Different forms of osteogenesis imperfecta

Osteogenesis imperfecta may be classified according
to severity into four basic phenotypes
(Sillence classification). Although the classification
does not correspond to the types of mutation,
it has in general proved clinically useful. Ol
types I and IV are less severe than type II (lethal
in infancy) and type III. Three radiographs show
a relatively mild (but for the patient nevertheless
very disabling) deformity of the tibia and
fibula in Ol type IV (1); severe deformities in the
tibia and fibula in Ol type III (2); and the distinctly
thickened and shortened long bones in
the lethal Ol type II (3). Mutations in Ol are
autosomal dominant, the severe forms being
due to de novo mutations. Germline mosaicism
has been shown to account for rare instances of
affected siblings being born to unaffected
parents.