Osteogenesis Imperfecta

Bone is a rigid organ which resembles reinforced concrete. Its principle function is to resist mechanical forces and fractures. Collagen matrix and hydroxyapatite are critical in providing strength and elasticity along with other minerals such as calcium and phosphorus. Clinical disorders associated with bone fragility and bone collagen abnormalities lead to osteogenesis imperfecta. Osteogenesis imperfecta (OI) is a heterogeneous group of genetic disorders characterized primarily by liability to fractures throughout life. The disease is classified on the bases of its phenotypic characteristics ranging from very mild to severe and potentially lethal types. The most prevalent forms of OI is the autosomal dominant types where the disease is caused

When iliac bone specimens of 70 children with OI were studied, it was reported that in OI bone thickness is reduced because of delayed periosteal bone formation. The activity of bone resorption is increased in patients suffering from OI (Rauch and Glorieux, 2004).

The most common clinical manifestations are short stature, hearing loss, neurological complications, blue sclera and brittle teeth. These are caused due to strong defects in collagen fibres. Collagen matrix abnormalities also affect bone mineral phase and leads to increased bone fragility and deformity. Collagen production is examined in skin fibroblasts in most studies. However, there is not enough information about the precise incidence of OI (Martin and Shapiro, 2007)

In recent years, defects in genes encoding the parts of the P3H1-CRTAP-CynB complex (collagen prolyl 3-hydroxylation complex), causes few recessive forms of OI (Sergei and Elena, 2013). Also, mutations in SERPIN H1 which encodes collagen chaperon HSP47; FKBP10 and PLOD2 which encodes foldase and lysyl hydroxylase 2 respectively, needed for forming mature cross-links in bone collagen have been identified.

P3H1-CRTAP-PPIB

It shares a tetratricopeptide-like domain located at their amino terminal portions (Morello et al, 2006). CRTAP deficient infant have characteristic manifestations at birth like growth deficiency and broad undertululated long bones (Morello et al, 2006; Baldridge et al, 2010). The Crtap null mice have chondro-osseous dysplasia with rhizomelia, osteopenia and kyphosis (Morello et al, 2006). About 20 distinct CRTAP mutations are known till date (http://www.le.ac.uk/ge/collagen/). These Probands are thought to be completely inactivating CRTAP which cause severe or lethal OI (Sillence II and III). The CRTAP missense mutation in Proband 3 reveals that disruption of the amino acid sequence of CRTAP leads to OI (Baldridge et al,