For People With a Family History of MCAD Deficiency By Mayo Clinic Staff For People With a Family History of MCAD Deficiency What will more testing tell me? If you have a family history of MCAD deficiency, it's important to find out which genetic variants run in your family. If the variants in your family are not included in this test, then we cannot determine whether you have them. This means that there is still a possibility that you are a carrier. Talk with your health care provider if you are interested in more-comprehensive testing. If the variants in your family are included in this test, then you are not a carrier of MCAD deficiency. Home For People With a Family History of MCAD Deficiency