What is Osteogenesis Imperfecta (brittle bone disease)?

Osteogenesis imperfecta (OI), also known as brittle bone disease, is a genetic disorder that primarily affects bone strength, making them susceptible to fracture easily, even with minor injuries or no apparent cause [1]. This disease results from a defect or mutation in the genes responsible for producing type I collagen, a fundamental protein that gives bones their strength and flexibility [1]. This defect leads the body to produce insufficient amounts of collagen or to produce defective collagen, which weakens the bone structure and makes it brittle [1].

The impact of the disease is not limited to bones, as type I collagen is present in other connective tissues such as tendons, ligaments, skin, and lungs, meaning these tissues may also be affected [1]. The severity of the disease ranges from very mild cases where a person experiences a few fractures throughout their life, to very severe cases that may lead to multiple fractures before or shortly after birth, accompanied by serious medical complications [1].

The Different Types of Osteogenesis Imperfecta

There are several types of osteogenesis imperfecta, and these types vary in their severity, symptoms, and the nature of the underlying genetic defect. Among the most prominent of these types are:

• Type I: This is considered the mildest and most common type. It is characterized by bone fractures that often occur before puberty, and stature may not be significantly affected. Symptoms such as loose joints, muscle weakness, blue, gray, or purple-tinted whites of the eyes (sclera), and hearing loss may occur [1].
• Type II: This is the most severe form and often leads to death at or shortly after birth due to multiple prenatal fractures and breathing problems resulting from incomplete lung development [1].
• Type III: Considered one of the most severe types among those who survive the neonatal period. It is characterized by very frequent fractures with minimal trauma, severe bone deformities, short stature, and patients may suffer from lung problems that worsen with age [1].
• Type IV: Its symptoms are similar to Type I, but it is often more severe. Fractures may occur easily, stature is shorter than average, and mild to moderate bone deformities may appear [1].

There are also other rare types (such as types V through VIII) that differ in their clinical and genetic characteristics and may share some symptoms with the more common types [1].

Symptoms and Signs of Osteogenesis Imperfecta

In addition to osteoporosis and frequent fractures, people with osteogenesis imperfecta may experience a wide range of other symptoms that vary in severity from person to person. These symptoms include [1], [2]:

• Short stature.
• Whites of the eyes that appear blue, purple, or gray.
• Easy bruising.
• Loose joints and muscle weakness.
• Deformities or bowing of long bones.
• Curvature of the spine (scoliosis or kyphosis) or vertebral compression.
• Brittle, discolored, or malformed teeth, which may not be properly aligned.
• Hearing loss, which can begin at an early age.
• Breathing problems, especially in the more severe types.
• Hip joint deformity (coxa vara).

Causes of the Disease and Inheritance

Osteogenesis imperfecta is caused by a mutation in one or more genes that carry the instructions for producing type I collagen [1]. In most cases, this abnormal gene is inherited from one of the parents, or the genetic mutation may occur spontaneously for the first time in the affected person [1]. There are dominant and recessive forms of inheritance for the disease:

• Dominant Inheritance: In this form, having a single abnormal copy of the disease-causing gene is sufficient for symptoms to appear. A person with dominant inheritance has a 50% chance of passing the disease to each of their children [1].
• Recessive Inheritance: In this form, the child must inherit an abnormal copy of the gene from both parents to be affected by the disease. Parents in this case may not be affected by the disease but are carriers of the gene [1].

Genetic counselors can provide detailed information about inheritance patterns and potential risks for families [1].

Next Steps

If you suspect that you or your child has symptoms of osteogenesis imperfecta, it is essential to consult a doctor to undergo the necessary examinations [2]. Diagnosis may include a physical examination, medical and family history, X-rays, and collagen or genetic testing [3]. There is currently no cure for the disease, but treatments are available that aim to reduce pain and complications and improve quality of life [2]. For more information on how to live with this disease, you can visit Living with Osteogenesis Imperfecta (Brittle Bone Disease): Comprehensive Care and Psychological Support (Arabic).

Medical references

• Osteogenesis Imperfecta
• Osteogenesis imperfecta
• Osteogenesis Imperfecta