Brittle bone syndrome is caused by:

 # Brittle bone syndrome is caused by:

A. Improper synthesis of procollagen 

B. Polymerisation of collagen 

C. Increase osteoclastic activity 

D Increase fibroblastic activity 

The correct answer is A. Improper synthesis of procollagen.

Osteogenesis imperfecta, also known as Brittle Bone Disease, or 'Lobstein syndrome' is disorder of congenital bone fragility caused by mutations in the genes that codify for type I procollagen. This deficiency arises from an amino acid substitution of glycine to bulkier amino acids in the collagen triple helix structure. If the body does not destroy the improper collagen, the relationship between the collagen fibrils and hydroxyapatite crystals to form bone is altered causing brittleness. The following 4 types of osteogenesis imperfecta have been reported. Type I -mild form, type II -extremely severe, type III -severe, type IV -undefined. These partly depend on the genetic subtype. Type I and IV are the most common forms of osteogenesis imperfecta.