People with a 9q22. 3 microdeletion are missing a sequence of at least 352,000 DNA building blocks (base pairs), also written as 352 kilobases (kb), in the q22. 3 region of chromosome 9. This 352-kb segment is known as the minimum critical region because it is the smallest deletion that has been found to cause the signs and symptoms described above. 9q22. 3 microdeletions can also be much larger; the largest reported deletion includes 20. 5 million base pairs (20. 5 Mb). 9q22. 3 microdeletion affects one of the two copies of chromosome 9 in each cell. People with a 9q22. 3 microdeletion are missing from two to more than 270 genes on chromosome 9. All known 9q22. 3 microdeletions include the PTCH1 gene. The protein produced from this gene, patched-1, acts as a tumor suppressor, which means it keeps cells from growing and dividing (proliferating) too rapidly or in an uncontrolled way. Researchers believe that many of the features associated with 9q22. 3 microdeletions, particularly the signs and symptoms of Gorlin syndrome, result from a loss of the PTCH1 gene. When this gene is missing, patched-1 is not available to suppress cell proliferation. As a result, cells divide uncontrollably to form the tumors that are characteristic of Gorlin syndrome. Other signs and symptoms related to 9q22. 3 microdeletions probably result from the loss of additional genes in the q22. 3 region. Researchers are working to determine which missing genes contribute to the other features associated with the deletion. 
What are the genetic changes related to 9q22.3 microdeletion ?