual must inherit two copies of the altered gene, one from each parent, to develop the condition. Parents who carry one copy of the altered gene are typically unaffected and are called carriers. If both parents are carriers, there is a 25% chance with each pregnancy that their child will inherit two altered gene copies and develop OI, a 50% chance the child will be an unaffected carrier, and a 25% chance the child will inherit two normal gene copies.

Genetic counselling can provide detailed information about the specific inheritance pattern for a family and the associated risks for relatives.

Subtypes & variants

This page covers Osteogenesis imperfecta (all types) as a single condition. Several distinct variants and clinical subtypes are recognised in the literature - they share the underlying biology and broad management approach, but differ in severity, age of onset, or causative gene:

• Type I (mild) OMIM 166200

  Most common form. Blue sclerae, mild bone fragility, normal stature. Fractures decrease after puberty. Typically autosomal dominant COL1A1 variants reducing collagen quantity (haploinsufficiency).

• Type II (lethal perinatal) OMIM 166210

  Severe form, usually lethal in the perinatal period from respiratory insufficiency due to severe rib fractures and underdeveloped lungs. Caused by structural COL1A1 / COL1A2 variants.

• Type III (severe progressive) OMIM 259420

  Severe progressively deforming form. Multiple fractures from infancy, short stature, bone deformity, scoliosis. White sclerae in adulthood. Mobility often requires wheelchair.

Diagnosis & testing

Diagnosing Osteogenesis Imperfecta typically involves a combination of clinical assessment, imaging studies, and genetic testing. A clinical diagnosis is often suspected based on recurrent fractures, bone deformities, blue sclera, and other characteristic features. X-rays and other imaging techniques can reveal evidence of past fractures, bone density issues, and characteristic bone changes.

Genetic testing is crucial for confirming the diagnosis and identifying the specific genetic cause, which can help predict disease severity and guide management. For individuals with suspected OI, referral to a clinical genetics service through the NHS Genomic Medicine Service (GMS) is appropriate. Genetic testing for OI falls under various NHS National Genomic Test Directory R-codes, such as R253 Osteogenesis imperfecta and R430 Paediatric rare disease, depending on the specific clinical presentation and age of onset. These tests analyse genes like *COL1A1*, *COL1A2*, and *CRTAP* to identify pathogenic variants. A genetic counsellor can explain the testing process and implications in detail.

Management & lifestyle

Managing Osteogenesis Imperfecta focuses on minimising fractures, managing pain, promoting mobility, and optimising bone health and overall quality of life. This involves a multidisciplinary team approach, often including orthopaedic surgeons, physiotherapists, occupational therapists, pain specialists, and geneticists. Medical treatments, such as bisphosphonate therapy, are commonly used to help strengthen bones and reduce fracture rates, particularly in children [PMID:33604313].

Surgical interventions, including rod insertion into long bones (intramedullary rodding) to prevent fractures and correct deformities, are often necessary. Physiotherapy and occupational therapy are vital for improving muscle strength, mobility, and functional independence, as well as providing guidance on safe movement and adaptive equipment. Pain management strategies are also crucial, as chronic pain can be a significant issue for individuals with OI.

Regular monitoring for potential complications such as hearing loss and scoliosis is important. Genetic counsellors can provide essential support and information regarding the genetic aspects of OI, inheritance patterns, and family planning. Individuals with OI are typically managed within the NHS framework, accessing specialised services and ongoing support as part of their long-term care plan.

UK care pathway

In the UK, individuals with suspected or diagnosed Osteogenesis Imperfecta are generally referred to specialist services within the NHS. The NHS Genomic Medicine Service (GMS) provides the framework for accessing genetic testing, which is crucial for confirming the diagnosis and guiding care. Clinical geneticists and genetic counsellors play a key role in explaining the condition, its inheritance, and the implications for the individual and their family.

For genetic testing, appropriate R-codes from the NHS National Genomic Test Directory, such as R253 (Osteogenesis imperfecta) or R430 (Paediatric rare disease), would be used. Once diagnosed, ongoing care is typically managed by a multidisciplinary team. This team may include orthopaedic specialists, endocrinologists, audiologists, and physiotherapists, all working together to provide comprehensive support and management tailored to the individual's specific needs.

Related conditions

While Osteogenesis Imperfecta is distinctive in its presentation, some other conditions might present with overlapping features, particularly bone fragility. Conditions like idiopathic juvenile osteoporosis or certain forms of rickets might initially be considered in a differential diagnosis, although their underlying causes and typical presentations differ from OI.

Some rare forms of bone dysplasia or metabolic bone disorders can also present with skeletal fragility. However, the specific constellation of symptoms, including blue sclera, dentinogenesis imperfecta, and hearing loss, alongside the genetic findings in genes such as *COL1A1*, *COL1A2*, or *CRTAP*, typically help to differentiate OI from other conditions.

• Ehlers-Danlos syndrome (arthrochalasia)
  Connective Tissue
  Shares 2 genes
• Otosclerosis
  Hearing Loss
  Shares 1 gene

Frequently asked questions

References

1. Liu L, Sun L, Chen Y. Delineation of dual molecular diagnosis in patients with skeletal deformity. Orphanet journal of rare diseases. 2022. PMID: 35346302
2. Iwamoto J, Takeda T, Sato Y. Efficacy of oral etidronate for skeletal diseases in Japan. Yonsei medical journal. 2005. PMID: 15988801
3. Moumoulidis I, Axon P, Baguley D. A review on the genetics of otosclerosis. Clinical otolaryngology : official journal of ENT-UK ; official journal of Netherlands Society for Oto-Rhino-Laryngology & Cervico-Facial Surgery. 2007. PMID: 17651264
4. Al Kaissi A, Ryabykh S, Ben Chehida F. The Tomographic Study and the Phenotype of Wormian Bones. Diagnostics (Basel, Switzerland). 2023. PMID: 36900016
5. Busschers E, Chen-Everson Y, Adeyeye M. Anti-transforming growth factor-β treatment shows increased bone mass and strength in a novel mouse model for osteogenesis imperfecta type I. Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research. 2025. PMID: 40358008
6. Bradbury LA, Barlow S, Geoghegan F. Risedronate in adults with osteogenesis imperfecta type I: increased bone mineral density and decreased bone turnover, but high fracture rate persists. Osteoporosis international : a journal established as result of cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA. 2012. PMID: 21739105
7. Lund AM, Müller J, Skovby F. Anthropometry of patients with osteogenesis imperfecta. Archives of disease in childhood. 1999. PMID: 10332000
8. Veilleux LN, Lemay M, Pouliot-Laforte A. Muscle anatomy and dynamic muscle function in osteogenesis imperfecta type I. The Journal of clinical endocrinology and metabolism. 2014. PMID: 24248189