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OSTEOGENESIS IMPERFECTA (OI)

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OSTEOGENESIS IMPERFECTA (OI)

Osteogenesis imperfecta is a group of genetic disorders marked by extremely fragile bones that break or fracture easily, often from little or no apparent trauma or cause.

  • The condition is also called brittle bone disease.
  • The severity of OI varies from person to person, even among individuals of the same family
  • It ranges from mild to severe. A person may have just a few or as many as several hundred fractures in their lifetime.
  • Most cases are mild resulting in few bone fractures, the severe form can cause hearing loss, spinal cord problems, heart failure as well as permanent deformities.
  • The condition can be life-threatening if it occurs in babies either before or after birth.
  • .The condition affects both male and female equally and affects about 1 in 15,000 people.

CAUSES

Osteogenesis imperfecta is a genetic disorder that is caused by a mutation in the COL1A1 or COLIA2 gene inherited in an autosomal dominant pattern or occur via a new mutation.

This means that a child inherits the defective gene from one of their parents or neither parent has it but the defect occurs due to a spontaneous mutation (change) in the gene, and it stops working properly.

This gene produces a protein (type 1 collagen), a major component of the connective tissues in bones. Type 1 collagen is also important in forming teeth, ligaments and the sclera (the white outer tissue of the eyeballs)

TYPES

  • There are eight types with type 1 being the least severe and type 8 being the most severe.
  • The first four types are the most common while the last four are extremely rare, and most are subtypes of type 4 OI.
Type 1 OI

is the mildest and the most common of the condition. In this type, the body produces the normal quality of collagen but in insufficient quantities. These results in mildly fragile bones and bone fracture may occur due to mild trauma. Bone fracture usually occurs during childhood through puberty and may be less common after puberty.

Features may include

  • Bluish discoloration of the sclera (blue sclera)
  • Abnormalities in the middle or inner ears resulting in hearing impairment
  • Loose joints
  • Low muscle tone
  • Bone fractures easily
  • An abnormal outward curvature of the upper spine (kyphosis)
  • An abnormal lateral curvature of the spine (scoliosis)
  • Slight protrusion of the eye
  • According to researchers, a subgroup of type 1 exist is characterized by opalescent teeth in addition to the above mentioned features.
Type II OI

This type is the most severe type and can cause life-threatening complications at, or shortly after birth. In this type, the body produces insufficient collagen or produces collagen that is of poor quality. Most children born with the type die within the first year of life due to respiratory failure due to underdeveloped lungs. This type is subclassified into groups A, B, C which are distinguished by bone formation seen only on x-ray.

Features

  • Underdeveloped lungs
  • Severe bone deformity and small stature
  • Narrowed chest
  • Type IIA have broad and short long bones with broad and beaded ribs
  • Type IIB demonstrates broad and short long bones with thin ribs with little or no beading
  • Type IIC shows thin and longer long bones with thin and beaded ribs
TYPE III OI

In type III, enough collagen is made but it is defective and causes the bone to break easily. Bone deformities are common and present at birth. They may become worse as affected children ages.

Features

  • Severe bone deformities
  • Loose joints
  • Triangular face
  • Poor muscle tone in arms and legs
  • Early loss of hearing is possible
  • Discoloration of the sclera
  • Short Stature
  • Respiratory problem is possible
  • Brittle, discolored teeth may also be present
TYPE IV OI

This type is the most variable because symptoms range from mild to severe. In this type, enough collagen is made but it is not of high quality.

Features

  • Bones fracture easily, especially before puberty
  • Short Stature
  • Mild to moderate bone malformation
  • Hearing impairment
  • Spinal curvature
  • Bowed legs that may lessen with age

DIAGNOSIS

The condition is diagnosed by taking x-rays. This allows the doctor to see current and broken bones as well as view defects in the bones.

A laboratory test may be done. This may include taking blood or tissue samples for genetic testing

TREATMENT

No cure exists for this condition but there are supportive therapies that help reduce the risk of broken bones and may increase the quality of life.

Physiotherapy used to strengthen muscles

Physical aids such as crutches, wheelchairs, grabbing arms

Medicine to reduce any pain

Bisphosphonate medications to strengthen child’s bone

Low-impact exercise for bone building

Surgery which may include inserting a metal rod in the long bones to improve strength