Pseudoachondroplasia is caused by a change to the COMP gene (cartilage oligomeric matrix protein). This gene provides instructions for making a protein that is essential for the normal development of cartilage and for its conversion to bone. The COMP protein is normally found in the spaces between cartilage-forming cells (chondrocytes), where it interacts with other proteins. The COMP gene change results in the production of an abnormal COMP protein that cannot be transported out of the cell. The abnormal protein builds up inside the chondrocyte and ultimately leads to early cell death. Early death of the chondrocytes prevents normal bone growth and causes the short stature seen in pseudoachondroplasia. It is estimated to occur in approximately 1 in every 30,000 births.

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