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*** Classification of OI types ***

Clinical Classification of OI types
based on the original classification by Sillence et al. (1)

• Type IA
  • most frequent type,
    
  • fragile bones,
  • widely varying fragility,
  • blue sclerae,
  • rarely fractures at birth; onset of fractures often after 1st year of life,
  • hearing loss with about 50% of patients, usually starting after puberty,
  • height usually below average,
  • deformities usually moderate,
  • so called "Wormian Bones" at Birth (Mozaic cranium on X-ray),
  • often loose joints,
  • heredity, see inheritance.
  
  
• Type IB
  Same as Type IA, but with dental problems (dentinogenesis imperfecta)
  
  
• Type II
  This is also called the lethal form of OI.
  • children are often stillborn or die shortly after birth,
  • many fractures, often already at or before birth,
  • almost no ossification of the skull; soft cranium,
  • deformities of the legs, arms and ribs,
  • heredity, see inheritance.
  
  
• Type III
  • severe fragility of the skeleton,
  • severe growth retardation,
  • deformities of the arms, legs and spine,
  • often a relatively large head with a characteristic shape
    (triangular with broad forehead and pointed chin),
  • blue sclerae, later turning white,
  • sometimes hearing loss,
  • sometimes dentinogenesis imperfecta,
  • often leading to physical disability,
  • heredity, see inheritance.
  
  
• Type IVA
  • strongly variable in severity,
  • fragility light to severe,
  • deformities moderate to severe,
  • moderate to serious growth retardation,
  • white sclerae, or blue at first, turning white later,
  • sometimes hearing loss,
  • heredity, see inheritance.
  
  
• Type IVB
  Same as type IVA, but with dentinogenesis Imperfecta.

Note:
In these original definitions there is no mention of mild or severe types. Some "OI experts" have developed a tendency to speak about e.g. OI type I as a mild type. We are of the opinion that this is not only an error, but that it does injustice to OI people.
Mild or severe types of OI do not exist. A person can be more or less severely affected by the condition, but this is not connected to the type of OI.

It has been established that in type(s) I the defect causes a reduced production of normal collagen, sometimes resulting in a low bone mineral density (BMD); while in the other types structurally abnormal collagen (sometimes also in a lower amount) is produced, resulting in low quality bone usually with a low BMD. Until now, any further clear correspondence between the clinical types as defined above and the genetical defects causing OI has not been found.

The importance of typing should not be overestimated. It may be helpful to your doctor in making a treatment plan, or for you in testing your doctor's OI knowledge. May be it is more interesting what type of person you are than what type of OI you have. In daily life the severity of the condition could be the most important. The severity is not coupled to the type of OI.

(1)
D.O. Sillence, A. Senn, D.M. Danks
Genetic heterogeneity in osteogenesis imperfecta
J. Med. Genet. 16 (1979) 101-116

There have been several proposals to extend the original Sillence typing, but these "new" types (V and VI)are not based on clinical observations but on histological facts, making it somewhat more difficult to establish them. They are special cases of type IV and have not gained universal acceptance yet.

In the old days OI was classified as OI congenita or OI tarda, meaning that the OI manifested itself before birth or sometime thereafter. These terms have become obsolete.

WARNING:
Classification should not be used for "self diagnosis", seek the advice of a medical specialist familiar with OI.

last updated 3 August 2005