Osteogenesis imperfecta

Synonyms in the broadest sense

Brittle bone disease, congenital bone fragility, fragilitas osseum

Definition

Osteogenesis imperfecta (brittle bone disease) is a congenital disorder of the collagen balance. Collagen is a structure of the connective tissue. This makes the bones abnormally brittle.

The gene mutation affects not only bones, but also tendons, ligaments, teeth and the conjunctiva of the eye, because collagen is also found everywhere. Brittle bone disease is a congenital disorder of the collagen balance. The disease is inherited and is accompanied by abnormal bone fragility.

It mainly affects a substance inside the bones, causing the bone to lose a lot of stability. In addition to bone fractures (frequent fractures, med. fracture), the characteristics are also malformations of the bones and also short stature.

Mentally, however, the patients are inconspicuous. The frequency of bone fractures decreases after puberty, but can increase again with age. The diagnosis of brittle bone disease is usually made on the basis of X-rays, on which the greatly reduced bone density is clearly visible.

The therapy consists of increasing the bone density by the administration of bisphosphonates. The bones are also splinted internally and externally. From the outside, for example, the legs are embedded in a splint. An intramedullary nail, which is inserted into the bone and can grow with it, splints the bone from the inside.

Cause

Various gene mutations are suspected to be the cause of osteogenesis imperfecta. There are over 200 type I collagen gene mutations. These are located on chromosome 7 or 17, and if this gene is defective, the production of collagen is insufficient.

In type I brittle bone disease (see below), normal colleagues are produced, but too little of it. In all other types, the collagen produced is defective and cannot perform its function in the body sufficiently. Some of the gene mutations also occur spontaneously and thus newly.

Osteogenesis imperfecta can be inherited both autosomal recessively and autosomal dominant. This means that the probability of inheriting osteogenesis imperfecta to the next generation depends essentially on the individual type. If osteogenesis imperfecta is present, the bone cannot reproduce properly, i.e. it cannot form new bone and thus cannot stabilize.

Bones contain a structure that can be imagined as fine beams (similar to a sponge) that are cross-linked with each other. They give the bone an extraordinary stability. It is precisely these structures that can be narrow and sparse in osteogenesis imperfecta.

There are different forms of the glass bone disease (Osteogenesis imperfecta). In the case of mild forms, the glass bone disease only becomes apparent over the years – for example, because a child repeatedly suffers bone fractures. The most severe forms of vitreous bone/osteogenesis imperfecta can make a newborn child unfit for life.

The newborn is already born with several fractures; even stillbirths can occur sporadically. Overall, vitreous bone disease is a rather heterogeneous clinical picture (which means that many different symptoms can come together). Thus, there can be many different symptoms of vitreous bone disease, without it being possible to say that there is a specific characteristic that occurs in all patients.

Typical are:The fractures (broken bones) can occur with even the slightest movement, such as turning around in bed. This again depends on the severity of the characteristic. It is quite possible that children are not even able to learn to stand or even walk because of this increased bone fragility.

Typically, the tubular bones (arm and leg bones) and the pelvic bones are affected by the disease. The reduced stability of the bones can also cause them to bend due to the high muscle tension. Internal organs can also be affected, as they also consist of collagen.

These organs then lose more and more of their functionality over time. Patients with vitreous bones show a conspicuous bluish shimmering of the eyes: Due to the collagen deficiency (also in the conjunctiva of the eye), the choroid underneath shimmers bluish through. However, it is important that the patients do not show any mental weaknesses (medically also called retardation).

  • Fractures, also of the skull
  • Malformations
  • Childhood
  • Hearing loss
  • Easy vulnerability
  • Overstretchability of the joints and
  • Bad teeth.
  • Type IThis is the mildest form of Osteogensis imperfecta and is often not detected immediately, but only when the children are a little older and often break something (for example, when learning to walk). The physique is usually normal and the bone deformations are minor. Patients often become hard of hearing after puberty.

    Type I Osteogenesis imperfecta is the most common type of hearing loss in the population.

  • Type IIDies is the most severe form of osteogenesis with hardly or not at all viable patients, who often died during or shortly after birth. In the meantime, however, cases have been described in which children with type II are viable.
  • Type IIID Patients with type III of the disease have a greatly increased bone fragility and growth retardation. Arms, legs and spine are severely deformed. Patients often soon need a wheelchair.
  • Type IV patients are often also small in stature, but less severely affected than Type III patients, although there may be very different degrees of severity, bone fragility and bone deformities.