This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bony dysplasia and soft tissue affection, Subject name: Orthopaedics
Prenatal determination of osteogenesis imperfecta is done by - 
Select and explain. 
A. Acid phosphatase, B. Alkaline phosphatase, C. Abnormal Pro- alpha chain, D. Neutral phosphatase
C: Abnormal Pro- alpha chain
Answer: C: Abnormal Pro- alpha chain 
Explanation: Osteogenesis imperfecta is the most common disorder caused by mutations in this gene. Mutations that inactivate one of the two copies of the COL1A1 gene cause osteogenesis imperfecta type I. The mutated copy of the gene does not produce any pro-alpha1(I) collagen chains. Because only one copy of the gene is directing the cell to make pro-alpha1(I) chains, cells from people with this disorder make only half of the normal amount of type I collagen, which results in bone fragility and other symptoms. ref : maheswari 9th ed