Osteogenesis Imperfecta (Brittle Bone Disease)

What happens in osteogenesis imperfecta

Bone is built on a scaffold of type 1 collagen, onto which minerals are laid. In most OI, a change in the COL1A1 or COL1A2 gene leads to either:

• too little normal collagen (milder forms, such as type I), or
• abnormally structured collagen (more severe forms, types II to IV)

The result is weak, brittle bone. Collagen is also important in the eyes, teeth, ligaments, skin and ears, which explains the other features.

Inheritance

Most OI is autosomal dominant: a parent with OI has a 50% chance of passing it to each child. Many cases arise from a new gene change with no family history. Rarer types are recessive, involving genes such as CRTAP, P3H1 and others.

Types of osteogenesis imperfecta

The traditional Sillence classification is still widely used:

Symptoms

• fractures from minor trauma, especially in childhood; frequency usually decreases after puberty
• blue, purple or gray sclerae (whites of the eyes)
• short stature, from mild to severe
• bone deformity: bowing of the long bones, chest deformity
• scoliosis and kyphosis
• brittle, discolored teeth (dentinogenesis imperfecta)
• hearing loss (conductive hearing loss and nerve-related loss): often starting in the late teens to 40s, from changes in the middle and inner ear
• loose joints and low muscle tone
• easy bruising
• breathing problems in severe forms
• bone pain and fatigue

Diagnosis

• Clinical features and family history
• X-rays: thin bones, healing fractures, deformities and wormian bones (small extra bones in the skull)
• Bone density scan (DXA): OI is one cause of low bone density in children and young adults, alongside other causes of osteoporosis
• Genetic testing: confirms the diagnosis in most people and guides family counseling
• Prenatal ultrasound can detect severe forms; genetic testing can be offered in families with a known variant
• Hearing tests and dental assessment

OI and suspected child abuse

Unexplained fractures in an infant raise concern about child abuse. Mild OI can be mistaken for abuse and vice versa. Doctors consider family history, eye and tooth features, X-ray findings and genetic testing to distinguish them, with careful, multidisciplinary assessment.

Treatment

The goals are fewer fractures, better mobility and independence, and managing pain.

• Fracture care: casting or splinting, with early movement to avoid bone loss from immobility
• Bisphosphonates: IV pamidronate or zoledronic acid, or oral forms, increase bone density and reduce fractures and pain, especially in children with moderate to severe OI
• Surgery: telescoping rods inserted in long bones to straighten them and prevent fractures; spinal surgery for severe scoliosis
• Physical and occupational therapy: safe strengthening, swimming and mobility aids
• Hearing care: hearing aids or surgery (stapedectomy) for some types of hearing loss
• Dental care: protecting teeth with crowns and regular dental follow-up
• Nutrition: adequate calcium, vitamin D and protein
• Newer therapies under study include drugs that build bone or block sclerostin

Living with OI

• plan safe physical activity, especially swimming and supervised exercise
• use protective handling techniques for babies and young children
• check bone health regularly
• get regular hearing tests from adolescence
• seek genetic counseling for family planning
• connect with support organizations for practical advice

Outlook

Life expectancy is normal or near normal for people with type I and many with type IV. Type III can shorten life, mainly from breathing complications. Type II is usually fatal around birth. With modern treatment, many people with OI attend school, work and live independently.

Frequently asked questions

What is osteogenesis imperfecta?

Osteogenesis imperfecta is an inherited condition that makes bones fragile and prone to breaking, often from minor injuries. It is caused by changes in genes that produce collagen, the protein framework of bone. Severity ranges from mild to life-threatening.

What causes osteogenesis imperfecta?

Most cases are caused by changes in the COL1A1 or COL1A2 genes, which make type 1 collagen. It is usually inherited in an autosomal dominant pattern, though many cases result from a new gene change. Rarer recessive types involve other genes.

What are the signs of osteogenesis imperfecta?

The main sign is fractures from minor trauma. Others include blue or gray whites of the eyes, short stature, bowed bones, scoliosis, brittle or discolored teeth, loose joints and hearing loss that often begins in early adulthood.

Is there a cure for osteogenesis imperfecta?

There is no cure. Treatment with bisphosphonates, surgical rods, physical therapy, and hearing and dental care reduces fractures and improves function. Research into new drugs and genetic therapies is ongoing.

What is the life expectancy with osteogenesis imperfecta?

People with milder types (I and many with IV) usually have a normal or near-normal life expectancy. Severe type III can shorten life, mainly due to breathing problems. Type II is usually fatal before or shortly after birth.