I am analyzing some cancer samples wherein I have mutations have been detected from normal blood sample and tumor tissue sample of the same patient. Now I am getting mutation that are present in normal but not in tumor sample. What kind of mutation is this?? As far as i know germline mutation should be present in both normal as well as tumor sample as it is from birth and somatic is the one that is present only in tumor sample. How can we have unique mutations in normal sample. Ideally there should not be any unique mutations in normal sample. Am i thinking wrong??