What is osteogenesis imperfecta?

Osteogenesis imperfecta is part of the family of rare bone diseases. It is a genetic disease characterized by reduced bone mass and bone fragility. The cause: an anomaly in the production of collagen, a protein involved in the constitution and maintenance of bone.

Different types of osteogenesis imperfecta

This genetic disease affects one in 15,000 people. In Europe, there are around 5,000 sick people. The disease can affect men and women, children and adults alike. There are several types of illnesses, depending on their degree of severity.

Developed at the end of the 1970s, the Sillence classification describes 7 types (4 initially) depending on the severity of the symptoms and its impact on daily life. “For mild forms, we speak of brittle bone disease. Types 3 or 4 are more serious”, describes Professor Roland Chapurlat, rheumatologist and specialist in bone pathologies at the Hospices Civils de Lyon.

Although it makes it possible to classify the different variations of the disease, the Sillence classification does not make it possible to describe all the clinical specificities. While the most severe forms appear during intrauterine life, the benign forms are more marked in adulthood.

Bone fragility and repeated fractures

Of genetic origin, the disease is hereditary (the risk of transmission at birth is around 50%), but it is not contagious. It results in bone fragility and low bone mass, leading to repeated fractures. “The first signs appear in the first months. In the arms of his parents, the child may fracture an arm or a vertebra. We can also observe the first fractures when learning to walk.continues the specialist.

In addition to bone fragilities and deformations, osteogenesis imperfecta is also characterized by cranial or spinal deformations, notably through very marked scoliosis or deformations of the chest wall, for example.

Other symptoms may also be present depending on the type of osteogenesis imperfecta.

• Thus, growth difficulties, vascular fragility or cardiovascular anomalies (aneurysms, heart valve anomalies) may be evident.
• Weakness of dentin, premature wear of teeth and unusual formation of caries may also be observed. “Another specific sign, especially visible in type I, is the blue-gray appearance of the sclera of the eye. about Pr Roland Chapurlat.
• Damage to the hearing system (hearing loss up to deafness) is also possible, particularly in types I and III.
• Fragility of the skin, ligamentous hyperlaxity and short stature are also symptoms noted in severe forms of the disease.
• Finally, pain (particularly linked to osteoarthritis) and fatigue remain two characteristic symptoms found in all the forms that this bone disease can take.

Diagnosis of osteogenesis imperfecta

Diagnosis of osteogenesis imperfecta can be difficult because it can be confused with other bone diseases. During pregnancy, a well-conducted ultrasound can reveal limb abnormalities as well as intrauterine growth retardation, in the most serious forms. “Typically, the disease is not diagnosed before birth unless there is already a case in the family.” specifies the rheumatologist.

If the disease is suspected, given a characterized clinical picture, a genotype is then considered. “It’s a simple test to perform. From a blood test, we can obtain the name and location of the genetic mutation,” continues Professor Roland Chapurlat. In certain cases, additional examinations, such as bone densitometry and a skull x-ray, may be considered.

Management of osteogenesis imperfecta

To date, there is no curative treatment. “However, clinical trials currently underway suggest prospects for effective drugs within a few years.” assures Professor Roland Chapurlat.

Currently, bisphosphonates, a class of drugs used in bone diseases, are usually prescribed in children to reduce pain and fractures. Prescribed intravenously, these treatments often cause side effects. In the most severe forms, preventive nailing can be scheduled to reduce the risk of fractures. “This involves placing a titanium nail in the center of the bone to strengthen it.explains Professor Roland Chapurlat.

In order to alleviate dental problems, taking fluoride, vitamin D and calcium is often recommended, as is the installation of crowns on baby teeth. “In all cases, regular medical follow-up with a specialized dentist is essential. points out the rheumatologist. A cardiovascular and phosphocalcic assessment must also be carried out.

In periods of acute pain, rehabilitative treatment and the prescription of respiratory physiotherapy sessions can also be provided.

Finally, in the case of significant spinal deformities, surgical intervention can sometimes be the only possible recourse.

Life expectancy

Depending on the severity of the disease, life expectancy may be impacted. In mild forms, type I, life expectancy is almost identical compared to the rest of the population. On the other hand, for more severe forms, it can be reduced by around ten years, due to possible pulmonary or cardiovascular complications. “Scoliosis hampers respiratory capacity and promotes the occurrence of a lung infection.explains Professor Roland Chapurlat.

Faced with characteristic clinical signs, it is therefore important not to neglect the possibility of this disease.