OI has high genetic heterogeneity, that is, many different genetic mutations lead to the same or similar sets of observable symptoms (phenotypes).The main causes for developing the disorder are a result of mutations in the COL1A1 and/or COL1A2 genes which are jointly responsible for the production of collagen type I. Approximately 90% of people with OI are heterozygous for mutations in either the COL1A1 or COL1A2 genes. There are several biological factors that are results of the dominant form of OI. These factors include: intracellular stress; abnormal tissue mineralization; abnormal cell to cell interactions; abnormal cell-matrix interactions; a compromised cell matrix structure; and, abnormal interaction between non-collagenous proteins and collagen.Previous research lead to the belief that OI was an autosomal dominant disorder with few other variations in genomes. However, with the lowering of the cost of DNA sequencing in the wake of 2003s Human Genome Project, autosomal recessive forms of the disorder have been identified. Recessive forms of OI relate heavily to defects in the collagen chaperones responsible for production of procollagen and the assembly of the related proteins. Examples of collagen chaperones that are defective in patients with recessive forms of OI include chaperone HSP47 (Cole-Carpenter syndrome) and FKBP65. Mutations in these chaperones result in an improper folding pattern in the collagen 1 proteins which causes the recessive form of the disorder. There are three significant types of OI that are a result of mutations in the collagen prolyl 3-hydroxylation complex (components CRTAP, P3H1, and CyPB).
Protrusio acetabuli is an uncommon defect of the acetabulum, the socket that receives the femoral head to make the hip joint. The hip bone of the pelvic bone/girdle is composed of three bones, the ilium, the ischium and the pubis. In protrusio deformity, there is medial displacement of the femoral head in that the medial aspect of the femoral cortex is medial to the ilioischial line. The socket is too deep and may protrude into the pelvis. Signs and symptoms
Protrusio acetabuli may be asymptomatic. Limitation of joint range of movement is the earliest sign, along with pain. Classification
Protrusio acetabuli is divided into two types, primary and secondary. Primary protrusio acetabuli are characterized by progressive protrusio in middle aged women, and may be associated with osteoarthritis. They may be familial. Secondary protrusio acetabulis causes include femoral head prosthesis, cup arthroplasty, septic arthritis, central fracture dislocation, or total hip replacement surgeryProtrusio acetabuli may also be thought of as unilateral or bilateral. Unilateral protrusio acetabuli may be caused by tuberculous arthritis, trauma, or fibrous dysplasia. Bilateral protrusio acetabuli may be caused by rheumatoid arthritis, Pagets disease, osteomalacia, Marfan syndrome, and ankylosing spondylitis. Prognosis
The protrusio may progress until the femoral neck impinges against the pelvis. Treatment
Arthroscopic surgery (or open joint surgery) is an effective treatment. Joint replacement surgery may be necessary in the case of severe pain or substantial joint restriction. References
External links

McBride MT, Muldoon MP, Santore RF, Trousdale RT, Wenger DR (2001). "Protrusio acetabuli: diagnosis and treatment". J Am Acad Orthop Surg. 9 (2): 79–88. doi:10.5435/00124635-200103000-00002. PMID 11281632.