Osteogenesis Imperfecta

Osteogenesis imperfecta or OI, also known as brittle bone disease, is a genetic disorder that is characterized by weak and fragile bones that break easily. Osteogenesis imperfecta is caused by a genetic defect that disables the body to make strong bones. A person may experience occasional fractures or may have multiple fractures throughout life depending upon the severity of Osteogenesis imperfecta present. Apart from fragile bones, people with OI suffer from teeth problems - Dentinogenesis Imperfecta, hearing loss, muscle weakness, loose joints (joint laxity) and skeletal malformations.

Causes of OI

Osteogenesis imperfecta is either inherited from a parent who has the defective gene or could be a result of new mutations. Due to the defective gene, an important protein substance called type I collagen is not produced in the body. This protein plays an important role in forming connective tissues in bones and also helps in forming ligaments, teeth and the white outer tissue of the eyeballs (sclera). Due to poor production of the protein, bones become brittle and fragile and tend to break easily. Most of the mutations in OI exist in the two type I collagen genes, COL1A1 and COL1A2 and account for almost all the forms of OI.

Classification of Osteogenesis imperfecta

Depending upon the severity of the Osteogenesis imperfecta, the condition is divided into type 1, type 2, type 3, type 4. These types are classified mostly by fracture frequency and by characteristic features. Recently, research has identified three more additional variations to Osteogenesis imperfecta known as type 5, 6 and 7.

Type 1

Type 1 Osteogenesis imperfecta is the mildest and the most common form of OI. More than 50% patients suffer from Type 1 Osteogenesis imperfecta. In this type, though body produces normal type I collagen but only half the normal quantity. People with Type 1 OI may experience fewer fractures, and most often the condition may go unnoticed for several years after their birth.

Type 2

Type 2 Is the most severe form of Osteogenesis imperfecta often resulting in bone deformities in the child. Type 2 OI normally turns out to be fatal with the production of very little or poor quality collagen being produced in the body. Infants with type 2 OI are born with fragile rib cage and underdeveloped lungs. They usually die either in the womb or soon after birth.

Type 3

Osteogenesis imperfecta type III is severely progressive type associated with symptoms like short stature, a triangular face, severe scoliosis, grayish sclera, and Dentinogenesis imperfecta (impaired and irregular teeth with yellow-blue tinge). Infants with type 3 OI have fractures at the time of birth itself, and few infants reveal a fractured and eventually healed bones in the womb itself.

Type 4

Type 4 Osteogenesis imperfecta can range from very mild to severe form often resulting in growth retardation in children. A child with type 4 OI is short with bow shaped legs. Symptoms like tinted sclerae (white of the eye) and dental deformities may also be present at the time of the birth. Child normally suffers from Long bone fractures, vertebral compression, scoliosis, and ligament laxity with type 4 OI.

Type 4 also has two sub types called type 5 and type 6 OI. Though clinically they resemble type 4, types 5 and 6 have unique patterns to the bones. Type 5 exhibits features like ossification of interosseous membrane of the forearm with radial head dislocation, large callus formation and an abnormal histopathological pattern. Type 6 will have elevated alkaline phosphatase and blue-white sclerae.

Diagnosis

Most severe forms are diagnosed before birth itself. Ultrasound scanning during second trimester may reveal deformity of limbs, abnormally short fetus, irregular skull shape, lack of mineralizations and narrow chest cavity. Few cases are diagnosed soon after the birth and mild type of OI is found out much later in life when such individuals suffer from repeated fractures. However, the following diagnostic methods are used to assess the condition.

• Clinical examination, wherein history of frequent fractures with minimal trauma is noted
  
  
• X-Ray
  
  
• Genetic testing of a blood sample (DNA )
  
  
• Skin biopsy to assess collagen production.

Treatment

Since Osteogenesis imperfecta is a genetic condition, it does not have a cure. Patient will be treated symptomatically and will be aided with external tools to provide maximum possible mobility. Efforts are also taken to improve muscle strength and boost the bone mass in the patient through physical therapy. Professionally designed exercise programmes are highly beneficial and play an important role in treating the patients suffering from OI. Patient may also be prescribed required nutritional supplements like calcium, and vitamin D along with physical therapy. Few suitable candidates are also treated with surgical procedure called intramedullary rod surgery wherein metal rods are inserted through the length of the long bones to support and strengthen them.

Of late, Bisphosphonates drugs are being used in treating Osteogenesis imperfecta. Bisphosphonates are used to decrease the amount of bone resorption. It also helps in preventing fractures and improve person's functional mobility. There is also research being done to understand the role of gene therapy in treating Osteogenesis imperfecta.

Prognosis

Prognosis of Osteogenesis imperfecta depends upon the severity of the conditions. Despite bone deformity, restricted activity, and short stature, often patients with OI lead productive and near to normal lives.

Terminologies :

• Osteogenesis : Growing new bone
  
• Osteocytes : Bone cells
  
• Osteoblasts : Bone cells building new bone structure
  
• Osteoclasts : Bone cells which scavange bone tissue